Department of Medical Biochemistry

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Body size and blood pressure: an analysis of Africans and the African diaspora
(Epidemiology, 2008-01) Cappuccio, F.P.; Kerry, S.M.; Adeyemo, A.; Luke, A.; Amoah, A.G.; Bovet, P.; Connor, M.D.; Forrester, T.; Gervasoni, J.P.; Kaki, G.K.; Plange-Rhule, J.; Thorogood, M.; Cooper, R.S.
BACKGROUND: Blood pressure is directly and causally associated with body mass index (BMI) in populations worldwide. However, the relationship may vary across BMI in populations of African origin. METHODS: We compared the relationship between blood pressure and BMI in populations of African origin, using 13 samples from Africa, the Caribbean, the United Kingdom and the United States. We had access to data from individual participants for age, height, weight, blood pressure, and treatment of hypertension. Analysis was restricted to 18,072 participants (age 35-64 years; 44% men). We carried out multivariate regression analysis to estimate the relationship between blood pressure and BMI by country and by sex. The use of antihypertensive treatment was taken into account by exclusion and by sensitivity analysis. RESULTS: There was a positive relationship between both systolic and diastolic blood pressure and BMI. In men the slopes for systolic blood pressure varied from 0.27 mm Hg per kg/m (95% confidence interval = -0.01 to 0.56) in the United States to 1.72 mm Hg per kg/m (95% confidence interval = 0.92 to 2.53) in Ghana (Kumasi). In women, the slopes varied from 0.08 (-0.54 to 0.72) in South Africa to 1.32 (0.98 to 1.66) in the Republic of Congo. Similar variation in trends was seen for diastolic blood pressure. The higher the BMI, the shallower the slopes [-0.10 (-0.15 to -0.06) for systolic, -0.09 (-0.12 to -0.06) for diastolic]. No differences were seen after excluding persons who were being treated for hypertension. CONCLUSIONS: Blood pressure and BMI levels vary among populations of the African diaspora. The effect of BMI on blood pressure levels diminishes as BMI increases. These results suggest a complex relationship among excess body weight, adiposity, and energy expenditure.
Race and ethnicity determine serum insulin and C-peptide concentrations and hepatic insulin extraction and insulin clearance: comparative studies of three populations of West African ancestry and white Americans
(Metabolism, 1997) Osei, K.; Schuster, D.P.; Owusu, S.K.; Amoah, A.G.
We examined the importance of ethnicity in terms of β-cell secretion and hepatic insulin extraction (HIE) and insulin clearance (IC) to peripheral insulin levels before and after stimulation in three populations of West African ancestry, namely African-Americans, Ghanaian immigrants, and native Ghanaians living in diverse environments, and white Americans. Following 10 to 12 hours of overnight fasting, each subject ingested a 75-g oral glucose load. Blood samples for determination of serum glucose, insulin, and C- peptide were obtained at baseline and after the oral glucose load at 30- minute intervals for 240 minutes. Basal HIE and IC were calculated as the molar ratios of C-peptide and insulin concentrations at basal steady state, and postprandial values as molar ratios of the incremental integrated C- peptide and insulin areas. Clinical characteristics of the patients were not significantly different among the four groups. During the fasting and postprandial state, serum glucose levels were not significantly different among the four groups. Surprisingly, the mean fasting insulin concentration was significantly greater in native Ghanaians (21.19 ± 0.93 μU/mL, P < .05) than in African-Americans (11.90 ± 1.02 μU/ML), Ghanaian immigrants (8.14 ± 0.96 μU/mL), and white Americans (7.03 ± 0.78 μU/mL). Following the oral glucose load, the mean serum peak and incremental integrated areas of insulin were significantly (P < .05) greater in native Ghanaians, African- Americans, and Ghanaian immigrants compared with white Americans. In contrast, there were no significant differences in postprandial serum insulin responses among the three groups of West African ancestry, irrespective of country of origin or residence. Despite the higher insulin concentrations in blacks of West African ancestry compared with whites, the corresponding basal and postprandial serum C-peptide levels were not significantly different among the four groups. Mean basal and postprandial HIE and IC were significantly (P < .05 to .01) reduced (25% to 52%) in the three populations of West African ancestry compared with the white Americans, but these values were not significantly different among the West African descendants. When comparing metabolic responses in obese (body mass index [BMI] > 27 kg/m2) and non-obese (BMI < 27 kg/m2) native Ghanaians, we found no significant differences in fasting insulin, C-peptide, and basal HIE or IC. Also, there were no significant relations between fasting and postprandial serum insulin, obesity indices, and HIE and IC in any of the groups. In summary, our study demonstrates that glucose-tolerant native Ghanaians, Ghanaian immigrants, and African-Americans of West African ancestry manifest hyperinsulinemia and a decreased HIE and IC compared with white Americans. We conclude that race and ethnicity may be the major determinants of the mechanism(s) of β-cell secretion, insulin action, and peripheral insulin levels and HIE or IC in humans. We speculate that the lower HIE and IC in blacks of West African descent appears to be a highly conserved metabolic trait irrespective of the country of residence.
Relationships among obesity, inflammation, and insulin resistance in african americans and west africans
(Obesity, 2010-03) Doumatey, A.P.; Lashley, K.S.; Huang, H.; Zhou, J.; Chen, G.; Amoah, A.; Agyenim-Boateng, K.; Oli, J.; Fasanmade, O.; Adebamowo, C.A.; Adeyemo, A.A.; Rotimi, C.N.
Several research studies in different populations indicate that inflammation may be the link between obesity and insulin resistance (IR). However, this relationship has not been adequately explored among African Americans, an ethnic group with disproportionately high rates of obesity and IR. In this study, we conducted a comparative study of the relationship among adiposity, inflammation, and IR in African Americans and West Africans, the ancestral source population for African Americans. The associations between obesity markers (BMI and waist-to-hip ratio (WHR)), inflammatory markers (high-sensitivity C-reactive protein (hsCRP), haptoglobin, interleukin (IL)-6, and tumor necrosis factor (TNF)-α), and IR (homeostasis model assessment of insulin resistance (HOMA IR)) were evaluated in 247 West Africans and 315 African Americans. In average, African Americans were heavier than the West Africans (by an average of 1.6 BMI units for women and 3 BMI units for men). Plasma hsCRP, haptoglobin, and IL-6 (but not TNF-α level) were higher in African Americans than in West Africans. In both populations, BMI was associated with markers of inflammation and with HOMA IR, and these associations remained significant after adjusting for sex and age. However, the pattern of associations between measured inflammatory markers and IR was different between the two groups. In West Africans, hsCRP was the only inflammatory marker associated with IR. In contrast, hsCRP, haptoglobin, and IL-6 were all associated with IR in African Americans. Interestingly, none of the associations between markers of inflammation and IR remained significant after adjusting for BMI. This finding suggests that in African Americans, the relationship between inflammatory markers and IR is mediated by adiposity.