Employment Status and Heart Disease Risk Factors in Middle-Aged Women: The Rancho Bernardo Study
...I........I.I.I.I...-.-.-
..Im -1- MEN
Donna Kritz-Silverstein, PhD, Deborah L. Barrett-Connor, MD
Introduction Heart disease is the leading cause of death among both men and women.12 In men, risk of heart disease is related to employment.3'4 However, although more and more women have been entering the labor force in recent years,-7 few studies have examined employment and heart disease risk factors in women, and their findings have been inconsistent.3,48-_1''. Among young women in the Framingham Offspring Study, homemakers and those employed outside the home were compared and showed no significant differences in blood pressure, total cholesterol, high-density lipoprotein (HDL) level, or low-density lipoprotein (LDL) level over an 8-year period. '° In contrast, Hazuda et al.9 found highly significant differences in HDL and in ratio of HDL to total cholesterol, triglycerides, and fasting and postchallenge plasma glucose favoring employed women over homemakers. These differences were not explained by age, socioeconomic status, obesity, exercise, smoking, alcohol consumption, or use of estrogen. We studied the association of employment status and heart disease risk factors in middle-aged White women. We examined differences between employed and nonemployed women in blood pressure, lipid and lipoprotein levels, and fasting and postchallenge plasma glucose and insulin levels before and after adjusting for potentially confounding physical and lifestyle covariates.
Methods The population consisted of women who were initially enrolled in the Rancho Bernardo Heart and Chronic Disease Sur-
Wingard, PhD,
and Elizabeth
vey between 1972 and 1974 and who attended a follow-up clinic visit between 1984 and 1987; 84% of surviving women aged 40 and older responded. This report is based on the 242 women aged 40 through 59 at the follow-up visit who had fasted the requested 12 hours and were not currently taking lipid-lowering medications. This age group was chosen for analysis because there were too few women over age 59 who were still working. Only one woman was excluded for not fasting the requested 12 hours, and three women were excluded because they were using lipid-lowering medications.
Data Collection A standardized interview was used to obtain information on current employment status, marital status, cigarette smoking, alcohol consumption (number of drinks per week of beer, wine, or liquor converted to milliliters of alcohol per week), and exercise (whether subjects exercised three or more times per week). Reported current use of estrogen and other medications was confirmed by prescriptions or pill containers brought to the clinic for that purpose. In the clinic, height (meters), weight (kilograms), and waist and hip circumferences (centimeters) were measured with The authors are with the Department of Community and Family Medicine, Division of Epidemiology, at the University of California, San
Diego. Requests for reprints should be sent to Elizabeth Barrett-Connor, MD, Division of Epidemiology, Department of Community and Family Medicine, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 920930607. This paper was submitted to the journal January 31, 1991, and accepted with revisions
September 16, 1991.
American Journal of Public Health 215
Keiz-Sivertein et al.
Results
the participants in light clothing and without shoes. Body mass index (weight/ height2) and waist-hip ratio (waist circumference/hip circumference x 100) were used to estimate obesity and central
adiposity, respectively. An oral glucose tolerance test with a 75-g glucose load was performed between 7 AM and 11 AM after a 12-hour fast. Blood was obtained by venipuncture before and 2 hours after the glucose challenge. Lipids and lipoproteins were measured in a Lipid Research Clinics laboratory under the continuous standardization program of the Centers for Disease Control in Atlanta, Ga. Fasting plasma total cholesterol and triglyceride levels were measured by enzymatic techniques with an ABA-200 biochromatic analyzer (Abbott Laboratories, Irving, Tex), a highperformance cholesterol reagent (No. 236691, Boehringer-Mannheim Diagnostics, Indianapolis, Ind), and a triglyceride agent (No. 6097, Abbot Laboratories). HDL cholesterol was measured by precipitating the other lipoproteins with heparin and manganase chloride according to the standardized procedures of the Lipid Research Clinics manual."1 LDL cholesterol was calculated using the Friedwald formula.12 Plasma glucose was measured with a glucose oxidase method, and plasma insulin was measured in microunits per milliliter by radioimmunoassay in a diabetes research laboratory.13 Insulin levels were available for subjects seen after November 4, 1985 (n = 216 for fasting plasma insulin, n = 205 for postchallenge plasma insulin). 216 American Journal of Public Health
Two blood pressure readings taken at least 30 seconds apart were obtained with a standard mercury sphygmomanometer after the participants had been seated for 5 minutes. Categorical hypertension was defined as the average of two systolic blood pressure readings equal to or greater than 160 mm Hg; or the average of two diastolic blood pressure readings equal to or greater than 95 mm Hg; or the current use of antihypertensive medication.
Data Analysis The distributions of covariates (age, obesity, alcohol consumption, estrogen use, exercise, smoking, marital status, education, and social class, heart disease riskfactors, total cholesterol, HDL, LDL, triglycerides, systolic and diastolic blood pressures, and fasting and postchallenge plasma glucose and insulin levels) were calculated separately for women working and not working outside the home. Comparisons were made with t tests for continuous variables and with chisquare analyses for categorical variables. Comparisons were adjusted for age by analysis of covariance for continuous variables and by the Mantel-Haenzel Extension Test for categorical variables. Multiple regression analyses were used to examine the independent relation of current work status to lipid and lipoprotein levels, blood pressure, and plasma glucose and insulin levels after adjusting for other potentially confounding physical, sociodemographic, and life-style covariates. All statistical tests were two-tailed.
Among this sample of women, 129 (53.3%) were employed and 113 (46.7%) were not employed outside the home at the time of the interview. Of the former group, 89 were primarily employed as managers, administrators, or business owners, Hollingshead Indexa II and III; 9 were classified as professionals or executives, Hollingshead Index I.14 On average, employed women were 1.7 years younger than unemployed women (t = 3.11, P < .01). As can be seen in Table 1, after adjustment for age, employed women had a significantly higher educational level than unemployed women (P = .04) and were significantly less likely to be currently married (P < .01). Based on the Hollingshead Index of the usual occupation of the head of the household, there was no signifcant difference between employed and unemployed women in social class. Although the differences were not statistically significant, employed women had a lower mean body mass index and waist-hip ratio, consumed less alcohol, were less likely to smoke cigarettes, and were more likely to exercise than unemployed women (see Table 2). Comparisons of employed and unemployed women on other heart disease risk factors are shown in Table 3. Almost all differences favored employed women. After adjustment for age, currently employed women had significantly lower mean total and LDL cholesterol, triglyceride, and postchallenge insulin levels and lower systolic blood pressure than unemployed women. Currently employed women also had a significantly lower rate of categoricaly defined or treated hypertension than unemployed women. Additionally, employed women had lower fasting plasma glucose levels than unemployed women, a difference of borderline statistical significance (P < .07). HDL levels did not differ by employment status.
Hierarchical multiple regression analyses were performed to examine differences in heart disease risk factors between employed and unemployed women after adjusting for the potentially confounding attnbutes as shown in Table 4. After adjustment, employed women had total cholesterol levels that
were
11.8
Index: I = professionals, execaHollingshead =
utives; II managers, small-business owners; III = administrators; IV-X = secretaries, sales, and clerical workers.
February 1992, Vol. 82, No. 2
Employment and Heart Disa in Women
mg/dL lower (P < .05) and fasting plasma glucose levels that were 4.5 mg/dL lower (P < .05) than unemployed women. Currently employed women also had a lower rate of hypertension, systolic blood pressures that were 3.8 mm Hg lower, and postchallenge plasma glucose levels that were 9.5 mg/dL lower than unemployed women, differences that were of clinical but not conventional statistical significance (Ps < .10). All other risk factors also favored the employed women although differences were not statistically significant. Analyses using waist-hip ratio instead of body mass index yielded similar results (data not shown). The possibility that these results were due to a form of self-selection bias known as the healthy worker effect, whereby only the healthiest sought, secured, and maintained jobs, was tested in several ways. Comparisons were made between currently employed and unemployed women on diseases and risk factors ascertained at their baseline enrollment visit between 1972 and 1974. At enrollment, none of these women reported having had a heart attack, heart failure, or a stroke. They would have been 30 to 49 years old at that time-an age before heart or other chronic disease commonly affects the ability to work. Al four women who reported diabetes at baseline were employed at the follow-up (1984 to 1987) visit. Regression analyses restricted to women with "normal" risk factor levels at baseline (i.e., total cholesterol below 225 mg/dL; systolic blood pressure below 140 mm Hg; fasting plasma glucose below 140 mg/dL) indicated that currently employed women had lower risk factors at follow-up (total cholesterol levels 12.9 mg/dL lower [F = 3.75, P < .05], systolic blood pressure 4.1 mm Hg lower [F = 2.90, P < .081, and fasting plasma glucose levels 5.2 mg/dL lower [F = 5.88, P < .01]) than unemployed women. Overall, these data do not support selection bias as an explanation for the more favorable risk factor status among the currently employed women.
Discussion In the present study, women worling outside the home were generally healthier than unemployed women. They had significantly lower total cholesterol and fasting plasma glucose levels than women not currently employed. Differences on all other cardiovascular disease risk factors, although not statistiallly significant, also favored employed women. Furthermore,
February 1992, Vol. 82, No. 2
American Journal of Public Health 217
Kiitz-Sihfstein et al. these differences were not explained by age, obesity, estrogen use, alcohol consumption, cigarette smoking, exercise, marital status, education, or socioeconomic status. The results of the present study are in accord with those of Hazuda et al.,9 who found more favorable lipid levels among employed Mexican-American and nonHispanic White women after adjusting for age, obesity, socioeconomic status, smoking, exercise, alcohol use, and use of oral contraceptives. Hazuda et al.9 also found that fasting and postchallenge plasma glucose levels differed between employed and unemployed Mexican-American women but not between employed and unemployed non-Hispanic White women, a difference that was explained by greater obesity in the former ethnic group.9 In contrast, the present study of upper-middle-class White women, who are on average leaner than other US women,15 found clinically significant differences in plasma glucose levels between employed and unemployed women, independent of obesity. The results ofthe present study are in accord with several studies that demonstrated better self-reported health among employedwomen.16-19 However, they are in contrast to results of the Framingham Heart Study,3'8 which found employment status to have no effect on women's selfreported health. This difference may reflect the Framingham definition of working, according to which any woman who had worked outside her home for more than half her adult life was classified as employed, regardless of her current employment status. The Rancho Bemardo study considered a woman employed only if she was currently employed, the same definition used in other studies.4,9 Two studies have reported that the beneficial effects of working on self-reported health are greater for unmarried women than for married women.20.21 In the present study, where over three quarters of the women were married and there were only nine single unemployed women, adjusting for marital status did not materially alter the results. Differences did not appear to be due to the self-selection bias called the healthy worker effect, whereby only the healthiest are employed outside the home.22 The differences between employed and unemployed women remained even after the analyses were restricted to those who had the most optimal risk factors at enrollment. Women with diabetes, the only chronic disease reported at baseline, were all employed at the time of their follow-up visit. 218 American Journal of Public Health
Differences between employed and unemployed women were not explained by differences in socioeconomic status or educational level. Furthermore, given the homogeneous, upper-middle-class status of this cohort, it is unlikely that the differences reflect differential access to medical care. Employment could be associated with health through other life-style and behavioral factors. Although not statistically significant, differences between employed and unemployed women in obesity, alcohol consumption, cigarette smoking, estrogen use, and regular exercise tended to favor a more healthy life-style among employed women, and adjustment for these attributes reduced the differences in heart disease risk factors between these women
(Table 4). A psychosocial factor could also moderate the relationship between employment status and health. Most of these upper-middle-class women were married and were probably working for job satisfaction rather than financial need. Several studies have found that the association between employment and health is stronger for women who have a more favorable attitude toward their jobs (See Waldron and Herold 198623 for review). A positive job attitude could parallel the perception of control offered by the occupational setting.24 Individuals who feel that what happens to them is the result of factors beyond their control are said to have an external locus of control, whereas those who believe that what happens to them is the result of their own decisions are said to have an internal locus of control325 Those with an internal locus of control are reported to experience less illness,26 less coronary disease,27 less hypertension,28 and less depression9 than those with an external locus of control. In terms of lifestyle factors, those with an internal locus of control are less likely to smoke cigarettes30 and more likely to engage in physical exercise.31 Middle-aged employed women have been found to have a greater sense of personal control over their environment than women who are homemakers or students,24 possibly reflecting their income and job responsibilities. Whatever the mechanism, the present study suggests that upper-middleclass women working outside the home have more favorable heart disease risk factors than unemployed women. Given that almost 80% of the employed women studied were working as professionals, managers, or administrators, these data do not support prior predictions that, as
women attain male professional- or executive-level occupations, they will also acquire male coronary heart disease risk and mortality rates.32 []
Acknowledgments This work was supported by grants AG07181 from the National Institute of Aging and DK301801 from the National Institute of Diabetes and Digestive and Kidney Diseases.
References 1. Thom TJ, Epstein FH, Feldman JJ, Leaverton PE. Trends in total mortality and mortality from heart disease in 26 countries from 1950 to 1978. Int J Epidemiol. 1985;14:510-520. 2. ThomTJ. Cardiovascular disease mortality among United States women. In: Eaker E, Packard B, Wenger NK, Clarkson TB, Tyroler H, eds. Coronary Heart Disease in Women. New York, NY: HaymarketDoyma; 1988:33-41. 3. Haynes SG, Feinleib M. Women, workand coronary heart disease: prospective findings from the Framingham Heart Study. Am JPublic Health. 1980;70:133-141. 4. House JS, Strecher V, Metzner HL, Robbins CA. Occupational stress and health among men and women in the Tecumseh Community Health Study. J Heakh Soc Behav. 1986;27:62-77. 5. National Commission on Working Women. An Overview of Women in the Work Force. Washington, DC: National Commission on Working Women; 1987. 6. US Department of Labor, Bureau of Labor Statistics. Employment and Eawrrur. Vol 35(2). Washington, DC: US Govt Printing Office; December 1978. 7. Mathews KA, Rodin J. Women's changing work roles: impact on health, family, and public policy. Am PsychoL 1989;44:13891393. 8. Haynes SG, Eaker ED, Feinleib M. The effect of employment, family, and job stress on coronary heart disease patterns in women. In: Gold EB, ed. The Changing Risk of Disease in Women: An Epidemiological Approach. Lexington, Mass: DC Health; 1984:37-48. 9. Hazuda HP, Haffner SM, Stern MP, Knapp JA, Eifler CW, Rosenthal M. Employment status and women's protection against coronary heart disease. Am J Epi-
demioL 1986;123:623-640. 10. Hubert HB, Eaker D, Garrison RJ, Castelli WP. Life-style correlates of risk factor change inyoung adults: an eight-year study of coronary heart disease risk factors in the Framingham offspring. Am J EpidemioL
1987;125:812-831. 11. Lipid Research Clinics Program. Manual ofLaboratory Openations. Vol 1.Lipid and L4poproteinAnalysis. 2nd ed. Washington, DC: US Govt Printing Office; 1974. US Dept of Health, Education, and Welfare publication NIH 75-628. 12. Friedwald WJ, Levy RI, Fredrickson DS. Estimation of the concentration of lowdensity lipoprotein cholesterol in plasma without use of the preparative ultracentrifuge. Clin Chem. 1972;18:459-502. 13. Desbuquois B, Ausbach GD. Use of pohy-
Februaxy 1992, Vol. 82, No. 2
Empkymnt and Heart Disa in Women ethylene glycol to separate free and antibody-bound peptide hormones in radioimmunoassay. J Clin Endocrinol Metab. 1971;33:732-738. 14. HolingsheadAB. Two-Factor Indec ofSocial Posito Privately published; 1957. 15. Barrett-Connor E. The prevalence of diabetes mellitus in an adult community as determined by history of fasting hyperglycemia. Am JEpidemioL 1980;111:705-712. 16. Adelman PK, Antonucci TC, Crohan SE, Coleman LM. A causal analysis ofemployment and health in midlife women. Women Health 1990;16:5-20. 17. Jennings S, Mazaik C, McKinlay S. Women and work: an investigation of the association between health and employment status in middle-agedwomen. Soc Sci MeA 1984;19:423-431. 18. Verbrugge L. Role burdens and physical health of women and men. Women Health. 1986;11:47-77. 19. Waldron I. Employment and women's health: an analysis of causal relationships.
February 1992, Vol. 82, No. 2
Int JHealth Serv. 1980;10:435-454. 20. Waldron I, Jacobs J. Effects of labor force participation on women's health: new evidence from a longitudinal study. J Occup MeL 1988;30:977-983. 21. Repetti RL, Mathews KA, Waldron I. Employment and women's health: effects of paid employment on women's mental and physical health. Am Psychol. 1989;11: 1394-1401. 22. McMichael AJ, Haynes SG, Tyroler HA. Observations of the evaluation of occupational mortality data. J Occup Med. 1975;17:128-131. 23. Waldron I, Herold J. Employment, attitudes toward employment and women's health. Women Heath 1986;11:79-98. 24. Erdwins CJ, Mellinger JC. Midlife women: relation of age and role to personality. J Pers Soc PsychoL 1984;47:390-395. 25. RotterJB. Generalized expectancies for internal versus external control of reinforcement. Psychol Monogr. 1966;80(1, whole no. 609).
26. Kobasa SC. Stressful live events, personality and health: an inquiry into hardiness. JPers Soc PsychoL 1979;37:1-11. 27. Cromwell RL, Butterfield EC, Brayfield FM, Curry JL. Acute Myocardial Infarction. Reaction and Recovery. St. Louis, Mo: CV Mosby; 1977. 28. Naditch MP. Locus of control, relative discontent and hypertension. Soc Psychiatry. 1974;9:111-117. 29. Lefcourt HM. Locus of Controb Cwrent Trends in Theory and Research Hillsdale, NJ: Lawrence Erlbaum; 1976. 30. Coan RW. Personality variables associated with cigarette smoking. J Pers Soc PsychoL 1973;26:86-104. 31. Walker TG. Behavior of temporary members in small groups. J Appl Psychol. 1973;58:144-146. 32. Baruch GK, Biener L, Barnett RC. Women and gender in research on work and family stress. Am Psycho 1987;42: 130-136.
American Joumal of Public Health 219
...I........I.I.I.I...-.-.-
..Im -1- MEN
Donna Kritz-Silverstein, PhD, Deborah L. Barrett-Connor, MD
Introduction Heart disease is the leading cause of death among both men and women.12 In men, risk of heart disease is related to employment.3'4 However, although more and more women have been entering the labor force in recent years,-7 few studies have examined employment and heart disease risk factors in women, and their findings have been inconsistent.3,48-_1''. Among young women in the Framingham Offspring Study, homemakers and those employed outside the home were compared and showed no significant differences in blood pressure, total cholesterol, high-density lipoprotein (HDL) level, or low-density lipoprotein (LDL) level over an 8-year period. '° In contrast, Hazuda et al.9 found highly significant differences in HDL and in ratio of HDL to total cholesterol, triglycerides, and fasting and postchallenge plasma glucose favoring employed women over homemakers. These differences were not explained by age, socioeconomic status, obesity, exercise, smoking, alcohol consumption, or use of estrogen. We studied the association of employment status and heart disease risk factors in middle-aged White women. We examined differences between employed and nonemployed women in blood pressure, lipid and lipoprotein levels, and fasting and postchallenge plasma glucose and insulin levels before and after adjusting for potentially confounding physical and lifestyle covariates.
Methods The population consisted of women who were initially enrolled in the Rancho Bernardo Heart and Chronic Disease Sur-
Wingard, PhD,
and Elizabeth
vey between 1972 and 1974 and who attended a follow-up clinic visit between 1984 and 1987; 84% of surviving women aged 40 and older responded. This report is based on the 242 women aged 40 through 59 at the follow-up visit who had fasted the requested 12 hours and were not currently taking lipid-lowering medications. This age group was chosen for analysis because there were too few women over age 59 who were still working. Only one woman was excluded for not fasting the requested 12 hours, and three women were excluded because they were using lipid-lowering medications.
Data Collection A standardized interview was used to obtain information on current employment status, marital status, cigarette smoking, alcohol consumption (number of drinks per week of beer, wine, or liquor converted to milliliters of alcohol per week), and exercise (whether subjects exercised three or more times per week). Reported current use of estrogen and other medications was confirmed by prescriptions or pill containers brought to the clinic for that purpose. In the clinic, height (meters), weight (kilograms), and waist and hip circumferences (centimeters) were measured with The authors are with the Department of Community and Family Medicine, Division of Epidemiology, at the University of California, San
Diego. Requests for reprints should be sent to Elizabeth Barrett-Connor, MD, Division of Epidemiology, Department of Community and Family Medicine, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 920930607. This paper was submitted to the journal January 31, 1991, and accepted with revisions
September 16, 1991.
American Journal of Public Health 215
Keiz-Sivertein et al.
Results
the participants in light clothing and without shoes. Body mass index (weight/ height2) and waist-hip ratio (waist circumference/hip circumference x 100) were used to estimate obesity and central
adiposity, respectively. An oral glucose tolerance test with a 75-g glucose load was performed between 7 AM and 11 AM after a 12-hour fast. Blood was obtained by venipuncture before and 2 hours after the glucose challenge. Lipids and lipoproteins were measured in a Lipid Research Clinics laboratory under the continuous standardization program of the Centers for Disease Control in Atlanta, Ga. Fasting plasma total cholesterol and triglyceride levels were measured by enzymatic techniques with an ABA-200 biochromatic analyzer (Abbott Laboratories, Irving, Tex), a highperformance cholesterol reagent (No. 236691, Boehringer-Mannheim Diagnostics, Indianapolis, Ind), and a triglyceride agent (No. 6097, Abbot Laboratories). HDL cholesterol was measured by precipitating the other lipoproteins with heparin and manganase chloride according to the standardized procedures of the Lipid Research Clinics manual."1 LDL cholesterol was calculated using the Friedwald formula.12 Plasma glucose was measured with a glucose oxidase method, and plasma insulin was measured in microunits per milliliter by radioimmunoassay in a diabetes research laboratory.13 Insulin levels were available for subjects seen after November 4, 1985 (n = 216 for fasting plasma insulin, n = 205 for postchallenge plasma insulin). 216 American Journal of Public Health
Two blood pressure readings taken at least 30 seconds apart were obtained with a standard mercury sphygmomanometer after the participants had been seated for 5 minutes. Categorical hypertension was defined as the average of two systolic blood pressure readings equal to or greater than 160 mm Hg; or the average of two diastolic blood pressure readings equal to or greater than 95 mm Hg; or the current use of antihypertensive medication.
Data Analysis The distributions of covariates (age, obesity, alcohol consumption, estrogen use, exercise, smoking, marital status, education, and social class, heart disease riskfactors, total cholesterol, HDL, LDL, triglycerides, systolic and diastolic blood pressures, and fasting and postchallenge plasma glucose and insulin levels) were calculated separately for women working and not working outside the home. Comparisons were made with t tests for continuous variables and with chisquare analyses for categorical variables. Comparisons were adjusted for age by analysis of covariance for continuous variables and by the Mantel-Haenzel Extension Test for categorical variables. Multiple regression analyses were used to examine the independent relation of current work status to lipid and lipoprotein levels, blood pressure, and plasma glucose and insulin levels after adjusting for other potentially confounding physical, sociodemographic, and life-style covariates. All statistical tests were two-tailed.
Among this sample of women, 129 (53.3%) were employed and 113 (46.7%) were not employed outside the home at the time of the interview. Of the former group, 89 were primarily employed as managers, administrators, or business owners, Hollingshead Indexa II and III; 9 were classified as professionals or executives, Hollingshead Index I.14 On average, employed women were 1.7 years younger than unemployed women (t = 3.11, P < .01). As can be seen in Table 1, after adjustment for age, employed women had a significantly higher educational level than unemployed women (P = .04) and were significantly less likely to be currently married (P < .01). Based on the Hollingshead Index of the usual occupation of the head of the household, there was no signifcant difference between employed and unemployed women in social class. Although the differences were not statistically significant, employed women had a lower mean body mass index and waist-hip ratio, consumed less alcohol, were less likely to smoke cigarettes, and were more likely to exercise than unemployed women (see Table 2). Comparisons of employed and unemployed women on other heart disease risk factors are shown in Table 3. Almost all differences favored employed women. After adjustment for age, currently employed women had significantly lower mean total and LDL cholesterol, triglyceride, and postchallenge insulin levels and lower systolic blood pressure than unemployed women. Currently employed women also had a significantly lower rate of categoricaly defined or treated hypertension than unemployed women. Additionally, employed women had lower fasting plasma glucose levels than unemployed women, a difference of borderline statistical significance (P < .07). HDL levels did not differ by employment status.
Hierarchical multiple regression analyses were performed to examine differences in heart disease risk factors between employed and unemployed women after adjusting for the potentially confounding attnbutes as shown in Table 4. After adjustment, employed women had total cholesterol levels that
were
11.8
Index: I = professionals, execaHollingshead =
utives; II managers, small-business owners; III = administrators; IV-X = secretaries, sales, and clerical workers.
February 1992, Vol. 82, No. 2
Employment and Heart Disa in Women
mg/dL lower (P < .05) and fasting plasma glucose levels that were 4.5 mg/dL lower (P < .05) than unemployed women. Currently employed women also had a lower rate of hypertension, systolic blood pressures that were 3.8 mm Hg lower, and postchallenge plasma glucose levels that were 9.5 mg/dL lower than unemployed women, differences that were of clinical but not conventional statistical significance (Ps < .10). All other risk factors also favored the employed women although differences were not statistically significant. Analyses using waist-hip ratio instead of body mass index yielded similar results (data not shown). The possibility that these results were due to a form of self-selection bias known as the healthy worker effect, whereby only the healthiest sought, secured, and maintained jobs, was tested in several ways. Comparisons were made between currently employed and unemployed women on diseases and risk factors ascertained at their baseline enrollment visit between 1972 and 1974. At enrollment, none of these women reported having had a heart attack, heart failure, or a stroke. They would have been 30 to 49 years old at that time-an age before heart or other chronic disease commonly affects the ability to work. Al four women who reported diabetes at baseline were employed at the follow-up (1984 to 1987) visit. Regression analyses restricted to women with "normal" risk factor levels at baseline (i.e., total cholesterol below 225 mg/dL; systolic blood pressure below 140 mm Hg; fasting plasma glucose below 140 mg/dL) indicated that currently employed women had lower risk factors at follow-up (total cholesterol levels 12.9 mg/dL lower [F = 3.75, P < .05], systolic blood pressure 4.1 mm Hg lower [F = 2.90, P < .081, and fasting plasma glucose levels 5.2 mg/dL lower [F = 5.88, P < .01]) than unemployed women. Overall, these data do not support selection bias as an explanation for the more favorable risk factor status among the currently employed women.
Discussion In the present study, women worling outside the home were generally healthier than unemployed women. They had significantly lower total cholesterol and fasting plasma glucose levels than women not currently employed. Differences on all other cardiovascular disease risk factors, although not statistiallly significant, also favored employed women. Furthermore,
February 1992, Vol. 82, No. 2
American Journal of Public Health 217
Kiitz-Sihfstein et al. these differences were not explained by age, obesity, estrogen use, alcohol consumption, cigarette smoking, exercise, marital status, education, or socioeconomic status. The results of the present study are in accord with those of Hazuda et al.,9 who found more favorable lipid levels among employed Mexican-American and nonHispanic White women after adjusting for age, obesity, socioeconomic status, smoking, exercise, alcohol use, and use of oral contraceptives. Hazuda et al.9 also found that fasting and postchallenge plasma glucose levels differed between employed and unemployed Mexican-American women but not between employed and unemployed non-Hispanic White women, a difference that was explained by greater obesity in the former ethnic group.9 In contrast, the present study of upper-middle-class White women, who are on average leaner than other US women,15 found clinically significant differences in plasma glucose levels between employed and unemployed women, independent of obesity. The results ofthe present study are in accord with several studies that demonstrated better self-reported health among employedwomen.16-19 However, they are in contrast to results of the Framingham Heart Study,3'8 which found employment status to have no effect on women's selfreported health. This difference may reflect the Framingham definition of working, according to which any woman who had worked outside her home for more than half her adult life was classified as employed, regardless of her current employment status. The Rancho Bemardo study considered a woman employed only if she was currently employed, the same definition used in other studies.4,9 Two studies have reported that the beneficial effects of working on self-reported health are greater for unmarried women than for married women.20.21 In the present study, where over three quarters of the women were married and there were only nine single unemployed women, adjusting for marital status did not materially alter the results. Differences did not appear to be due to the self-selection bias called the healthy worker effect, whereby only the healthiest are employed outside the home.22 The differences between employed and unemployed women remained even after the analyses were restricted to those who had the most optimal risk factors at enrollment. Women with diabetes, the only chronic disease reported at baseline, were all employed at the time of their follow-up visit. 218 American Journal of Public Health
Differences between employed and unemployed women were not explained by differences in socioeconomic status or educational level. Furthermore, given the homogeneous, upper-middle-class status of this cohort, it is unlikely that the differences reflect differential access to medical care. Employment could be associated with health through other life-style and behavioral factors. Although not statistically significant, differences between employed and unemployed women in obesity, alcohol consumption, cigarette smoking, estrogen use, and regular exercise tended to favor a more healthy life-style among employed women, and adjustment for these attributes reduced the differences in heart disease risk factors between these women
(Table 4). A psychosocial factor could also moderate the relationship between employment status and health. Most of these upper-middle-class women were married and were probably working for job satisfaction rather than financial need. Several studies have found that the association between employment and health is stronger for women who have a more favorable attitude toward their jobs (See Waldron and Herold 198623 for review). A positive job attitude could parallel the perception of control offered by the occupational setting.24 Individuals who feel that what happens to them is the result of factors beyond their control are said to have an external locus of control, whereas those who believe that what happens to them is the result of their own decisions are said to have an internal locus of control325 Those with an internal locus of control are reported to experience less illness,26 less coronary disease,27 less hypertension,28 and less depression9 than those with an external locus of control. In terms of lifestyle factors, those with an internal locus of control are less likely to smoke cigarettes30 and more likely to engage in physical exercise.31 Middle-aged employed women have been found to have a greater sense of personal control over their environment than women who are homemakers or students,24 possibly reflecting their income and job responsibilities. Whatever the mechanism, the present study suggests that upper-middleclass women working outside the home have more favorable heart disease risk factors than unemployed women. Given that almost 80% of the employed women studied were working as professionals, managers, or administrators, these data do not support prior predictions that, as
women attain male professional- or executive-level occupations, they will also acquire male coronary heart disease risk and mortality rates.32 []
Acknowledgments This work was supported by grants AG07181 from the National Institute of Aging and DK301801 from the National Institute of Diabetes and Digestive and Kidney Diseases.
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