Factors associated with hypertension in Nigerian civil servants

PREVENTIVE

MEDICINE

Factors

21, 71&722 (1992)

Associated

with Hypertension Civil Servants’

in Nigerian

CLAREANN H. BUNKER, PH.D., *2 FLORA A. UKOLI, M.B.B.S.,? MARTIN U. NWANKWO, M.B.B.S.,‘F3 JACKSON A. OMENE, M.D.,t4 GLENN W. CURRIER, M.D.,* LINDA HOLIFIELD-KENNEDY,~ DONALD T. FREEMAN,* EMANUEL N. VERGIS, M.D.,* LAN LAN L. YEH, PH.D.,* AND LEWIS H. KULLER, M.D., DR.P.H.* *Graduate

School of Public Health and SSchool of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania; and fUniversity of Benin Teaching Hospital, Benin City, Nigeria

Background. Study of hypertension in segments of West African populations in transition toward Westernization may lead to better understanding of the high risk for hypertension among Westernized blacks. Methods. Five hundred fifty-nine urban civil servants, ages 25-54, were recruited from six ministries of Bendel State, Nigeria. Blood pressure, physical measurements, urinary protein and glucose, fasting blood glucose, and demographic data were collected at the workplace. Subjects were classified as senior staff (professionals or administrators) or junior staff (nonadministrators). Results. Among 172 male senior staff, the age-adjusted rate of hypertension (diastolic blood pressure 390 mm Hg, systolic blood pressure 2140 mm Hg, or on an antihypertensive medication) was 43% and occurrence rose dramatically from 21 to 63% across age groups 25-34 to 45-54, respectively. Among 266 male junior staff, the age-adjusted rate of hypertension was 23%, and occurrence did not rise with age. Logistic regression showed that body mass index (kg/m’), age, alcohol drinking, and being senior staff were all independently related to hypertension in men. On the other hand, the age-adjusted rate of hypertension in 121 women was 20% and was significantly related only to body mass index. Conrlusion. Male urban civil servants appeared to have a risk for hypertension similar to that of U.S. black males. Age, body mass index, alcohol drinking, and other unidentified factors related to higher socioeconomic status were strong determinants of hypertension in this population. 0 1592 Academic Press, Inc.

INTRODUCTION

In 1929, Donnison (1) found no cases of hypertension or arteriosclerosis among 1,800 admissions to a rural Kenyan hospital. In later studies in sub-Saharan Africa, hypertension remained absent or very rare in primitive, nomadic tribes (2-5) and in rural, pastoral, or subsistence agricultural communities (6-9). These findings, a sharp contrast to the very high prevalence of hypertension among African ’ This project was supported in part by BRSG 2SO7 RR05451-26 and 2SO7 RR05451-27, awarded by the Biomedical Research Support Grant Program, Division of Research Resources, National Institutes of Health. ’ To whom reprint requests should be addressed al Department of Epidemiology, University of Pittsburgh, 130 DeSoto Street, Pittsburgh, PA 15261. 3 Present address: Department of Pediatrics, Graduate Medical Education, Inc., Michigan State University, East Lansing, MI. 4 Present address: Department of Pediatrics, Woodhull Hospital, Brooklyn, NY. 710 0091-7435192 $5.00 Copyright 0 1992 by Academic Press. Inc. All rights of reproduction in any form reserved.

HYPERTENSION

IN NIGERIANS

711

Americans (IO), have created an impression, which persists today, that African blacks have a lower risk for hypertension than U.S. or other Westernized blacks. This has led Grim and colleagues (11) to hypothesize that the high risk in American blacks is due to genetic selection for the ability to conserve salt among those who were able to survive the severe diarrhea experienced during migration to America on slave ships. This ability to conserve salt could lead to liability for hypertension under conditions of high salt intake. However, since the 1950s African studies in rural populations and a number of urban populations have found high hypertension prevalence rates similar to rates in U.S. whites (12-14) or even higher rates similar to rates in U.S. blacks (15-19). These studies suggest that African blacks and U.S. blacks may have a similar underlying risk for hypertension. This risk is being expressed as higher prevalence of hypertension, as these African societies, or segments of these societies, evolve toward a more Westernized lifestyle. Comparisons of urban and rural African populations suggest that higher relative weight (20, 21), higher sodium intake (20-24), and lower potassium intake (24) are factors related to the higher blood pressure observed in urban populations. Stress is also suspected to be important (22, 24). West Africa was the ancestral origin of about 75% of the slaves coming to America, including about 25% from Nigeria alone (25). Studies of factors related to hypertension in the dynamic settings of Nigeria may lead to a better understanding of the emerging health burden of hypertension in Nigeria and West Africa, as well as the entrenched burden of hypertension among U.S. blacks. A substantial bureaucracy has developed in Nigeria over the past few decades, primarily in urban areas. This segment of the population, while still very distinctly Nigerian in lifestyle, is much closer to having a Westernized style of living than the great majority of the Nigerian population, which continues to eke out a living by subsistence farming and petty trading. This study was carried out to measure factors related to hypertension in a relatively healthy, urban, working population of civil servants in Nigeria. METHODS

The study was carried out in Benin City, the capital of Bendel State in southcentral Nigeria. The population of the city was estimated to be 250,000 to 500,000. Civil servants stationed in the city offices of the Bendel State Ministries of Commerce and Industry, Lands and Surveys, Social Development, Information and Culture, Education, and the National Police Force participated in this study in the summers of 1987and 1988. Permission to conduct the study was obtained from the head of each ministry. Each head then invited his/her staff to volunteer to participate. Each morning of the study, a messenger was assigned to recruit all workers present in a specific work area. All measurements were taken in a conference room in each ministry. A questionnaire regarding age, sex, tribe, job grade, job title, education, years of residence in urban or rural setting, current pregnancy, number of bottles of beer per week, number of drinks of palm wine or other spirits per week, and number of cigarettes per day was administered to each subject. Women who reported being pregnant were excluded from the study. After at least 5 min of quiet sitting, blood pressure (first and fifth Korotkoff

712

BUNKER

ET

AL.

sounds) was measured three times by an observer with a mercury sphygmomanometer (Baumanometer, W.A. Baum, Copiague, NY) using either a standard (25-35 cm) or large (3347 cm) cuff, depending on arm size. Observers (University of Pittsburgh medical students) were certified according to the Multiple Risk Factor Intervention Trial protocol (26). The average of the latter two readings was used in this study. Height and weight were measured in light clothing without shoes. Subjects participating in 1988 were instructed to fast overnight and return the following morning, at which time 10 ml of venous blood was drawn using a plain vacuum tube, and a spot sample of urine was collected. From the fresh blood specimen, blood glucose was measured with a glucometer (Glucoscan, Lifescan, Mountain View, CA), sickle cell trait status was determined using a test based on differential solubility of hemoglobin S (Sicklequik, Organon Teknika, Durham, NC), and glucose-6-phosphate dehydrogenase deficiency was measured using a brilliant cresyl blue dye-based test (Sigma Diagnostics, St. Louis, MO). Fresh urine was tested for protein and glucose using a dipstick (Multistix, Miles, Inc. Elkhart, IN). Microalbuminuria was assessed using a qualitative immunoassay (Albusure, Cambridge Life Sciences, Cambridge, England) that detects urinary concentrations greater than 0.03 g/liter with a sensitivity of 81.8% and a specificity of 94.8% (27). Descriptive statistics, t tests, x2 tests, and correlations were carried out using the Statistical Package for the Social Sciences, PC version (28). The BMDP stepwise logistic regression module (BMDPLR 1990version, VAX/VMS) was used for logistic regression analysis (29). Using the criteria of the National Health and Nutrition Examination Survey, 19761980 (NHANES II) (lo), definite hypertension was defined as systolic blood pressure 3160 mm Hg or diastolic blood pressure 395 mm Hg, or taking blood pressure medication. Borderline hypertension was defined as systolic blood pressure 2 140 and < 160 mm Hg or diastolic blood pressure 290 and <95 mm Hg. For most analyses, definite and borderline were combined and referred to simply as hypertension. Direct age adjustment of hypertension rates was based on the age distribution of the total group of subjects. In Nigeria, civil servants are categorized by job grade into senior staff (job grades 7-16, administrative and professional staff,) or junior staff (job grades l-6, clerical and nonskilled staff). Salary increases by job grade in a stepwise manner. Senior and junior staff designations, which are important descriptors of socioeconomic status within the country, were used in the analyses. RESULTS

There were 559 subjects ages 25-54 years, 187 in 1987 and 372 in 1988. All subjects were Nigerian blacks. There were 438 men and 121 women. The mean age for men was higher than that for women, 37.8 and 34.9 years, respectively (P < 0.001). Descriptive data are shown in Table 1. Blood pressure was significantly higher among men, 127.9/82.2 (systolic/diastolic, mm Hg) than among women, 116.4/75.4, ANOVA adjusted for age, P < 0.001. Systolic and diastolic blood pressures were significantly correlated with age among men (r = 0.30, r = 0.24, respectively; P < 0.001). A similar trend was seen in women (Table 1), but the number of women over age 44 (n = 9) was very small. Men and women were

HYPERTENSION

713

IN NIGERIANS

TABLE 1 MEAN BLOOD PRESSURE AND BODY MASS INDEX OF CIVIL SERVANTS, BENIN CITY, NIGERIA, 1987-1988 Males

Females

Systolic blood pressure (mm Hg)

Diastolic blood pressure (mm Hg)

Body mass index (kg/m*) 21.6 22.9 24.4 22.8 3.9 Senior staff 22.6 23.8 25.7 24.5 4.4 Junior staff 21.5 22.3 20.9 21.7 3.1

Age

n

25-34 35-44 45-54 Total SD

158 178 102 438

123.1 127.7 135.7 127.9 17.7

79.1 82.3 86.6 82.2 12.6

25-34 35-44 45-54 Total SD

22 76 74 172

121.5 131.6 139.7 133.8 19.8

79.2 85.0 89.1 86.1 13.4

25-34 35-44 45-54 Total SD

136 102 28 266

123.3 124.9 125.2 124.1 15.1

79.1 80.3 79.8 79.6 11.3

Systolic blood pressure (mm Hg)

Diastolic blood pressure (mm Hg)

Body mass index (kdd

62 50 9 121

114.2 117.0 128.6 116.4 15.1

74.8 74.8 83.0 75.4 11.3

24.1 25.4 27.4 24.9 4.3

10 25 6 41

115.3 116.2 125.0 117.2 15.4

76.3 74.4 81.3 75.9 10.9

24.1 25.5 27.5 25.5 4.2

52 25 3 80

113.9 117.8 135.7 116.0 15.1

74.6 75.2 86.3 75.2 11.5

24.2 25.3 27.0 24.6 4.3

n

similar in weight, but men were 3.6 inches taller, resulting in a significantly lower body mass index (BMI, kg/m2) for men (22.8) than for women (24.9), P < 0.001. Correlations of BMI with systolic and diastolic blood pressure for men were 0.33 and 0.32, respectively (P < 0.001); corresponding values for women were 0.44 and 0.44 (P < 0.001). Sixty-nine percent of men (300/435) and 77% (93021) of women reported secondary or higher education, including 25% (109/435) of the men and 14% (17/121) of the women who had attended a university or technical school. Sixty-five percent (284/437) of men and 37% (44/120) of women reported drinking alcohol. Cigarette smoking was reported by 20% (87/436) of the men and none of the women. The occurrence of borderline and definite hypertension is shown in Table 2. Total hypertension in men increased by age group from 20% for ages 25-34 to 52% for ages 45-54. Of these, 9% (13/150) were treated and only one was under control. Among women, occurrence of hypertension was 17% (20/121), and 5% (l/20) were treated and under control. The age-adjusted rate of hypertension among men was 33% compared with 20% among women. Large differences in the occurrence of hypertension between male junior staff and senior staff were observed (Table 2). Among junior staff, the age-adjusted rate of hypertension was 23%. The occurrence of hypertension did not increase significantly across age groups, with hypertension present in 20% at ages 25-34,24% at ages 35-44, and 25% at ages 45-54. There were 9% with definite hypertension. Among senior staff, the age-adjusted rate of hypertension was 43%. Observed hypertension rates increased across age groups from 23% for ages 25-34, to 53% for ages 35-44, to 62% for ages 45-54. Definite hypertension was present in 28%. Mean systolic and diastolic blood pressure increased with age among senior staff,

714

BUNKERETAL. TABLE2 HYPERTENSION IN CIVIL SERVANTS, BENIN CITY, NIGERIA, 1987-1988 Females

Males

Hypertension”

Hypertension” Borderline

Definite

Total

Borderline

Definite

Total

n Percentage n Percentage n Percentage n n Percentage n Percentage n Percentage

Age group

n

25-34 35-44 45-54 Total Age-adjusted

158 178 102 438 rate

12 33 21 72

7 19 26 16

20 32 26 78

13 18 26 18

25-34 35-44 45-54 Total Age-adjusted

222 76 18 14 22 172 42 rate

9 24 30 24

3 22 24 49

14 29 32 28

25-34 35-44 45-54 Total Age-adjusted

136 18 102 14 284 266 36 rate

13 13 14 13

9 11 2:

7 11 11 9

32 65 53 150

20 62 3 50 2 31 9 2 52 121 7 34 33 Senior staff 10 1 5 23 40 53 25 2 46 62 61 41 4 91 52 43 Junior staff 27 20 52 4 25 24 254 7 25 3 1 59 22 80 9 23

5 4 22 6

5 6 2 13

8 12 22 11

8 8 4 20

13 16 44 17 20

10 8 17 10

1 1 1 3

10 4 17 7

2 3 2 7

20 12 34 17 -b

8 16 33 11

2 1 1 4

4 4 33 5

6 5 2 13

12 20 66 16 -b

a Borderline hypertension, SBP 2 140 and i 160 mm Hg or DBP 3 90 and < 95 mm Hg; definite hypertension, SBP a 160 mm Hg, DBP z 95 mm Hg, or on blood pressure medication; total hypetension, definite plus borderline hypertension. b Not calculated due to small numbers.

but not among junior staff (Table 1). A similar pattern was observed between BMI and age and staff level, with no increase in BMI among junior staff, 21.5,22.3, and 20.9 across age groups 25-34, 35-44, 45-54, respectively, while BMI increased with age among senior staff, 22.6, 23.8, and 25.7, respectively (Table 1). The occurrence of hypertension increased by sex-specific tertile of BMI among senior and junior staff, but within each tertile, occurrence was approximately twofold higher among senior staff than among junior staff (Table 3). When categorized by age group and BMI tertile, the percentage hypertension was up to three times higher among senior staff in every age-tertile group except for the third tertile of BMI, ages 25-34 (Fig. 1). The occurrence of hypertension in males was positively related to education; 26% of those completing primary school were hypertensive, 34% of those completing secondary school, and 45% of those who had attended a university. Staff status was related to education, as would be expected. However, as demonstrated in Table 3, at each education level the percentage of the senior staff with hypertension was higher than that of the junior staff. Occurrence of hypertension was higher among male alcohol drinkers than among abstainers for both senior and junior staff (Table 3). About 10% more junior staff than senior staff in each age group reported drinking (data not shown). Among drinkers, staff levels did not differ in drinks per week (4.9 and 4.4 drinks per week, senior and junior staff, respectively). Among women, staff level was not related to blood pressure or BMI (Table l), to prevalence of hypertension (Table 2), or to alcohol drinking (data not shown). Male senior staff had lived more years in an urban setting than junior staff in the

HYPERTENSION

715

IN NIGERIANS

TABLE 3 PERCENTAGE OF MALE SENIOR AND JUNIOR STAFF CIVIL SERVANTS, BENIN CITY, NIGERIA, 1987-1988 WITH HYPERTENSION, BY AGE GROUP, BMI TERTILE, EDUCATION LEVEL, AND ALCOHOL-DRINKING STATUS

Senior staff n in BMI tertiles Low (13.4-20.7) Med (20.8-23.7) High (23.842.2) Education level‘ None Primary Secondary Univitech AlcohoF’ Drinker Abstainer

Junior staff

P

group

n Htn”

Percentage Htn

n in group

n Htnb

Percentage Htn

valueb

32 52 88

13 24 54

41 46 61

107 103 56

14 24 21

13 23 38

0.0006 0.004 0.005

1 18 61 90

0 12 36 43

67 59 48

1 115 130 19

1 22 29 6

19 22 32

0.00002 0.00000 0.20

103 69

60 31

58 45

181 84

48 11

27 13

0.00000 0.00001

LIHypertension, SBP 2 140 mm Hg, DBP 2 90 mm Hg, or on blood pressure medication. b P value for x2 comparing senior and junior staff. c Education level was missing for two senior staff and one junior staff. d Alcohol intake status was missing for one junior staff.

two younger age groups, ages 25-34, 21.9 vs 16.6 years; ages 35-44, 26.0 vs 23.0 years; but not at ages 45-54,34.1 vs 33.7 years (ANOVA, P = 0.004 for staff level across all age groups). Only 12% (26/212) ofjunior staff and 12% (18/148) of senior staff had never lived in a rural area. Fifty-five percent of junior staff and 54% of Percent

Hypertension

80 - ~_....

_

*BMI (kg/m*) 1, 13.4-20.7; 3. 23.8-42.2.

n=18

terttles: 2, 20.8-23.7;

60

n-34

I

n.16

n=47

r

n-4,

I

I

11.24

(25-34)

(35-44)

I ,,‘,’ _j ,’

(45-54)

Age Groups m Junior m Senior FIG. 1. Hypertension by age, staff level, and tertile of body mass index in 438 male civil servants,

Benin City, Nigeria, 1987-1988.

716

BUNKER ET AL.

senior staff had lived in the rural setting for at least 15 years. Neither years of urban living nor years of rural living were correlated with blood pressure after adjustment for age. Occurrence of hypertension did not differ significantly by tribal origin (Ibo, 28/81, 35%; Edo, 87/273, 32%; or Benin River Delta region tribes, 32/72, 44%), sickle cell status (30), or glucose-6-phosphate dehydrogenase deficiency status (30). There was no difference in the occurrence of hypertension across ministries (data not shown). Only seven subjects had proteinuria (+ or + + by Multistix, 230-100 mg protein/liter urine). Six of these were hypertensive. Microalbuminuria (>30 mg/ liter urine albumin by Albusure test and negative or trace by Multistix) was present in 20% (211104) of subjects with hypertension and 8% (21/247) of normotensive subjects. Fasting blood glucose levels were slightly higher in females than in males (82.4 vs 77.6 mg/dl, P = 0.02). Male senior staff did differ significantly from junior staff in fasting glucose (80.3 vs 76.2 mg/dl). Fasting glucose was not significantly COTrelated with blood pressure, BMI, or age in males or females. Three males had fasting glucose levels of 140 mg/dl or higher. Two of these were hypertensive senior staff and one was normotensive junior staff. The two senior staff were the only subjects with glycosuria. In logistic regression analyses, senior staff, BMI, alcohol drinking, and age were all positively and independently related to hypertension in males (Table 4), while education was not significantly related (P value to enter logistic equation, 0.47). None of the interaction terms of BMI, age, and staff status were significant. Among females, only BMI was independently related to hypertension. DISCUSSION

The population studied was not representative of the general Nigerian population, the majority of whom remain in a more rural setting and are predominantly self-employed in farming or other activities. Instead, it represents an important TABLE 4 LOGISTIC REGRESSION FOR FACTORS RELATED TO HYPERTENSION IN NIGERIAN CIVIL SERVANTS

Males Factor Senior staff BMI Tertile 2” Tertile 3b Alcohol drinker Age (interval variable, 10 year age groups)

Females

Odds ratio

95% Confidence interval

2.62

1.61-4.29

1.40

1.70 2.88 1.85

0.97-2.99 1.64-5.08 1.15-2.98

5.31 13.20 0.41

1.42

1.03-1.96

1.82

u Tertile 2: Males, 20.8-23.7; females, 22.6-26.2. b Tertile 3: Males, 23.8-42.2; females, 26.3-36.4.

Odds ratio

95% Confidence interval 0.39-4.99 0.56-50.0 1.54-113.0 0.14-1.25 0.72-4.57

HYPERTENSION

717

IN NIGERIANS

population in transition from a rural to an urban, higher income and education environment, and it is a population somewhat comparable to blacks in Westernized settings. The population is of interest because of the apparent high risk for hypertension among males. Hypertension rates among males in this working population were similar to age-specific rates among U.S. blacks, 19761980 (10) (Table 5). This similarity argues against the major premise for the hypothesis of strong genetic selection for hypertension-related factors aboard slave ships (11). The premise that blood pressure or prevalence of hypertension in African populations has been lower than that in U.S. black populations appears to be true across the broad range of sub-Saharan African population studies (31). However, inclusion of populations that are little involved in the ancestry of U.S. blacks seems inappropriate, particularly the East Africans who have been found, by meta-analysis, to have significantly lower systolic blood pressure than West African blacks (31). In a more relevant comparison, systolic blood pressure in 40- to 49-year-old urban West Africans was the same as that in U.S. urban blacks, as found by metaanalysis (134.8 vs 134.4 mm Hg, respectively) (31). This, along with the high rates of hypertension in the current study and similar high rates in other Nigerian studies (16-19), suggests that the risk for hypertension is not lower among West Africans and could even become higher as development continues. While there may have been some genetic selection for salt conservation aboard slave ships (1 1), one can postulate other types of selection that could have been very important to survival, e.g., immune system capabilities or the ability to procure necessities in a time of scarcity. On the other hand, along the same vein as the slave ship hypothesis, one could theorize that West African blacks have undergone longterm selection for salt conservation as a result of high mortality from childhood diarrhea (32). In the absence of evidence that U.S. blacks differ from African blacks in salt metabolism, and in the presence of evidence that both U.S. blacks and West African blacks have a high risk for hypertension, the slave ship hypothesis, provocative though it is, is left with little support. The very low rates of proteinuria, glycosuria, and diabetes in this study suggested that the majority of hypertensive subjects had essential hypertension. In 1967-1968, Akinkugbe (16) found a high rate of proteinuria in Western Nigerian urban (10%) and rural (36%) subjects by dipstick. Proteinuria was unrelated to TABLE 5 HYPERTENSION IN MALE NIGERIAN CIVIL SERVANTS AND U.S. BLACKS

Percentage hypertensive” Age (years)

Nigerian civil servants

U.S. black@

25-34 354 45-54

20 37 52

23 42 52

a Systolic blood pressure 2140, diastolic blood pressure 390, or taking antihypertensive medication. b NHANES II, 1976-1980 (10).

718

BUNKER

ET AL.

hypertension. He suggested that the proteinuria was due to urinary schistosomiasis, which was endemic in Western Nigeria, or to gonococcal urethral stricture. In the current population, proteinuria was rare (2%) and was related to hypertension. However, microalbuminuria was not rare; it was present in 20% of the hypertensives and 8% of the normotensives. While some of the microalbuminuria is probably blood pressure related, the remainder is due to unidentified factors. Among females, hypertension rates appeared to be low, but the sample was small and younger than the males, reflecting the more recent entry of women into the work force. BMI was very strongly related to blood pressure among women, r = 0.44, compared with such correlations observed among men, r = 0.33, or among USblack women, Y = 0.20-O-30 (reviewed in (33)). Alteration of blood pressure by treatment may lower the observed correlations among the U.S. blacks. Among the Nigerian blacks, the rarity of treatment for hypertension (5% of women and 9% of men) resulted in only minimal alteration of the blood pressure distribution, and high correlations between blood pressure and BMI were observed. However, even though BMI for women was higher than that for men and was strongly correlated with blood pressure among Nigerian women, the occurrence of hypertension among women was considerably lower than that among men. A similar, but even larger disparity in blood pressure between females (110.6/69.8 mm Hg) and males (124.7/80.4 mm Hg) was seen in an earlier study of medical students (mean age, 20.4 years) in Benin City (34). Blood pressure among the 49 male students was similar to that among 25 to 34-year-old male civil servants, while BMI was somewhat lower (20.1 vs 21.6). Blood pressure among the 16 female students (110.6/69.8 mm Hg) was considerably lower than that among 25 to 34-year-old female civil servants (114.2/74.8 mm Hg), as was BMI (20.7 vs 24.1). The BMI difference suggests primarily adult weight gain among Nigerian women, as is the usual pattern among U.S. black women (reviewed in (33)), but this requires confirmation and further study. Although 37% of civil servant females reported drinking alcohol, drinking was light (among drinkers, 1.6 drinks/week compared with 4.6 drinks/week for men), and no relationship to hypertension was observed. We hypothesize that a female’s social status is determined primarily by the status of her parents or husband, rather than by her own job status, and that this explains the lack of relationship between staff status and occurrence of hypertension among females. The high rates of hypertension among males were due mainly to the striking increase with age among the senior staff, while among junior staff, occurrence was low and did not rise across age groups. BMI was strongly related to hypertension even among the junior staff. However, Fig. 1 shows much higher rates of hypertension among senior staff, after controlling for BMI and age. Alcohol was also related to the occurrence of hypertension in this study. However, there was no significant difference in alcohol consumption between junior and senior staff, and this factor was therefore not an important determinant of the differences in occurrence between senior and junior staff. About half of both junior and senior staff reported living in a rural setting for at least 15 years, presumably migrating to the urban area after childhood, although our data did not document this. The senior

HYPERTENSION

IN NIGERIANS

719

staff had lived more years in an urban setting. However, in the oldest group, in which the largest differences in rates of hypertension were observed, no difference in urban years was observed. It appears that urbanization per se is not an important factor. Our data on other potential confounders, distribution of genetic disorders with some reported relationship to hypertension, e.g., sickle cell trait (35), glucose-6phosphate dehydrogenase deficiency (36), or general genetic background, e.g., tribal origin, did not show any relationships to the occurrence of hypertension (30). Selection may have contributed to the difference in occurrence of hypertension between male junior and senior staff. There were few older junior staff. After long years of service and increasing assumption of responsibility, some junior staff, even with little education, are promoted to senior staff, e.g., senior drivers. These persons may have higher risk for hypertension, as suggested by the high rate of hypertension among senior staff with only primary school education (Table 3). Because current staff lists of the ministries were not available, the precise population denominator could not be determined. A self-selection that could have occurred was lack of participation among older hypertensive junior staff or selection for older hypertensive senior staff. Although this cannot be ruled out, several lines of evidence suggest that this was not an important factor. The method of recruiting the entire senior and junior staffs of a specific work area each day appeared to be very effective in this extremely cooperative population, with participation estimated at 85-90%. Also, if self-selection were occurring to an important degree, it might have differed by time period or ministry. However, very similar age-specific rates of hypertension among senior and junior staff were observed in the 1987 and in the 1988 sample (data not shown). Also, the rates of hypertension among senior and junior staff were very similar across the six ministries (data not shown). Most importantly, since there was a very low level of diagnosis and awareness of hypertension among the subjects, this type of selfselection probably had little influence. It is interesting to consider whether the difference in occurrence of hypertension between junior and senior civil servants was due to factors related directly to occupation or whether staff status served as a marker for socioeconomic statusrelated factors. Oviasu and Okupa (37) compared the blood pressures of male rural office clerks at a palm oil plantation, of urban clerical civil servants, and of rural field laborers in Nigeria. All three groups were predominantly equivalent to junior staff. No significant differences in blood pressure were observed among the three groups. Simmons et al. (23) found no relationship of occupation or education to blood pressure between urban white collar workers and urban manual laborers, both groups living in crowded public housing in Malawi. Idahosa (19) found no significant difference in occurrence of hypertension between urban male junior civil servants and males serving in the National police force. These studies of generally lower to middle socioeconomic level subjects found no significant differences by occupation. In the present study, physical aspects of the work of junior and senior staff were similar, i.e., they were predominantly sedentary and

720

BUNKER

ET AL.

worked in the same physical environment. Job responsibility and stress certainly may have differed, but we were not able to measure this. We hypothesize that the high prevalence of hypertension among the male senior staff was related primarily to higher socioeconomic status rather than to occupational factors. This pattern is the opposite of that observed in the Second National Health and Nutrition Examination Survey in the United States, where blood pressure was higher among persons with less education (10). In that survey, the inverse relationship was not observed among U.S. black males. However, other studies of U.S. blacks have found a strong negative relationship between blood pressure or hypertension and education (38, 39) or social class (40-42). Study of the reversal of this relationship in developing countries compared with developed countries should help clarify factors that may be important in the etiology of hypertension, including differences in diet, particularly in calorie, protein, fat, sodium, and potassium intakes, exercise, migration patterns, and stress related to changes in family structure, job demands, and social status. This population, which appears to be in transition from low prevalence to high prevalence of hypertension, provides a valuable opportunity to identify factors related to this change. ACKNOWLEDGMENTS The cooperation of the civil servants in the Ministries of Bendel State, Benin City, Nigeria, is gratefully acknowledged.

REFERENCES 1. Donnison CP. Blood pressure in the African native. Lancer 1929; l&7. 2. Kaminer B, Lutz WPW. Blood pressure in Bushmen of the Kalahari Desert. Circulation 1960; 22:289-295. 3. Shaper AG, Wright DH, Kyobe J. Blood pressure and body build in three nomadic tribes of Northern Kenya. E Afr Med J 1969; 46:273-281.

4. Mann GV, Shaffer RD, Anderson RS, Sandstead HH. Cardiovascular disease in the Masai. .I Arheroscler Res 1964; 4:289-312. 5. Truswell AS, Kennelly BM, Hansen JDL, Lee RB. Blood pressure of !Kung bushmen in Northern Botswana. Am Heart J 1972; 845-12. 6. Forsyth DM. Preliminary communication. Hypertension in Tanzania. E Afr Med J 1969; 46:30% 312. 7. Williams AW. Blood pressure differences in Kikuyu and Samburu communities in Kenya. E Afr Med J 1969; 46~262-272. 8. Ree GH. Arterial pressures in a West African (Gambian) rural population. J Trop Med Hyg 1973; 16~65-70. 9. Pobee JOM, Larbi EB, Belcher DW, Wurapa FK, Dodu SRA. Blood pressure distribution in a rural Ghanaian population. Trans R Sot Trop Med Hyg 1977; 71:66-72.

10. Drizd T, Dannenberg AL, Engel A. Blood pressure levels in persons 18-74 years of age in 1976-80, and trends in blood pressure from 1960to 1980in the United States. National Center for Health Statistics. Vital and Health Statistics. Public Health Service, Washington, DC. U.S. Gov. Printing Office, July, 1986. Series 11, No. 234, DHHS Pub. No. (PHS)86-1684. 11. Wilson TW, Grin CE. Biohistory of slavery and blood pressure differences in blacks today. A hypothesis. Hypertension 1991; 17:1122-1128. 12. Abrahams DG, Alele CA, Barnard BG. The systemic blood pressure in a rural West African community. W Afr Med J 1960; 945-58.

HYPERTENSION

IN

NIGERIANS

721

13. Shaper AG, Saxton GA. Blood pressure and body build in a rural community in Uganda. E Afr MedJ 1969;46:228-245. 14. Seedat YK, Seedat MA, Nkomo MN. The prevalence of hypertension in the urban Zulu. S Afr MedJ 1978; 53~923-927. 15. Scotch N, Gampel B, Abramson JH, Slome C. Blood pressure measurements of urban Zulu adults. Am Heart J 1961; 61:173-177. 16. Akinkugbe 00, Ojo OA. Arterial pressures in rural and urban populations in Nigeria. Br Med J 1069; 2~222-224. 17. Johnson TO. Arterial blood pressures and hypertension in an urban African population sample. Br J Prev Sot Med 1971; 25:26-33. 18. Oviasu VO, Okupa FE. Arterial blood pressure and hypertension in Benin in the equatorial forest zone of Nigeria. Trop Geogr Med 1980; 32:241-244. 19. Idahosa PE. Hypertension: An ongoing health hazard in Nigerian workers. Am JEpidemioll987; 125:85-91 20. Sever PS, Gordon D, Peart WS, Beighton P. Blood-pressure and its correlates in urban and tribal Africa. Lancer, 1980; 2:60-64. 21. M’Buyamba-Kabangu JR, Fagard R, Lijnen P, Mbuy wa Mbuy R, Staessen J, Amery A. Blood pressure and urinary cations in urban Bantu of Zaire. Am J Epidemiol 1986: 124957-968. 22. Shaper AG, Leonard PJ, Jones KW, Jones M. Environmental effects on the body build. blood pressure and blood chemistry of nomadic warriors serving in the army in Kenya. E Afr Med J 1969; 46:282-923. 23. Simmons D, Barbour G, Congleton J, Levy J, Meacher P, Saul H, Sowerby T. Blood pressure and salt intake in Malawi: An urban rural study. J Epidemiol Community Health 1986; 40:188-192. 24. Sever PS, Poulter NR. A hypothesis for the pathogenesis of essential hypertension: The initiating factors. J Hypertension 1989; 7(Suppl. l):S9-S12. 25. Reed TE. Caucasian genes in American Negroes. Science 1969; 165:762-768. 26. Dischinger P, DuChene AG. Quality control aspects of blood pressure measurements in the Multiple Risk Factor Intervention Trial. Controlled C/in Trials 1986; 7:137S-157s. 27. Coonrod BA, Ellis D, Becker DJ, Dorman JS, Drash AL, Kuller LH, Orchard TJ. Assessment of Albusure and its usefulness in identifying IDDM subjects at increased risk for developing clinical diabetic nephropathy. Diabetes Care 1989; 12:389-393. 28. Norusis, MJ. SPSS/PC+ for the IBM PC/XT/AT. Chicago, IL: SPSS, Inc., 1986. 29. BMDP Statistical Software, Inc., Los Angeles, CA, 1990. 30. Nwankwo MU, Bunker CH, Ukoli FA, Omene JA, Freeman DT, Vergis EN, Yeh LL, Kuller LH. Blood pressure and other cardiovascular disease risk factors in black adults with sickle cell trait or glucose-6-phosphate dehydrogenase deficiency. Genet Epidemiol 1990; 7:21I-218. 31. Wilson TW, Hollifield LR, Grim CE. Systolic blood pressure levels in black populations in Sub-Sahara Africa, the West Indies, and the United States: A meta-analysis. Hypertension 1991; 18:1-87-I-91.

32. Snyder JD, Merson MH. The magnitude of the global problem of acute diarrhoeal disease: A review of active surveillance data. Bull WHO 1982; 6tk605413.33. 33. Kumanyika S, Adams-Campbell LL. Obesity, diet, and psychosocial factors contributing to cardiovascular disease in blacks. In: Elijah Saunders, M.D., Ed. Cardiovascular Diseases in Blacks. Philadelphia, PA: Davis, 1991. 34. Adams-Campbell LL, Nwankwo MU, Omene JA, Ukoli FA, Young MP, Haile GT, Kuller LH. Assessment of cardiovascular risk factors in Nigerian students. Arteriosclerosis 1988; 8:793796. 35. Reid HL, Anah CO. Haemorheological parameters in hypertensive Nigerians with and without sickle-cell trait. Angiology 1985; 36:37%386. 36. Weisenfeld SL, Petrakis NL, Sams BJ, Collen MF, Cutler JL. Elevated blood pressure, pulse rate and serum creatinine in Negro males deficient in glucose-6-phosphate dehydrogenase. N Engl JMed 1970; 282:1001-1002. 37. Oviasu VO, Okupa FE. Relation between hypertension and occupational factors in rural and urban Africans. Bull WHO 1980; 58:485-489.

122

BUNKER

ET AL.

38. Dyer AR, Stamler J, Shekelle RB, Schoenberger J. The relationship of education to blood pressure. Findings on 40,000 employed Chicagoans. Circulation 1976; 54~987-992. 39. Keil JE, Sandifer SH, Loadholt CB, Boyle E. Skin color and education effects on blood pressure. Am J Public Health 1981; 71532-534. 40. Syme SL, Oakes TW, Friedman GD, Feldman R, Siegelaub AB, Collen M. Social class and racial differences in blood pressure. Am J Public Health 1974; 64~619-620. 41. Keil JE, Tyroler HA, Sandifer SH, Boyle E. Hypertension: Effects of social class and racial admixture. The results of a cohort study in the black population of Charleston, South Carolina. Am J Public Health 1977; 67r634-639. 42. Howard J, Holman BL. The effects of race and occupation on hypertension mortality. Milbank Mem Fund Q 1970; 48:263-296. Received December 3, 1991 Revised May 15, 1992 Accepted May 15, 1992