Diet plays such an important role in hypertension that in those with a BP of 140-159/90-99 mm Hg, dietary changes alone can serve as initial treatment before starting antihypertensive medications. Moreover, among patients already on antihypertensives, dietary changes can further lower BP and facilitate medication step-down.
These findings are presented in a new scientific statement from the American Heart Association (Hypertension. 2006;47:296-308). Summarizing the best clinical research to date, the statement — written by a panel of leading medical and research authorities — is explicit about which foods, minerals, and supplements clinicians should and should not prescribe for their patients. Following is a summary of the new recommendations.
On average, as dietary sodium chloride intake rises, so does BP. In a recent meta-analysis of more than 50 randomized trials, a median reduction in urinary sodium of about 1.8 g/day lowered systolic and diastolic BP by 2.0 and 1.0 mm Hg, respectively, in nonhypertensive patients and 5.0 and 2.7 in those with hypertension. In general, the effects of sodium reduction on BP tend to be greater in blacks, middle-aged and older persons, and those with hypertension, diabetes, or chronic kidney disease. These groups tend to have a less responsive renin-angiotensin-aldosterone system.
Some salt is required. An Institute of Medicine panel has set 1.5 g/day as an adequate level. But in view of the American food supply and the resulting high levels of salt consumption — more than 75% of consumed salt comes from processed products — a reduction to 1.5 g/day is not easily achievable. Therefore, a reasonable recommended limit at present is 2.3 g/day.
High potassium intake is associated with reduced BP, based on more than 30 clinical trials. Though data from individual studies were inconsistent, three meta-analyses of these trials documented a significant inverse relationship between potassium intake and BP in patients with and without hypertension. Potassium reduced BP more in blacks than in whites; in some studies, the result in blacks is striking.
Because potassium derived from foods is accompanied by other nutrients, the preferred strategy is to consume foods rich in potassium rather than supplements. Fruits and vegetables are the best dietary sources. Foods rich in potassium include apricots, avocados, bananas, melons, kiwis, lima beans, oranges, prunes, spinach, tomatoes, and squash.
The effect of potassium on BP depends on the concurrent intake of salt and vice versa. An increased intake of potassium lowers BP more in the context of a higher salt intake, and conversely, the BP reduction from a reduced salt intake is greatest when potassium intake is low. For example, a high potassium intake blunted the BP rise in response to increased salt intake in one trial of black men.
The dearth of dose-response trials precludes a firm recommendation for a specific level of potassium intake as a means to lower BP. But it is reasonable to set the recommended level at 4.7 g/day, which corresponds to the average in clinical trials. Since excess potassium is excreted in the urine, those with kidney disease should consume <4.7 g/day. ACE inhibitors, angiotensin receptor blockers, and nonsteroidal anti-inflammatory agents can also impair potassium excretion.
Studies showed a direct, dose-dependent relationship between alcohol intake and BP, especially when consumption exceeded two drinks a day. This relationship holds regardless of age, weight, or salt intake. A recent meta-analysis of 15 trials found that self-reported reduced alcohol consumption of 16%-100% lowered BP by 3.3/2.0. However, two or fewer drinks a day may reduce the risk of coronary heart disease. Women and lightweight men should consume no more than one drink (12 oz beer, 5 oz wine, or 1.5 oz 80-proof distilled spirits) a day.
In industrialized countries, vegetarians have markedly lower BPs than nonvegetarians. Some of the lowest BPs observed in industrialized countries occur in strict vegetarians, or macrobiotics. Physical activity, low body weight, increased potassium, low alcohol intake, and other aspects of the vegetarian lifestyle might lower BP, but trial evidence indicated that these factors are not fully responsible for the low BP that vegetarians achieve. In two trials, vegetarian diets reduced systolic BP about 5 mm Hg but had equivocal effects on diastolic BP.