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Which nutrients reduce the risk of stroke?

 

The first study investigates the hypothesis that a high potassium intake reduces the risk of stroke. It also examines the association between risk of stroke and intake of other nutrients found in potassium-rich foods. It investigates these associations in men. The second study examines the intake of potassium and other nutrients on risk of stroke in women.

Bottom line

A high potassium intake is associated with a reduced risk of ischaemic stroke. The best way to increase dietary potassium is to eat more fruit and vegetables.

References

  1. A Ascherio et al. Intake of potassium, magnesium, calcium, and fiber and risk of stroke among US men. Circulation 1998 98: 1198-1204.

  2. H Iso et al. Prospective study of calcium, potassium, and magnesium intake and risk of stroke in women. Stroke 1999 30: 1772-1779.

Study 1

Participants were 43,738 men, aged 40 to 75 years old, from the 1986 US Health Professionals Follow-up Study. Excluded were those with a prior diagnosis of myocardial infarction, angina, coronary artery surgery, stroke, transient ischaemic attack, peripheral arterial disease or diabetes.

Information was collected on participants’ medical history, lifestyle and whether or not they had physician-diagnosed hypertension. This information was updated every two years. Diet was assessed with a 131-item food-frequency questionnaire, which asked about average frequency of intake during the previous year, use of vitamin and mineral supplements and use of potassium and magnesium supplements specifically. Participants’ nutrient intakes were divided into quintiles. Fatal and non-fatal strokes were confirmed by various means, e.g. medical records and autopsy reports.

Participants were followed for stroke incidence for eight years. A total of 328 cases were confirmed (210 ischaemic, 70 haemorrhagic and 48 unspecified).

Results

Men in the highest quintile of potassium intake (median intake 4.3 g/d) were less likely to smoke, were more physically active and consumed less alcohol, less fat, more protein and more micronutrients than men in the lowest quintile (median intake 2.4 g/d).

Results were adjusted for age, total energy intake, smoking, alcohol consumption, history of hypertension, history of hypercholesterolemia, parental history of myocardial infarction before 65 years, profession, body mass index and physical activity.

Figure 1: Relative risk of stroke (age-adjusted) in quintiles of potassium intake. Daily potassium intake (g/day) in yellow
  • Men in the highest quintile of potassium intake had a 38% reduced risk of total stroke compared with those in the lowest quintile (relative risk 0.62, 95% confidence interval 0.43 to 0.88). Similar results were found for ischaemic stroke; no association was found for haemorrhagic stroke (data for these results was not provided). These associations were only observed among men with a history of hypertension.
  • Intakes of dietary fibre, magnesium and calcium were not associated with the risk of stroke. (Relative risks and 95% confidence intervals: fibre 0.70, 0.48 to 1.00; magnesium 0.70, 0.49 to 1.01; calcium 0.88, 0.63 to 1.23).
  • The association between potassium from supplements and risk of stroke was examined among 1,248 supplement users. In hypertensive men, use of high dose potassium supplements (more than 1 g/d) was associated with a 58% reduced risk of stroke compared with non-supplement use (relative risk 0.42, 95% confidence interval 0.24 to 0.75).
  • In men taking diuretics at baseline, either alone or in combination with other antihypertensive drugs, use of potassium supplements was associated with a 64% reduced risk of stroke compared with non-use (relative risk 0.36, 95% confidence interval 0.18 to 0.72).

Comment

The main risk factor for stroke is increased blood pressure. As increasing potassium intake lowers blood pressure, it is difficult to investigate whether stroke is reduced by the lowered blood pressure or by a direct effect of potassium. Furthermore, it is difficult to isolate the effects of potassium from those of other nutrients found in the same foods.

Some of the effect of potassium on stroke may be independent and some additive to the effect that potassium has on blood pressure. Nevertheless, to reduce the risk of stroke, it makes sense to increase potassium intake. The results also suggest that hypertensive men would benefit from taking potassium supplements. However, these results should be viewed with a great deal of circumspection as only 1,248 participants were supplement users and cases of stroke in the analysis would have been extremely small. Certainly, potassium supplements should only be taken with advice from a general practitioner. The best way to increase potassium intake is to eat more fresh fruit and vegetables, which have many other beneficial effects on health, as well as other potassium-rich foods such as nuts, fish and poultry.

Study 2

Participants were 86,368 women, aged 34 to 59 years, from the US Nurses’ Health Study. Excluded were women with a history of cancer, angina, myocardial infarction, stroke or other cardiovascular diseases. Questionnaires collected information on participants’ lifestyle and medical history in 1980 (which was updated every two years). Food frequency questionnaires, administered in 1980, 1984, 1986 and 1990, assessed dietary intake and supplement use during the previous year. Nutrient intakes were divided into quintiles. Fatal and non-fatal cases of stroke were confirmed by several methods, e.g. medical records and death certificates.

Participants were followed for 14 years, during which time 690 cases of stroke were confirmed (386 ischaemic, 203 haemorrhagic and 101 undetermined).

Results

Median intakes of the nutrients in the lowest and highest quintiles were: potassium 2,017 mg/d and 3,555 mg/d; magnesium 211 mg/d and 381 mg/d; calcium 395 mg/d and 1,145 mg/d.

Women in the highest quintiles were more likely to take multivitamin supplements, were more physically active, consumed more animal protein and polyunsaturated fat and less saturated fat than women in the lowest quintiles.

  • Dietary potassium was associated with a reduced risk of ischaemic stroke, adjusting for age, smoking and history of hypertension (relative risk 0.69, 95% confidence interval 0.50 to 0.95). This association no longer remained after adjusting for several other risk factors, e.g. body mass index and physical activity (relative risk 0.72, 95% confidence interval 0.51 to 1.01).
  • Dietary calcium was associated with a reduced risk of ischaemic stroke, adjusting for age and smoking (relative risk 0.70, 95% confidence interval 0.51 to 0.97). This association disappeared after adjusting for other risk factors, e.g. body mass index, physical activity, history of hypertension (relative risk 0.73, 95% confidence interval 0.53 to 1.01).
  • Dietary magnesium was not associated with the risk of stroke (relative risk 0.79, 95% confidence interval 0.57, 1.10).
  • No associations were found between potassium, magnesium or calcium supplement use and risk of stroke.

Comment

This study further demonstrates how difficult it is to measure the effects of different micronutrients. Whereas there are known mechanisms by which potassium intake can reduce risk of stroke (e.g. potassium lowers blood pressure and the main risk factor for stroke is increased blood pressure), the mechanisms by which calcium intake could reduce the risk of stroke are not apparent.