High BP-obesity link varies among Africans: study
Excess fat may not be the only factor that increases the risk of high blood pressure (hypertension) among obese people of African descent, according to an international research team.
They found that while blood pressure increased with body weight in 13 different groups of Africans or people of African heritage living in the UK, United States, or the Caribbean, the degree to which blood pressure rose with body weight varied among the groups.
Evidence is strong that an increase in blood pressure as body mass index (BMI) rises is universal across the world’s populations, but there has been some research suggesting that the relationship might vary “in populations at the extremes of the BMI distribution,” Dr. Francesco P. Cappuccio of Warwick Medical School in Coventry, UK, and colleagues explain in the medical journal, Epidemiology.
To investigate the question among Africans, they looked at blood pressure data for a total of 18,072 people of African descent living in eight African nations, three Caribbean countries, the US and the UK.
Blood pressure rose in tandem with BMI for all the populations in the study, the researchers report. But the sharpness of the increase varied.
BMI is the ratio between height and weight, which indicates whether a person is underweight, overweight or within a normal weight range. Individuals with a BMI of 25 or greater are considered overweight and those with a BMI of 30 or greater are considered obese.
Cappuccio and colleagues found that while blood pressure rose by 0.27 millimeters of mercury (mmHg) for each BMI unit among US black men, it jumped by 1.72 for men in Ghana. Among women, the range was from 0.08 mmHg for each BMI unit in South Africans to 1.32 for the Republic of Congo. And within countries with a heavier population, on average, such as the United States, blood pressure rose less sharply as BMI increased.
Blood pressure may increase less dramatically with body weight among high-BMI populations because excess weight tends to be mostly fat, which does not burn as much energy as muscle and may therefore not increase blood pressure to the same degree, the researchers suggest. “This interpretation would alter the standard view that increasing fat mass, per se, is the cause of increased hypertension risk in obese people of African descent,” they write.
The results of this study, they conclude, “suggest a complex relationship among excess body weight, adiposity (body fatness), and energy expenditure.”
SOURCE: Epidemiology, January 2008.
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