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
(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
(John E. Antonsen, MD, UW Nephrology Clinical Research Training
Group, Seattle WA)