Patterns of sodium and potassium excretion and blood pressure in the African Diaspora.

Habitual levels of dietary sodium and potassium are correlated with age-related increases in blood pressure (BP) and likely have a role in this phenomenon. Although extensive published evidence exists from randomized trials, relatively few large-scale community surveys with multiple 24-h urine collections have been reported. We obtained three 24-h samples from 2704 individuals from Nigeria, Jamaica and the United States to evaluate patterns of intake and within-person relationships with BP. The average (±s.d.) age and weight of the participants across all the three sites were 39.9±8.6 years and 76.1±21.2 kg, respectively, and 55% of the total participants were females. Sodium excretion increased across the East-West gradient (for example, 123.9±54.6, 134.1±48.8, 176.6±71.0 (±s.d.) mmol, Nigeria, Jamaica and US, respectively), whereas potassium was essentially unchanged (for example, 46.3±22.9, 40.7±16.1, 44.7±16.4 (±s.d.) mmol, respectively). In multivariate analyses both sodium (positively) and potassium (negatively) were strongly correlated with BP (P<0.001); quantitatively the association was stronger, and more consistent in each site individually, for potassium. The within-population day-to-day variation was also greater for sodium than for potassium. Among each population group, a significant correlation was observed between sodium and urine volume, supporting the prior finding of sodium as a determinant of fluid intake in free-living individuals. These data confirm the consistency with the possible role of dietary electrolytes as hypertension risk factors, reinforcing the relevance of potassium in these populations.

Relationship between blood pressure and physical activity assessed with stable isotopes.

Intrapopulation and interpopulation variation in blood pressure (BP) often reflects the joint effect of a complex set of risk factors, including lifestyle factors such as physical activity, diet, smoking and alcohol use. In this study, we set out to quantify the impact of habitual levels of physical activity on BP within and between three populations at contrasting levels of population risk of hypertension. Individuals were randomly sampled from communities in Nigeria (n=57), Jamaica (from Kingston, n=35) and the United States (from the Chicago area, n=32). Activity energy expenditure (AEE) (estimated from resting energy expenditure measured by indirect calorimetry and total expenditure measured with doubly labelled water) was used as an objective estimate of physical activity. In each of the three samples, there was a consistent negative correlation between BP and AEE. This negative association persisted after adjustment for age, sex and body fat (body mass index or percent fat mass). In multivariate models, adiposity was no longer a significant predictor of BP after accounting for low AEE. In conclusion these data suggest that habitual levels of physical activity may have a generalizable relationship with BP in populations with widely different social and environmental characteristics.

A randomized trial on sodium reduction in two developing countries.

Hypertension remains the most common cardiovascular risk factor in developing countries, yet the majority of patients have no access to pharmacological therapy. Population-wide preventive strategies, such as salt restriction, are an attractive alternative, but experience in resource-poor settings is limited. To address this question, we conducted a randomized crossover study of salt restriction in adults living in Nigeria and Jamaica in order to estimate the mean blood pressure (BP) response. After a 4-week run-in period to determine willingness to adhere to a low-salt diet, 56 Jamaicans and 58 Nigerians completed an 8-week crossover study of low-salt and high-salt intake. Baseline BPs were in the normotensive range (systolic=125 mmHg in Jamaica, 114 mmHg in Nigeria). Baseline urinary sodium excretion was 86.8 and 125.6 mEq/day in Nigeria and Jamaica, respectively. The mean difference between urinary sodium excretion at baseline and at the end of the 3-week low-sodium phase was 33.6 mEq/day in Nigeria and 57.5 mEq/day in Jamaica. During the high-sodium phase, mean change in urinary sodium excretion from baseline to week 3 was 35.0 and 5.5 mEq/day in Nigeria and Jamaica, respectively. The mean change in systolic BP ('high' vs 'low' sodium phase) was approximately 5 mmHg in both groups. This study suggests that the efficacy of sodium reduction in developing countries equals those noted in more affluent cultures. If promoted on a wide scale, sodium reduction could be used to treat persons with established hypertension, and more importantly, to prevent age-related increases in BP in poor communities.

Energetic determinants of glucose tolerance status in Jamaican adults.

As type 2 diabetes mellitus (DM2), obesity and sedentary lifestyles are increasing in developing countries, this observational study investigated the role of physical activity on DM2 in Jamaica. Anthropometry, body composition (by bioelectrical impedance analysis) and glucose tolerance status was assessed in 722 adults in 1993 and 1997. Energy expenditure was estimated in a subset using measured resting energy expenditure in combination with self-reported activity recalls. The rates of impaired glucose tolerance (IGT) were 23.7 and 27.3%, and DM2 were 16.3 and 23.7% among men and women, respectively. After adjusting for body composition, a one-unit increase in physical activity significantly reduced the odds of having diabetes (OR = 0.05; 95% CI: 0.004, 0.66), but not IGT. Hence, decreased physical activity is a significant independent contributor to the high rates of glucose intolerance in Jamaica. Efforts must be directed at minimizing obesity and increasing physical activity in developing countries.

Heritability of obesity-related traits among Nigerians, Jamaicans and US black people.

OBJECTIVE: The mean values for anthropometric traits vary across population groups and this variation is clearly determined for the most part by the environment. The familiarity of anthropometric traits also varies in reports from different populations, although this variation has not been shown to follow a consistent pattern. To examine whether heritability is influenced by socio-cultural factors, we conducted a cross-cultural study of populations of the African diaspora. PARTICIPANTS: Data were collected on 1868 family members from Nigeria, 623 from Jamaica and 2132 from metropolitan Chicago, IL, USA. MEASUREMENTS: Height and weight were measured and body mass index (kg/m(2)) calculated. Fat-free mass, fat mass and percentage body fat were estimated using bioelectrical impedance analysis. Plasma leptin concentrations were also measured. The proportion of variance attributable to additive genetic and non-shared environmental components was estimated with the maximum likelihood variance decomposition method. RESULTS: Mean values for all anthropometric traits increased along the socio-cultural gradient, and obesity increased from 5% in Nigeria to 23% in Jamaica and 39% in the USA. Within populations the relationships among traits both within individuals and within families were highly consistent. Heritability estimates for weight, body mass index, fat mass and percentage body fat were approximately 50% for all groups. Heritability for height was lower in Nigeria (62%) than in Jamaica (74%) or the US (87%). CONCLUSION: The familial patterns of body size and energy storage appear to be consistent in these genetically related populations across a wide range of environmental conditions.