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Etiology

Increased intake of dietary fiber, potassium, and magnesium was associated with a decreased risk for hypertension in men

ACP J Club. 1993 May-June;118:91. doi:10.7326/ACPJC-1993-118-3-091


Source Citation

Ascherio A, Rimm EB, Giovannucci EL, et al. A prospective study of nutritional factors and hypertension among US men. Circulation. 1992 Nov;86:1475-84.


Abstract

Objective

To study the relation between nutrient intakes and hypertension.

Design

4-year cohort analytic study.

Setting

Community-based study in the United States.

Participants

30 681 predominantly white male health professionals aged 40 to 75 years, without hypertension and participating in the Health Professionals Follow-up Study. Exclusion criteria were daily caloric intake < 800 or > 4200 kilocalories; cancer; myocardial infarction; angina; diabetes; renal failure; high blood cholesterol; coronary artery surgery; or use of digoxin, nitrates, diuretics, β-blockers, calcium antagonists, or other antihypertensive medication.

Assessment of risk factors

Nutrient intakes (total energy, calcium, magnesium, potassium, fiber, total saturated and polyunsaturated fat, transunsaturated fatty acids, sodium, and alcohol) were calculated based on the response to a validated food-frequency questionnaire completed in 1986.

Main outcome measures

Blood pressure and diagnosis of hypertension in 1990 determined by self-report on the follow-up questionnaires.

Main results

During the 4-year follow-up period, hypertension was diagnosed in 1248 participants. Patients were divided into quintiles based on energy-adjusted nutrient intake. The lowest and highest quintiles of intake for magnesium, potassium, and dietary fiber were < 0.25 and ≥ 0.40 g/d, < 2.4 and ≥ 3.6 g/d, and < 12.0 and ≥ 24.0 g/d, respectively. After adjusting for age, relative weight, and alcohol consumption and leaving the relative risk (RR) for hypertension for the highest nutrient intake at 1.0, there was an inverse association for intakes of magnesium (RR for lowest intake level 1.49, 95% CI 1.15 to 1.92), potassium (RR 1.54, CI 1.19 to 1.96), and dietary fiber (RR 1.57, CI 1.20 to 2.05). These inverse associations were stronger in men < 50 years old. When magnesium, potassium, and dietary fiber were considered simultaneously only dietary fiber remained independently associated with the risk for hypertension. Greater fiber intake was associated with a slower rise of systolic blood pressure in all participants, hypertensive or not. Calcium was inversely associated with hypertension in men with low relative weight (Quetelet index < 23). No statistical associations with hypertension were found for total, saturated, or polyunsaturated fat; transunsaturated fatty acids; or sodium.

Conclusion

In this cohort of men, it appeared that an increased intake of dietary fiber, potassium, and magnesium was associated with a decreased risk for development of hypertension.

Source of funding: Not stated.

For article reprint: Dr. A. Ascherio, Department of Epidemiology, 677 Huntington Avenue, Boston, MA 02115, USA. FAX 617-432-2435.


Commentary

People who follow vegetarian diets, which are generally higher in fiber than nonvegetarian diets, have lower blood pressures (1). The population followed by Ascherio and colleagues was healthy and well educated, but had a wide range of fiber intake with the lowest 2 quintiles consuming less than the 17-gram average fiber intake for men shown in a previous study (2). Was it the low-fiber intake that promoted the development of hypertension?

The study participants who consumed a smaller amount of fiber were possibly not as well informed about health issues as the remainder of the cohort. They may have eaten a little less potassium and a little more sodium so that the singular effects of these behaviors were not detectable using the recall methods at hand, but in the aggregate led to higher blood pressure.

The authors' findings should encourage the internist to estimate fiber intake in all patients. The incidence of cardiovascular disease is a continuous expression of blood pressure, not just blood pressure high enough to be called "hypertension." In this cohort, higher fiber intake was associated with smaller rises in any baseline systolic blood pressure over time.

It is easy to advise a person how to increase their fiber intake. Enhancement of fiber intake could begin with a breakfast that alone provides the 12 grams of fiber observed for the lowest quintile of intake in the study: 3.5 oz of rolled oats cooked into cereal and one half grapefruit. Given the other apparent salutary effects of dietary soluble fiber, it is reasonable to correct deficient consumption to reduce risk factors for cardiovascular disease.

Michael Gutkin, MD
St. Barnabas Medical CenterLivingston, New Jersey, USA


References

1. Appel LJ, Moore TJ, Obarzanek E, et al., for the DASH Collaborative Research Group. A clinical trial of the effects of dietary patterns on blood pressure. N Engl J Med. 1997;336:1117-24.

2. U.S. Department of Agriculture. Nationwide food consumption survey. Continuing survey of food intakes by individuals: men 19 to 50 years, 1 day 1985. Hyattsville, Maryland: Human Nutrition Information Service: 1986. NFCS, CSFII report no. 85-3.