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Ascherio G, Hennekens C, Willet WC, Sacks F, Rosner B, Manson J, Witteman J, Stampfer MJ

Prospective study of nutritional factors, blood pressure, and hypertension among US women

Hypertension (May) 27:1065-1072 1996

Lifestyle modification is central to the management of hypertension. Excessive alcohol consumption and obesity are known to elevate blood pressure. Debate rages over the roles of salt and calcium intake. Ascherio et al report the results of their analysis of diet and blood pressure data from The Nurses' Health Study.

Methods: A prospective cohort study, this study provided four-year follow-up data for 41,541 normotensive, mostly white (98%) women without diabetes or evidence of hypertensive vascular disease. Data was obtained by questionnaire, but was corroborated by substudy evaluation for accuracy. A new diagnosis of hypertension and absolute blood pressure in non-hypertensive women were the outcomes of interest. The primary dietary factors evaluated were calcium, magnesium, potassium and fiber.

Results: Age, body mass index and alcohol consumption are clinically significant risk factors for the development of hypertension. Sodium, calcium, potassium, magnesium and fiber intake are not. Among normotensive women, however, magnesium and fiber intake are statistically significant predictors of both systolic and diastolic BP. Women consuming more than 350mg of magnesium daily had systolic pressures 1.3 mmHg and diastolic pressures 1.0 mmHg lower than those whose intake was less than 200mg. Women consuming greater than 25 g/d of fiber had systolic pressures 1.1 mmHg and diastolic pressures 1.1 mmHg lower than women eating less than 10 g/d. Some attempt was made to characterized the types of food which provide the best source of these nutrients. Not surprisingly, fruits and vegetables were generally beneficial, while red meat, potatoes and sweets were not. Eggplant was a surprising loser, being associated with a small increase in systolic pressure.

Conclusions: Magnesium and fiber may reduce BP levels. Diets rich in fruit, vegetables, dark bread and chicken may reduce BP.

Comment: This is a large, rigorously conducted and carefully verified observational study. It confirms the accepted increase in risk for hypertension attributable to age, obesity and alcohol intake. Low sodium intake (2.8g/day in the highest quintile) in these low-risk (white) women effectively invalidates any conclusions regarding the association between salt and hypertension. Confounding by the effects of treatment likely prevented the authors from evaluating the relationship between dietary factors and absolute blood pressure in hypertensive women. Self-reported blood pressures are imprecise, at best. While statistically significant, the effects of magnesium and fiber on blood pressure in normotensive women is clinically negligible. (John E. Antonsen, MD, UW Nephrology Clinical Research Training Group, Seattle WA)