534893 research-article2014
JAHXXX10.1177/0898264314534893Journal of Aging and HealthBrown et al.
Article
Veteran Status and Men’s Later-Life Cognitive Trajectories: Evidence from the Health and Retirement Study
Journal of Aging and Health 2014, Vol. 26(6) 924–951 © The Author(s) 2014 Reprints and permissions: sagepub.com/journalsPermissions.nav DOI: 10.1177/0898264314534893 jah.sagepub.com
Maria T. Brown, PhD1, Janet M. Wilmoth, PhD1,2, and Andrew S. London, PhD1,2
Abstract Objective: The aim of this study is to determine the extent to which men’s later-life cognitive trajectories vary by veteran status. Method: We use Health and Retirement Study (HRS) data to estimate growth curve models examining men’s later-life cognitive trajectories by veteran status, war service status, and period of service. Analyses control for early-life characteristics that influence selection into military service and later-life cognition, and midto late-life characteristics that potentially mediate the relationship between military service and later-life cognition. Results: Veterans have higher cognition scores relative to nonveterans around retirement age, but their cognition scores decline more rapidly with increasing age, such that cognition scores are similar in both groups among the oldest old. Veterans who served during the Korean War have lower cognition scores around retirement age, but less steep age-related declines, than veterans who served during World War II. Discussion: Findings are discussed in relation to the extant literature, future research, potential service needs, and study limitations.
1Aging
Studies Institute, Syracuse University, NY, USA of Sociology, Syracuse University, NY, USA
2Department
Corresponding Author: Maria T. Brown, Aging Studies Institute, Syracuse University, 320D Lyman Hall, Syracuse, NY 13244, USA. Email: [email protected]
Brown et al.
925
Keywords cognitive trajectories, veterans, life course
Many older adults experience some degree of cognitive decline with age. Usually, cognitive decline manifests as mild cognitive impairment, which is cognitive functioning within the normal range, but the individual complains about memory problems (Bennett et al., 2002; Larrieu et al., 2002). More severe, mid- and later-life cognitive decline often results from disease processes that interfere with normal brain functioning (Alzheimer’s Association, 2012). The extant literature is replete with studies that identify life-course factors that influence normal and disease-related changes in cognitive functioning among older adults (Borenstein, Copenhaver, & Mortimer, 2006; Douthit & Dannefer, 2006; Glymour & Manly, 2008). However, to date, no studies have considered the influence of military service on later-life cognitive trajectories even though a large percentage of men from early- and mid-20th-century birth cohorts served in the military (Wilmoth & London, 2011). The impetus to address this gap in the literature derives from evidence that male veterans have lower odds of memory-related disability than male nonveterans (Wilmoth, London, & Parker, 2011) and that health changes among older men, which may be associated with later-life cognitive change, differ by veteran status and by military service experience (Wilmoth, London, & Parker, 2010). In this article, we draw on the life-course perspective and prior research on the life-course consequences of military service (Wilmoth & London, 2013) to argue that prior military service—as indicated by veteran, war service, and period of service statuses—has enduring effects that have the potential to influence later-life cognitive functioning. We begin by briefly reviewing the extant literature on life-course factors that influence later-life cognition and outlining a theoretical rationale for including veteran status in empirical models of later-life cognitive change. We then use data from the 1995-2006 waves of the Health and Retirement Study (HRS) to estimate growth curve models that examine differences in men’s cognition trajectories by veteran status. We focus on men because there are so few older women from earlyand mid-20th-century birth cohorts who experienced military service. Specifically, building on prior research (Wilmoth et al., 2010), we address the following research questions: Research Question 1: Do men’s trajectories of later-life cognitive change vary by veteran status (among all men), by war service status (among veterans), and by period of service (among war service veterans)?
926
Journal of Aging and Health 26(6)
Research Question 2: Does controlling for early-life characteristics, which shape selection into military service, and potentially mediating mid- to late-life characteristics, attenuate the relationship between men’s later-life cognitive change and veteran, war service, and period of war service statuses, respectively?
Life-Course Influences on Later-Life Cognition Previous research indicates that numerous early- to mid-life characteristics associated with military service also shape later-life cognition. For example, ascribed characteristics, such as sex and race/ethnicity, are important sources of variation in later-life cognition. Findings regarding the associations between sex and cognitive decline or dementia are mixed (Edland, Rocca, Petersen, Cha, & Kokmen, 2002; Lindsay et al., 2002), with some studies finding women to be at greater risk for dementia and other studies finding no significant difference between men and women. By contrast, racial/ethnic differences in cognitive functioning in later life are well-established (Sloan & Wang, 2005), with most studies finding that minority elders perform less well than Whites on cognition scales. Usually, controlling statistically for education and other potentially mediating socioenvironmental factors substantially reduces observed associations (Mehta et al., 2004). Previous research has also documented relationships between socioeconomic status (SES) and cognitive functioning in childhood, adulthood, and old age (Everson-Rose, Mendes de Leon, Bienias, Wilson, & Evans, 2003; Kaplan et al., 2001). Few studies examine the relationship between early-life SES—which is usually measured by parental educational attainment, occupational prestige, and family SES, or a composite index of these characteristics—and cognitive decline in old age (Borenstein et al., 2006; Brown, 2010; Everson-Rose et al., 2003; Luo & Waite, 2005). However, childhood socioeconomic disadvantage has been linked to adult health status and behaviors, major depression, and physical functioning in later life (Guralnik, Butterworth, Wadsworth, & Kuh, 2006; Turrell, Lynch, Leite, Raghunathan, & Kaplan, 2007), which are factors that are associated with later-life cognitive functioning. Thus, childhood socioeconomic disadvantage may affect cognitive functioning in later life by influencing early-childhood cognitive development, as well as by shaping midlife cognition-related demographic, economic, health, and well-being outcomes that influence trajectories of cognitive development and decline across the adult life course. A variety of factors in mid- and later life have been linked to cognitive functioning in older adults, including education (Lindsay et al., 2002), income, marital status, and some health behaviors (Herzog & Wallace, 1997).
Brown et al.
927
Impaired cognitive function is associated with various diseases or conditions in older adults, including cardiovascular disease, stroke, hypertension, and diabetes (Blaum, Ofstedal, & Liang, 2002; Haan et al., 2003; Taylor, 2008). In light of evidence documenting relationships between socioeconomic disadvantage, health problems, and cognitive functioning, some researchers have conceptualized decreased cognitive functioning in later life as a “marker of lifelong adversity” (Moody-Ayers, Mehta, Lindquist, Sands, & Covinsky, 2005, p. 933).
Military Service and Later-Life Cognition Although there is an extensive literature on the life-course consequences of military service that compares veterans to nonveterans (Wilmoth & London, 2013), few studies have examined whether cognition varies by veteran status. This is unfortunate given that many of the early-life factors that the literature identifies as being associated with later-life cognition are also associated with veteran status. For example, various disabilities and health problems prevent military service in all eras, although the particular disqualifying conditions and preinduction physical exam rejection rates have changed over time (Wolf, Wing, & Lopoo, 2013). Among early- to mid-20th century birth cohorts, men (Campbell, 2013; Kelty & Segal, 2013), Whites (Lutz, 2008, 2013), and those from socioeconomically disadvantaged backgrounds (Bennett & McDonald, 2013) disproportionately served in the military. However, the midcentury racial integration of the military, policy changes related to women’s participation, the draft, and the subsequent shift to the All-Volunteer Force have changed service-related opportunities for racial/ ethnic minorities, women, and individuals from various social classes. Other factors are potentially affected by military service, such as educational attainment (Bennett & McDonald, 2013), employment (Kleykamp, 2013), income (Bennett & McDonald, 2013; Kelty & Segal, 2013), marriage and family outcomes (Burland & Lundquist, 2013; London, Allen, & Wilmoth, 2013; Usdansky, London, & Wilmoth, 2009), and health and disability (MacLean, 2013; Wilmoth et al., 2010, 2011). Although the effects of military service on these cognition-related mid- and later-life outcomes is variable across historical periods, policy contexts, and individual characteristics (Wilmoth & London, 2013), these factors have the potential to mediate the relationship between military service, which tends to begin and end relatively early in the life course, and later-life cognitive functioning. Adopting a life-course perspective draws attention to the need for researchers to consider selection into military service in studies of the “effects” of military service, control for selection to the extent possible with available data and
928
Journal of Aging and Health 26(6)
methods, and interpret results cautiously (Wolf et al., 2013). A life-course perspective also facilitates the examination of both the effect of prior military service on later-life cognition, net of early-life controls, and the possible pathways by which military service influences cognitive change in later life. Although there is a substantial literature that examines cognition among veterans (Roca, Hart, Kimbrell, & Freeman, 2006; Wray et al., 2012; Yehuda, Golier, Tischler, Stavitsky, & Harvey, 2005), no studies examine veteran status differences and change in later-life cognitive outcomes. One recent study based on data from the 2000 U.S. Census of Population documents that veteran status is significantly associated with self-reported memory-related disability, although the direction of the association differs for women and men (Wilmoth et al., 2011). Overall, 7.56% of female veterans and 6.13% of male veterans reported memory-related disability, compared with 5.69% of female nonveterans and 4.78% of male nonveterans, respectively. In sex-specific multivariate logistic regression models that controlled for age, race/ethnicity, marital status, education, citizenship, and region, the odds of having a memory disability were significantly higher among female veterans than among female nonveterans (adjusted odds ratio [AOR] = 1.18, p < .001) and significantly lower among male veterans than among male nonveterans (AOR = 0.93, p < .001). Although this study did not report results by age, these findings demonstrate that veteran status is associated with memory-related disability and raise questions about how and why veteran status affects cognition in later life. There are various theoretical reasons to expect that later-life cognition might differ by veteran status. On the one hand, veterans may have better cognitive functioning in later life than nonveterans because the military has relatively stringent physical, mental, and moral standards for admission and rejects potential recruits who are overweight, in poor health, or have apparent moral shortcomings (Sackett & Mavor, 2006). To the extent that the factors that select people into the military are associated beneficially with cognitive development or subsequent cognitive decline across the life course, such selectivity has the potential to contribute to the appearance of a positive association between veteran status and better later-life cognition. Beyond selection, military service may generally contribute to better cognitive outcomes by increasing access to training and education through the GI Bill, health care, and a range of other resources that improve living conditions (Wilmoth & London, 2011). It may also contribute to better employment, earnings, and wealth outcomes (Kleykamp, 2013; Street & Hoffman, 2013), although recent evidence indicates that, among the working-aged, the veteran advantage with respect to poverty and material hardship is substantially eroded when the veteran is disabled (Heflin, Wilmoth, & London, 2012; London,
Brown et al.
929
Heflin, & Wilmoth, 2011). Veterans may also see some long-term benefits from the physical training and fitness required during the period of active-duty service, or from exercise and lifestyle patterns that carry over from the activeduty period into later life in ways that are beneficial for health and well-being, and, ultimately, cognition. In addition, entering the military may “knife off” negative influences from earlier in life and provide a “bridging environment” to better health care resources, education, and training opportunities through the Department of Veterans Affairs (Bound & Turner, 2002; Elder, 1986, 1987; MacLean, 2005; Sampson & Laub, 1996). Although access to these resources varies by race/ethnicity and historical context (Mettler, 2005; Teachman & Call, 1996), it is plausible that military service may be associated with better cognition in later life by setting veterans, particularly those from disadvantaged backgrounds and unharmed by their service, on better trajectories through life than similar nonveterans. On the other hand, veterans may have worse later-life cognitive functioning than nonveterans because they are selected disproportionately from disadvantaged backgrounds (Bennett & McDonald, 2013). Early-life disadvantage may have lifelong consequences for cognition outcomes despite stringent preservice screening and the potential for military service to function as a positive turning point in the life course. More direct, negative influences of military service on cognition may result from service-connected injuries or exposure to hazardous environments that impair health and wellbeing, and, ultimately, cognitive functioning. The military has historically exposed service members to risky health behaviors, either by subsidizing tobacco products or by placing service members in environments conducive to heavy alcohol and substance use (Bedard & Deschênes, 2006; Clipp & Elder, 1996; Elder & Clipp, 1988, 1989; Elder, Clipp, Brown, Martin, & Friedman, 2009; Miech, London, Wilmoth, & Koester, 2013). Combat exposure is also linked to greater risk of short-term injuries and long-term physical disability (Elder, Shanahan, & Clipp, 1997), and physical and mental health problems (Elder et al., 2009; Vogt, King, King, Savarese, & Suvak, 2004). Relatively early-life traumatic brain injuries or service-connected sensory impairments may negatively affect cognition in later life. Much of the literature on cognitive function in veterans is linked to the psychological effects of combat, such as posttraumatic stress disorder (PTSD), with or without the presence of other psychological disorders (Roca et al., 2006; Yaffe et al., 2010; Yehuda et al., 2005). Golier and colleagues (2002) hypothesized that PTSD affects memory in older adults by accelerating memory decline. Their research on Holocaust survivors linked severe and prolonged trauma, and resulting long-term PTSD, to greater cognitive burden later in the life course (Golier et al., 2002). Similar cognitive deficits were
930
Journal of Aging and Health 26(6)
found in older combat veterans with PTSD (Yehuda et al., 2005), although their cognitive deficits manifested differently. The negative effects of combat exposure are seen among veterans of all wars (Frey-Wouters & Laufer, 1986; Kulka et al., 1990; Teachman & Call, 1996); however, as is the case with other health outcomes (Wilmoth et al., 2010), veterans who served during different historical periods and wars may have different cognitive trajectories. Veterans, in general, and war veterans, in particular, might also suffer worse cognitive functioning in later life due to associated declines in physical health. A recent longitudinal study documents that older male veterans had better health than nonveterans around retirement age, but experienced greater age-related changes in health than nonveterans net of a range of early-life and time-varying later-life controls (Wilmoth et al., 2010). Similarly, men who served during wartime had better health at the mean age, but more-rapid agerelated changes in health than men who did not serve during wartime. Among war veterans, Vietnam War veterans were in poorer health at the mean age, but they experienced less substantial age-related health changes than men who served during previous wars. World War II (WWII) and Korean War veterans experienced particularly steep age-related increases in activities of daily living (ADL) limitations and decreases in self-rated health compared with Vietnam War veterans. The known connections between cognitive function and a variety of chronic conditions in older adults, and the documented differences in health change between older veterans and nonveterans, as well as veterans with differing military service experiences, point to the need for research that examines whether there are veteran status disparities in later-life cognitive functioning. Based on current knowledge regarding the effects of military service across the life course, we expect later-life cognitive functioning to be poorer, and declines in cognitive functioning to be steeper, among veterans (compared with nonveterans), war service veterans (compared with nonwar service veterans), and veterans who potentially had longer durations of service because they served during multiple wars (compared with veterans who served only during WWII or the Korean War).
Method Sample This study uses data from the 1995 to 2006 longitudinal Assets and Health Dynamics Among the Oldest Old (AHEAD), HRS, and RAND HRS files (henceforth HRS). The analytic sample for this study includes 6,863 men born between 1895 and 1941. During the 11 years of the study, these men
Brown et al.
931
contributed 21,438 observations to the person–period file that we use to estimate growth curve models. The person–period file only contains observations for HRS age-eligible respondents who were old enough to participate in the cognition portion of the interview (i.e., age 65 years or older) and able to complete the self-interview without the assistance of a proxy. Because so few Vietnam War veterans were old enough to participate in the cognition portion of the interview (i.e., less than 2% served only during the Vietnam War), we deleted all Vietnam War veterans from the analytic sample. As noted previously, the analysis does not include women because less than 1% (135) of the 14,491 women in the HRS served in the military.
Measures Dependent Variables The HRS measured cognitive functioning using a modified version of the Telephone Interview for Cognitive Status (TICS) instrument. In the late 1980s, the developers of the TICS drew on then-current state-of-the-science understandings of the dimensions of cognition (Zsembik & Peek, 2001) and designed it to collect a comprehensive range of information on cognitive functioning. The TICS is a validated measure of cognitive functioning (Zsembik & Peek, 2001) that is based on Folstein’s Mini Mental Status Exam (MMSE). The MMSE is a commonly used instrument for assessing dementia in clinical settings that can be reliably administered by telephone (Freedman, Aykan, & Martin, 2001; Herzog & Wallace, 1997). For the HRS, the TICS was modified to measure six tasks, with a maximum score of 35 points. These tasks evaluate memory and executive function as aspects of cognitive function, and weight fluid cognitive measures more heavily than in the original instrument (Freedman et al., 2001; Herzog & Wallace, 1997).
Military Service Variables The retrospective report of service in the military identifies men who have experienced “active military service,” not including service in the military reserves. Respondents who report military service answer follow-up questions about start and stop dates. We assumed that service was continuous and used these dates to determine service during WWII (1941-1946) and the Korean War (1950-1955). We used start and stop dates for the wars that are the same as those used by the Veterans Administration to determine eligibility for wartime service benefits. They include periods of combat as well as occupation. We then constructed three military service measures: veteran status
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(yes = 1), wartime service (yes = 1), and period of service (only WWII, only Korea, and both WWI and Korea). We use the veteran status and wartime service variables to identify the appropriate subpopulations of veterans and wartime veterans for specific analyses.
Control Variables The analysis includes a broad range of control variables, which prior research indicates are associated with both veteran status and later-life cognition. The first set of control variables are retrospectively reported early-life characteristics that occurred prior to military service: race/ethnicity, early-life socioeconomic disadvantage, and early-life health. Race/ethnicity includes non-Hispanic White (reference), non-Hispanic Black, non-Hispanic other race, and Hispanic (of any race). Early-life disadvantage is an indexed scale, which is comprised of four dichotomously coded variables: mother’s education and father’s education (
JAHXXX10.1177/0898264314534893Journal of Aging and HealthBrown et al.
Article
Veteran Status and Men’s Later-Life Cognitive Trajectories: Evidence from the Health and Retirement Study
Journal of Aging and Health 2014, Vol. 26(6) 924–951 © The Author(s) 2014 Reprints and permissions: sagepub.com/journalsPermissions.nav DOI: 10.1177/0898264314534893 jah.sagepub.com
Maria T. Brown, PhD1, Janet M. Wilmoth, PhD1,2, and Andrew S. London, PhD1,2
Abstract Objective: The aim of this study is to determine the extent to which men’s later-life cognitive trajectories vary by veteran status. Method: We use Health and Retirement Study (HRS) data to estimate growth curve models examining men’s later-life cognitive trajectories by veteran status, war service status, and period of service. Analyses control for early-life characteristics that influence selection into military service and later-life cognition, and midto late-life characteristics that potentially mediate the relationship between military service and later-life cognition. Results: Veterans have higher cognition scores relative to nonveterans around retirement age, but their cognition scores decline more rapidly with increasing age, such that cognition scores are similar in both groups among the oldest old. Veterans who served during the Korean War have lower cognition scores around retirement age, but less steep age-related declines, than veterans who served during World War II. Discussion: Findings are discussed in relation to the extant literature, future research, potential service needs, and study limitations.
1Aging
Studies Institute, Syracuse University, NY, USA of Sociology, Syracuse University, NY, USA
2Department
Corresponding Author: Maria T. Brown, Aging Studies Institute, Syracuse University, 320D Lyman Hall, Syracuse, NY 13244, USA. Email: [email protected]
Brown et al.
925
Keywords cognitive trajectories, veterans, life course
Many older adults experience some degree of cognitive decline with age. Usually, cognitive decline manifests as mild cognitive impairment, which is cognitive functioning within the normal range, but the individual complains about memory problems (Bennett et al., 2002; Larrieu et al., 2002). More severe, mid- and later-life cognitive decline often results from disease processes that interfere with normal brain functioning (Alzheimer’s Association, 2012). The extant literature is replete with studies that identify life-course factors that influence normal and disease-related changes in cognitive functioning among older adults (Borenstein, Copenhaver, & Mortimer, 2006; Douthit & Dannefer, 2006; Glymour & Manly, 2008). However, to date, no studies have considered the influence of military service on later-life cognitive trajectories even though a large percentage of men from early- and mid-20th-century birth cohorts served in the military (Wilmoth & London, 2011). The impetus to address this gap in the literature derives from evidence that male veterans have lower odds of memory-related disability than male nonveterans (Wilmoth, London, & Parker, 2011) and that health changes among older men, which may be associated with later-life cognitive change, differ by veteran status and by military service experience (Wilmoth, London, & Parker, 2010). In this article, we draw on the life-course perspective and prior research on the life-course consequences of military service (Wilmoth & London, 2013) to argue that prior military service—as indicated by veteran, war service, and period of service statuses—has enduring effects that have the potential to influence later-life cognitive functioning. We begin by briefly reviewing the extant literature on life-course factors that influence later-life cognition and outlining a theoretical rationale for including veteran status in empirical models of later-life cognitive change. We then use data from the 1995-2006 waves of the Health and Retirement Study (HRS) to estimate growth curve models that examine differences in men’s cognition trajectories by veteran status. We focus on men because there are so few older women from earlyand mid-20th-century birth cohorts who experienced military service. Specifically, building on prior research (Wilmoth et al., 2010), we address the following research questions: Research Question 1: Do men’s trajectories of later-life cognitive change vary by veteran status (among all men), by war service status (among veterans), and by period of service (among war service veterans)?
926
Journal of Aging and Health 26(6)
Research Question 2: Does controlling for early-life characteristics, which shape selection into military service, and potentially mediating mid- to late-life characteristics, attenuate the relationship between men’s later-life cognitive change and veteran, war service, and period of war service statuses, respectively?
Life-Course Influences on Later-Life Cognition Previous research indicates that numerous early- to mid-life characteristics associated with military service also shape later-life cognition. For example, ascribed characteristics, such as sex and race/ethnicity, are important sources of variation in later-life cognition. Findings regarding the associations between sex and cognitive decline or dementia are mixed (Edland, Rocca, Petersen, Cha, & Kokmen, 2002; Lindsay et al., 2002), with some studies finding women to be at greater risk for dementia and other studies finding no significant difference between men and women. By contrast, racial/ethnic differences in cognitive functioning in later life are well-established (Sloan & Wang, 2005), with most studies finding that minority elders perform less well than Whites on cognition scales. Usually, controlling statistically for education and other potentially mediating socioenvironmental factors substantially reduces observed associations (Mehta et al., 2004). Previous research has also documented relationships between socioeconomic status (SES) and cognitive functioning in childhood, adulthood, and old age (Everson-Rose, Mendes de Leon, Bienias, Wilson, & Evans, 2003; Kaplan et al., 2001). Few studies examine the relationship between early-life SES—which is usually measured by parental educational attainment, occupational prestige, and family SES, or a composite index of these characteristics—and cognitive decline in old age (Borenstein et al., 2006; Brown, 2010; Everson-Rose et al., 2003; Luo & Waite, 2005). However, childhood socioeconomic disadvantage has been linked to adult health status and behaviors, major depression, and physical functioning in later life (Guralnik, Butterworth, Wadsworth, & Kuh, 2006; Turrell, Lynch, Leite, Raghunathan, & Kaplan, 2007), which are factors that are associated with later-life cognitive functioning. Thus, childhood socioeconomic disadvantage may affect cognitive functioning in later life by influencing early-childhood cognitive development, as well as by shaping midlife cognition-related demographic, economic, health, and well-being outcomes that influence trajectories of cognitive development and decline across the adult life course. A variety of factors in mid- and later life have been linked to cognitive functioning in older adults, including education (Lindsay et al., 2002), income, marital status, and some health behaviors (Herzog & Wallace, 1997).
Brown et al.
927
Impaired cognitive function is associated with various diseases or conditions in older adults, including cardiovascular disease, stroke, hypertension, and diabetes (Blaum, Ofstedal, & Liang, 2002; Haan et al., 2003; Taylor, 2008). In light of evidence documenting relationships between socioeconomic disadvantage, health problems, and cognitive functioning, some researchers have conceptualized decreased cognitive functioning in later life as a “marker of lifelong adversity” (Moody-Ayers, Mehta, Lindquist, Sands, & Covinsky, 2005, p. 933).
Military Service and Later-Life Cognition Although there is an extensive literature on the life-course consequences of military service that compares veterans to nonveterans (Wilmoth & London, 2013), few studies have examined whether cognition varies by veteran status. This is unfortunate given that many of the early-life factors that the literature identifies as being associated with later-life cognition are also associated with veteran status. For example, various disabilities and health problems prevent military service in all eras, although the particular disqualifying conditions and preinduction physical exam rejection rates have changed over time (Wolf, Wing, & Lopoo, 2013). Among early- to mid-20th century birth cohorts, men (Campbell, 2013; Kelty & Segal, 2013), Whites (Lutz, 2008, 2013), and those from socioeconomically disadvantaged backgrounds (Bennett & McDonald, 2013) disproportionately served in the military. However, the midcentury racial integration of the military, policy changes related to women’s participation, the draft, and the subsequent shift to the All-Volunteer Force have changed service-related opportunities for racial/ ethnic minorities, women, and individuals from various social classes. Other factors are potentially affected by military service, such as educational attainment (Bennett & McDonald, 2013), employment (Kleykamp, 2013), income (Bennett & McDonald, 2013; Kelty & Segal, 2013), marriage and family outcomes (Burland & Lundquist, 2013; London, Allen, & Wilmoth, 2013; Usdansky, London, & Wilmoth, 2009), and health and disability (MacLean, 2013; Wilmoth et al., 2010, 2011). Although the effects of military service on these cognition-related mid- and later-life outcomes is variable across historical periods, policy contexts, and individual characteristics (Wilmoth & London, 2013), these factors have the potential to mediate the relationship between military service, which tends to begin and end relatively early in the life course, and later-life cognitive functioning. Adopting a life-course perspective draws attention to the need for researchers to consider selection into military service in studies of the “effects” of military service, control for selection to the extent possible with available data and
928
Journal of Aging and Health 26(6)
methods, and interpret results cautiously (Wolf et al., 2013). A life-course perspective also facilitates the examination of both the effect of prior military service on later-life cognition, net of early-life controls, and the possible pathways by which military service influences cognitive change in later life. Although there is a substantial literature that examines cognition among veterans (Roca, Hart, Kimbrell, & Freeman, 2006; Wray et al., 2012; Yehuda, Golier, Tischler, Stavitsky, & Harvey, 2005), no studies examine veteran status differences and change in later-life cognitive outcomes. One recent study based on data from the 2000 U.S. Census of Population documents that veteran status is significantly associated with self-reported memory-related disability, although the direction of the association differs for women and men (Wilmoth et al., 2011). Overall, 7.56% of female veterans and 6.13% of male veterans reported memory-related disability, compared with 5.69% of female nonveterans and 4.78% of male nonveterans, respectively. In sex-specific multivariate logistic regression models that controlled for age, race/ethnicity, marital status, education, citizenship, and region, the odds of having a memory disability were significantly higher among female veterans than among female nonveterans (adjusted odds ratio [AOR] = 1.18, p < .001) and significantly lower among male veterans than among male nonveterans (AOR = 0.93, p < .001). Although this study did not report results by age, these findings demonstrate that veteran status is associated with memory-related disability and raise questions about how and why veteran status affects cognition in later life. There are various theoretical reasons to expect that later-life cognition might differ by veteran status. On the one hand, veterans may have better cognitive functioning in later life than nonveterans because the military has relatively stringent physical, mental, and moral standards for admission and rejects potential recruits who are overweight, in poor health, or have apparent moral shortcomings (Sackett & Mavor, 2006). To the extent that the factors that select people into the military are associated beneficially with cognitive development or subsequent cognitive decline across the life course, such selectivity has the potential to contribute to the appearance of a positive association between veteran status and better later-life cognition. Beyond selection, military service may generally contribute to better cognitive outcomes by increasing access to training and education through the GI Bill, health care, and a range of other resources that improve living conditions (Wilmoth & London, 2011). It may also contribute to better employment, earnings, and wealth outcomes (Kleykamp, 2013; Street & Hoffman, 2013), although recent evidence indicates that, among the working-aged, the veteran advantage with respect to poverty and material hardship is substantially eroded when the veteran is disabled (Heflin, Wilmoth, & London, 2012; London,
Brown et al.
929
Heflin, & Wilmoth, 2011). Veterans may also see some long-term benefits from the physical training and fitness required during the period of active-duty service, or from exercise and lifestyle patterns that carry over from the activeduty period into later life in ways that are beneficial for health and well-being, and, ultimately, cognition. In addition, entering the military may “knife off” negative influences from earlier in life and provide a “bridging environment” to better health care resources, education, and training opportunities through the Department of Veterans Affairs (Bound & Turner, 2002; Elder, 1986, 1987; MacLean, 2005; Sampson & Laub, 1996). Although access to these resources varies by race/ethnicity and historical context (Mettler, 2005; Teachman & Call, 1996), it is plausible that military service may be associated with better cognition in later life by setting veterans, particularly those from disadvantaged backgrounds and unharmed by their service, on better trajectories through life than similar nonveterans. On the other hand, veterans may have worse later-life cognitive functioning than nonveterans because they are selected disproportionately from disadvantaged backgrounds (Bennett & McDonald, 2013). Early-life disadvantage may have lifelong consequences for cognition outcomes despite stringent preservice screening and the potential for military service to function as a positive turning point in the life course. More direct, negative influences of military service on cognition may result from service-connected injuries or exposure to hazardous environments that impair health and wellbeing, and, ultimately, cognitive functioning. The military has historically exposed service members to risky health behaviors, either by subsidizing tobacco products or by placing service members in environments conducive to heavy alcohol and substance use (Bedard & Deschênes, 2006; Clipp & Elder, 1996; Elder & Clipp, 1988, 1989; Elder, Clipp, Brown, Martin, & Friedman, 2009; Miech, London, Wilmoth, & Koester, 2013). Combat exposure is also linked to greater risk of short-term injuries and long-term physical disability (Elder, Shanahan, & Clipp, 1997), and physical and mental health problems (Elder et al., 2009; Vogt, King, King, Savarese, & Suvak, 2004). Relatively early-life traumatic brain injuries or service-connected sensory impairments may negatively affect cognition in later life. Much of the literature on cognitive function in veterans is linked to the psychological effects of combat, such as posttraumatic stress disorder (PTSD), with or without the presence of other psychological disorders (Roca et al., 2006; Yaffe et al., 2010; Yehuda et al., 2005). Golier and colleagues (2002) hypothesized that PTSD affects memory in older adults by accelerating memory decline. Their research on Holocaust survivors linked severe and prolonged trauma, and resulting long-term PTSD, to greater cognitive burden later in the life course (Golier et al., 2002). Similar cognitive deficits were
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found in older combat veterans with PTSD (Yehuda et al., 2005), although their cognitive deficits manifested differently. The negative effects of combat exposure are seen among veterans of all wars (Frey-Wouters & Laufer, 1986; Kulka et al., 1990; Teachman & Call, 1996); however, as is the case with other health outcomes (Wilmoth et al., 2010), veterans who served during different historical periods and wars may have different cognitive trajectories. Veterans, in general, and war veterans, in particular, might also suffer worse cognitive functioning in later life due to associated declines in physical health. A recent longitudinal study documents that older male veterans had better health than nonveterans around retirement age, but experienced greater age-related changes in health than nonveterans net of a range of early-life and time-varying later-life controls (Wilmoth et al., 2010). Similarly, men who served during wartime had better health at the mean age, but more-rapid agerelated changes in health than men who did not serve during wartime. Among war veterans, Vietnam War veterans were in poorer health at the mean age, but they experienced less substantial age-related health changes than men who served during previous wars. World War II (WWII) and Korean War veterans experienced particularly steep age-related increases in activities of daily living (ADL) limitations and decreases in self-rated health compared with Vietnam War veterans. The known connections between cognitive function and a variety of chronic conditions in older adults, and the documented differences in health change between older veterans and nonveterans, as well as veterans with differing military service experiences, point to the need for research that examines whether there are veteran status disparities in later-life cognitive functioning. Based on current knowledge regarding the effects of military service across the life course, we expect later-life cognitive functioning to be poorer, and declines in cognitive functioning to be steeper, among veterans (compared with nonveterans), war service veterans (compared with nonwar service veterans), and veterans who potentially had longer durations of service because they served during multiple wars (compared with veterans who served only during WWII or the Korean War).
Method Sample This study uses data from the 1995 to 2006 longitudinal Assets and Health Dynamics Among the Oldest Old (AHEAD), HRS, and RAND HRS files (henceforth HRS). The analytic sample for this study includes 6,863 men born between 1895 and 1941. During the 11 years of the study, these men
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contributed 21,438 observations to the person–period file that we use to estimate growth curve models. The person–period file only contains observations for HRS age-eligible respondents who were old enough to participate in the cognition portion of the interview (i.e., age 65 years or older) and able to complete the self-interview without the assistance of a proxy. Because so few Vietnam War veterans were old enough to participate in the cognition portion of the interview (i.e., less than 2% served only during the Vietnam War), we deleted all Vietnam War veterans from the analytic sample. As noted previously, the analysis does not include women because less than 1% (135) of the 14,491 women in the HRS served in the military.
Measures Dependent Variables The HRS measured cognitive functioning using a modified version of the Telephone Interview for Cognitive Status (TICS) instrument. In the late 1980s, the developers of the TICS drew on then-current state-of-the-science understandings of the dimensions of cognition (Zsembik & Peek, 2001) and designed it to collect a comprehensive range of information on cognitive functioning. The TICS is a validated measure of cognitive functioning (Zsembik & Peek, 2001) that is based on Folstein’s Mini Mental Status Exam (MMSE). The MMSE is a commonly used instrument for assessing dementia in clinical settings that can be reliably administered by telephone (Freedman, Aykan, & Martin, 2001; Herzog & Wallace, 1997). For the HRS, the TICS was modified to measure six tasks, with a maximum score of 35 points. These tasks evaluate memory and executive function as aspects of cognitive function, and weight fluid cognitive measures more heavily than in the original instrument (Freedman et al., 2001; Herzog & Wallace, 1997).
Military Service Variables The retrospective report of service in the military identifies men who have experienced “active military service,” not including service in the military reserves. Respondents who report military service answer follow-up questions about start and stop dates. We assumed that service was continuous and used these dates to determine service during WWII (1941-1946) and the Korean War (1950-1955). We used start and stop dates for the wars that are the same as those used by the Veterans Administration to determine eligibility for wartime service benefits. They include periods of combat as well as occupation. We then constructed three military service measures: veteran status
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(yes = 1), wartime service (yes = 1), and period of service (only WWII, only Korea, and both WWI and Korea). We use the veteran status and wartime service variables to identify the appropriate subpopulations of veterans and wartime veterans for specific analyses.
Control Variables The analysis includes a broad range of control variables, which prior research indicates are associated with both veteran status and later-life cognition. The first set of control variables are retrospectively reported early-life characteristics that occurred prior to military service: race/ethnicity, early-life socioeconomic disadvantage, and early-life health. Race/ethnicity includes non-Hispanic White (reference), non-Hispanic Black, non-Hispanic other race, and Hispanic (of any race). Early-life disadvantage is an indexed scale, which is comprised of four dichotomously coded variables: mother’s education and father’s education (
