LEUKOCYTE COUNT AND CARDIOVASCULAR RISK FACTOR Deborah D. Ingram, PhD, and Richard F. Gillum, MD Hyattsville, Maryland
In view of the growing evidence for leukocyte count as an important cardiovascular risk factor, data from the first National Health and Nutrition Examination Survey (NHANES I) were examined to determine the association of leukocyte count with a number of other cardiovascular risk factors. Complete data were available for 5586 persons. Multiple linear regression analyses revealed hemoglobin concentration and height in white male nonsmokers and hemoglobin, cigarettes/day, and pulse rate in white male smokers were associated with leukocyte count. In white female nonsmokers, age, pulse rate, systolic blood pressure, height, and uric acid concentration were associated with leukocyte count. In white female smokers, hemoglobin, cigarettes/day, pulse rate, and height were associated with leukocyte count. However, associated variables explained only 8% of the variation in leukocyte count. Other measured risk factors were not associated with leukocyte count. Future analyses of leukocyte count and cardiovascular disease should control for hemoglobin concentration and pulse rate in addition to smoking, blood pressure, and cholesterol. (J NatI Med Assoc. 1992;84:1041-1043.) Key words *leukocyte count * cholesterol-blood * blood pressure * smoking * hemoglobins
Several studies have shown leukocyte count to be a risk factor for coronary heart disease incidence and From the National Center for Health Statistics, Office of Analysis and Epidemiology, Hyattsville, Maryland. Requests for reprints should be addressed to Dr Deborah D. Ingram, National Center for Health Statistics, Office of Analysis and Epidemiology, 6525 Belcrest Rd, Rm 1070, Hyattsville, MD 20782. JOURNAL OF THE NATIONAL MEDICAL ASSOCIATION, VOL. 84, NO. 12
mortality, and for all causes of mortality.1 2 However, only a few reports have investigated risk factors other than smoking that affect leukocyte count in healthy adults.3-6 In view of the growing evidence for leukocyte count as an important cardiovascular risk factor, data from a representative sample of the US population were examined to determine associations of leukocyte count with a large number of established and putative cardiovascular risk factors. Such information may be of value in elucidating reported associations of leukocyte count with morbidity and mortality.
METHODS The association of a large number of cardiovascular risk factors with leukocyte count was examined for white and black persons who comprised the study population for the first National Health and Nutrition Examination Survey (NHANES I). Because of the strong associations of smoking and race with leukocyte count reported for this sample,6 analyses are presented separately for nonsmokers and smokers by race. Nonsmokers were defined as those who never smoked and former smokers. Results also are presented by sex for whites, but small numbers necessitated combining black males and females. The NHANES I collected data on a stratified multistage national probability sample of the civilian noninstitutionalized population of the United States from 1971 to 1975. A subsample of persons aged 25 to 74 years received a detailed medical examination. This examination sample had a response rate of 71 %. Details of the plan, sampling, operation, and response have been published elsewhere.5-8 Demographic, medical history, and behavioral information were collected by household interviews prior to the medical examinations. Medical examinations were carried out in mobile examination centers. Blood samples were obtained, and total leukocyte count was determined in duplicate at the examination site on a Coulter Fn.6 Multiple linear regression was used to relate selected 1041
LEUKOCYTES & CARDIOVASCULAR RISK FACTORS
TABLE. REGRESSION COEFFICIENTS AND MULTIPLE R2 FROM MODELS RELATING LEUKOCYTE COUNT (THOUSANDS/mm3) AND SELECTED CARDIOVASCULAR RISK FACTORS AMONG PERSONS AGED 25-74 YEARS FROM NHANES I Black Males and White Males White Females Females B SE B SE B SE Nonsmokers Age (years) -.008 .007 -.019* .005 -.009 .010 - .996* Sex .367 Hemoglobin (mg/100 mL) .266* .057 .035 .047 .245* .095 Pulse rate (beat/minute) .007 .005 .017* .004 .018 .010 Weight (kg) .006 .005 .002 .005 .008 .010 Cholesterol (mg/dL) .002 .001 -.000 .001 -.003 .002 Systolic blood pressure (mm Hg) .006 .003 .007t .003 .009t .004 Height (cm) - 033* -.022t .009 .009 -.007 .018 Uric acid (mg/100 mL) .000 .040 .189* .048 .125 .073 Diabetes (yes = 1) - .048 - .255 .265 .243 .252 .527 Constant 5.096 9.858 1.859 n 1341 1814 349 R2 .06 .06 .11
Smokers Age (years) Sex Cigarettes/day Hemoglobin (mg/100 mL) Pulse rate (beat/minute) Weight (kg) Cholesterol (mg/dL) Systolic blood pressure (mm Hg) Height (cm) Uric acid (mg/i 00 mL) Diabetes (yes= 1) Constant n
R2
-.007
.006
-.020t
.009
.014* .242* .015t -.004 .001 .002 -.014 .002 - .268 6.006 936 .05
.004 .070 .007 .007 .002 .003 .012 .062 .329
.028* .191 * .017* .011 .003 .004 -.015 - .048 .343 5.036 829 .07
.007 .066 .006 .006 .002 .005 .015 .075 .439
-.000 .321 .021 .086 - .001 .015 .006t -.005 -.035 - .030 .431 9.500 317 .06
.014 .561 .012 .119 .012 .009 .003 .007 .020 .101 .577
Abbreviations: B = regression coefficient and SE = standard error. *P
In view of the growing evidence for leukocyte count as an important cardiovascular risk factor, data from the first National Health and Nutrition Examination Survey (NHANES I) were examined to determine the association of leukocyte count with a number of other cardiovascular risk factors. Complete data were available for 5586 persons. Multiple linear regression analyses revealed hemoglobin concentration and height in white male nonsmokers and hemoglobin, cigarettes/day, and pulse rate in white male smokers were associated with leukocyte count. In white female nonsmokers, age, pulse rate, systolic blood pressure, height, and uric acid concentration were associated with leukocyte count. In white female smokers, hemoglobin, cigarettes/day, pulse rate, and height were associated with leukocyte count. However, associated variables explained only 8% of the variation in leukocyte count. Other measured risk factors were not associated with leukocyte count. Future analyses of leukocyte count and cardiovascular disease should control for hemoglobin concentration and pulse rate in addition to smoking, blood pressure, and cholesterol. (J NatI Med Assoc. 1992;84:1041-1043.) Key words *leukocyte count * cholesterol-blood * blood pressure * smoking * hemoglobins
Several studies have shown leukocyte count to be a risk factor for coronary heart disease incidence and From the National Center for Health Statistics, Office of Analysis and Epidemiology, Hyattsville, Maryland. Requests for reprints should be addressed to Dr Deborah D. Ingram, National Center for Health Statistics, Office of Analysis and Epidemiology, 6525 Belcrest Rd, Rm 1070, Hyattsville, MD 20782. JOURNAL OF THE NATIONAL MEDICAL ASSOCIATION, VOL. 84, NO. 12
mortality, and for all causes of mortality.1 2 However, only a few reports have investigated risk factors other than smoking that affect leukocyte count in healthy adults.3-6 In view of the growing evidence for leukocyte count as an important cardiovascular risk factor, data from a representative sample of the US population were examined to determine associations of leukocyte count with a large number of established and putative cardiovascular risk factors. Such information may be of value in elucidating reported associations of leukocyte count with morbidity and mortality.
METHODS The association of a large number of cardiovascular risk factors with leukocyte count was examined for white and black persons who comprised the study population for the first National Health and Nutrition Examination Survey (NHANES I). Because of the strong associations of smoking and race with leukocyte count reported for this sample,6 analyses are presented separately for nonsmokers and smokers by race. Nonsmokers were defined as those who never smoked and former smokers. Results also are presented by sex for whites, but small numbers necessitated combining black males and females. The NHANES I collected data on a stratified multistage national probability sample of the civilian noninstitutionalized population of the United States from 1971 to 1975. A subsample of persons aged 25 to 74 years received a detailed medical examination. This examination sample had a response rate of 71 %. Details of the plan, sampling, operation, and response have been published elsewhere.5-8 Demographic, medical history, and behavioral information were collected by household interviews prior to the medical examinations. Medical examinations were carried out in mobile examination centers. Blood samples were obtained, and total leukocyte count was determined in duplicate at the examination site on a Coulter Fn.6 Multiple linear regression was used to relate selected 1041
LEUKOCYTES & CARDIOVASCULAR RISK FACTORS
TABLE. REGRESSION COEFFICIENTS AND MULTIPLE R2 FROM MODELS RELATING LEUKOCYTE COUNT (THOUSANDS/mm3) AND SELECTED CARDIOVASCULAR RISK FACTORS AMONG PERSONS AGED 25-74 YEARS FROM NHANES I Black Males and White Males White Females Females B SE B SE B SE Nonsmokers Age (years) -.008 .007 -.019* .005 -.009 .010 - .996* Sex .367 Hemoglobin (mg/100 mL) .266* .057 .035 .047 .245* .095 Pulse rate (beat/minute) .007 .005 .017* .004 .018 .010 Weight (kg) .006 .005 .002 .005 .008 .010 Cholesterol (mg/dL) .002 .001 -.000 .001 -.003 .002 Systolic blood pressure (mm Hg) .006 .003 .007t .003 .009t .004 Height (cm) - 033* -.022t .009 .009 -.007 .018 Uric acid (mg/100 mL) .000 .040 .189* .048 .125 .073 Diabetes (yes = 1) - .048 - .255 .265 .243 .252 .527 Constant 5.096 9.858 1.859 n 1341 1814 349 R2 .06 .06 .11
Smokers Age (years) Sex Cigarettes/day Hemoglobin (mg/100 mL) Pulse rate (beat/minute) Weight (kg) Cholesterol (mg/dL) Systolic blood pressure (mm Hg) Height (cm) Uric acid (mg/i 00 mL) Diabetes (yes= 1) Constant n
R2
-.007
.006
-.020t
.009
.014* .242* .015t -.004 .001 .002 -.014 .002 - .268 6.006 936 .05
.004 .070 .007 .007 .002 .003 .012 .062 .329
.028* .191 * .017* .011 .003 .004 -.015 - .048 .343 5.036 829 .07
.007 .066 .006 .006 .002 .005 .015 .075 .439
-.000 .321 .021 .086 - .001 .015 .006t -.005 -.035 - .030 .431 9.500 317 .06
.014 .561 .012 .119 .012 .009 .003 .007 .020 .101 .577
Abbreviations: B = regression coefficient and SE = standard error. *P
