Angiotensinogen levels and obesity in four black populations. ICSHIB Investigations

BACKGROUND: The relationship between circulating levels of angiotensinogen and hypertension in the epidemiologic setting has not been studied much. Recent findings related to the association between hypertension and polymorphisms of the angiotensinogen gene have generated new interest in this potential pathway to hypertension. OBJECTIVES: To examine environmental factors associated with levels of circulating angiotensinogen as determinants of hypertension in populations of African origin. METHODS: We recruited 1557 participants from communities in Nigeria (n = 611), Zimbabwe (n = 161), Jamaica (n = 476), and Maywood, Illinois, USA (n = 309). RESULTS: Mean angiotensinogen levels varied widely across groups (Nigeria 1381 ng/ml angiotensin I generated, Zimbabwe 1638 ng/ml angiotensin and I generated Jamaica 1801 ng/ml angiotensin I generated, and Maywood 2039 ng/ml angiotensin I generated). Average body mass index was highly correlated to angiotensinogen level across the population samples, accounting for 90 percent of the between-sample variation. At the individual level the correlation between body mass index and angiotensinogen level was substantially smaller, in the range 0.04-0.15, although the association attained statistical significance for all but one of the populations. Women had higher levels of angiotensinogen and mean levels in subjects of both sexes declined in late middle age. Hypertensives also had significantly higher levels of angiotensinogen and we noted correlations to blood pressure for two of the four populations. CONCLUSIONS: Obesity, sex and age would all appear to be important modifiers of circulating angiotensinogen levels. The variation in level across populations was substantially larger than that which has been found previously in association with known genetic polymorphisms within populations, suggesting the possibility that environmental effects are more important than had previously been recognised.(AU)

Leptin and body composition of Nigerians, Jamaicans, and US blacks

The role of leptin in humans remains controversial. Leptin concentrations are highly correlated with body fat stores. We tested whether or not this relation was consistent across the range of body composition encompassing the lean as well as the obese. Individuals participating in community-based comparative research in Nigeria (n = 363), Jamaica (n = 372), and the United States (Maywood, IL; n = 699) had their plasma leptin concentrations and body compositions (with bioelectrical impedance analysis) measured. All participants identified themselves as being black. Body mass index (in KG/m2) ranged from across populations for both men and women in Nigeria, Jamaica, and the United States, respectively (men: 2.8, 3.9, and 6.8 microg/L; women: 10.3, 18.6, and 27.7 microg/L). An exponential function fit the relation between percentage body fat or total fat mass and leptin for men and women at each site. For women and men the exponential function with either percentage body fat or total fat mass was of the same shape, but increased by a constant in women, yielding higher leptin concentrations than in men at every level of body fat. On the basis of this broad distribution of body composition, the data suggest an exponential response of leptin to increase in body fat stores, consistent with the development of leptin resistance in individuals developing obesity. These findings likewise confirm that men and women exhibit different set points in terms of leptin production(AU)

Relation between body mass index and body fat in black population samples from Nigeria, Jamaica, and the United States

Body mass index (BMI) is the most commonly used measure of obesity. Recently, some investigators have advocated direct measurement of adiposity rather than use of the BMI. This study was undertaken to determine the ability of BMI to predict body fat levels in three populations of West Africa heritage living in different environments. A total of 1,054 black men and women were examined in Nigeria, Jamaica, and the United States during 1994 and 1995. A standardized protocol was used to measure height, weight, waist and hip circumferences, and blood pressure at all sites; percentage of body fat was estimated using bioelectrical impedance analysis. Percentage of body fat and BMI were highly correlated within site- and sex-specific groups, and the resulting r2 ranged from 0.61 to 0.85. The relation was quadratic in all groups except Nigerian men, in whom it was linear. The regression coefficients were similar across sites, yet the mean body fat levels differed significantly (p < 0.001) as estimated by the intercept, making intersite comparison difficult. Compared with BMI, percentage of body fat was not a better predictor of blood pressure or waist or hip circumference.(AU)

Polymorphisms of renin-angiotensin genes among Nigerians, Jamaicans, and African Americans

Within the context of an international collaborative study of the evolution of hypertension in the black disapora, we determined the allelic distribution of hypertension candidate genes for the renin-angiotensin system in three populations of African origin. The insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE) and the M235T and T174M variants of the angiotensinogen (AGT) gene were examined in individuals from Nigeria, Jamaica, and the United States. Large differences in the prevalence of hypertension were recorded in door-to-door surveys, ranging from 16 percent in Nigeria to 33 percent in the United States. The frequency of the D allele was similar in all groups (54 percent, 59 percent and 63 percent in Nigeria, Jamaica, and the United States, respectively). The 235T allele of the AGT gene was found in 81 percent of US and Jamaican blacks and 91 percent of Nigerians: very little variation was seen for the T174M marker. Despite larger differences in hypertension rates, genetic variation at the index loci among these groups was modest. Overall, the frequency of the ACE D allele was only slightly higher than that reported for European and Japanese populations, whereas the AGT 235T allele was twice as common. Compared with blacks in the western hemisphere. Nigerians had a higher frequency of the 235T allele, which is consistent with 25 percent European admixture in Jamaica and the United States. The results indicate the potential for etiolgic heterogeneity in genetic factors related to hypertension across the ethnic groups while suggested that environmental exposures most likely explain the gradient in risk in the comparison among black populations.(AU)