Hypertension in African Americans

Hypertension (HTN) is high blood pressure (BP). African Americans (AAs) have the highest prevalence of HTN in the world. HTN is seen in 41 percent of adult AAs compared with 27 percent of Caucasians. It occurs at an earlier age, is more severe, and has more complications than in Caucasians. Obesity increases the BP in these patients, and weight loss significantly decreases their BP. The prevalence of obesity is 28 percent in AA men, 50 percent in AA women, 27 percent in Caucasian men, and 30 percent in Caucasian women.

Systolic blood pressure (SBP) is the pressure in arteries while the heart is beating; diastolic blood pressure (DBP) is the pressure while the heart is resting between beats. It is measured in millimeters of mercury (mmHg). HTN is defined as SBP above 140 and/or DBP above 90 (above 140/90 mmHg). No one knows what causes elevated BP in 95 percent of the patients with HTN. It is one of the biggest mysteries in medicine. Hypertension is probably caused by many mutations (abnormalities) in several genes. In addition, environmental factors, such as diet and exercise, affect BP.

HTN is a major reason why heart disease mortality is 50 percent higher, stroke is twice as common, and hypertensive kidney disease is four times as common in AAs. Scientists do not know why HTN in AAs is different from HTN in Caucasians. There are some gene mutations seen in hypertensive AAs that could explain part of this difference. Salt raises BP and causes fluid retention. The BP in AAs is more sensitive to salt in the diet than in Caucasians. The kidneys of many hypertensive AAs do not excrete salt in the urine as efficiently as the kidneys of many Caucasians. The reason for this is unclear. Furthermore, obesity is thought to exacerbate the effects of salt sensitivity in all populations. In 2000, there was no significant difference between the prevalence of overweight (body mass index [BMI] >25 kg/m2) or obesity (BMI above 30) in AA and Caucasian men. But AA women had a much higher prevalence of overweight (77.3 vs. 57 percent) and obesity (49.7 vs. 30.1 percent) than Caucasian women. There is some evidence that the arteries in many AA hypertensives are more sensitive to hormones and other chemicals in the body that cause constriction of the arteries and less sensitive to those that cause dilation of arteries.

Social factors contribute significantly to the prevalence of HTN in AAs. One in four AAs lives in poverty, compared with one in 12 Caucasian Americans. Poverty is a strong risk factor for HTN in many populations. Poverty is associated with poor nutrition, obesity, increased alcohol and tobacco use, and increased stress, all of which increase the risk of developing HTN. The diet of poor persons is often low in fruits, vegetables, and milk, which are rich in potassium and calcium. Diets high in potassium and calcium lower BP. Moderation of alcohol intake also lowers BP. Long-standing social stress may also be a significant factor in the development of HTN.

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