Prospective study of calcium, potassium, and magnesium intake and risk of stroke in women

Background and Purpose-High intakes of calcium, potassium, and magnesium ha ve been hypothesized to reduce risks of cardiovascular disease, but only a few prospective studies have examined intakes of these cations in relation to risk of stroke. Methods-In 1980, 85 764 women in the Nurses' Health Study cohort, aged 34 t o 59 years and free of diagnosed cardiovascular disease and cancer, complet ed dietary questionnaires from which we calculated intakes of calcium, pota ssium, and magnesium. By 1994, after 1.16 million person-years of follow-up , 690 incident strokes (129 subarachnoid hemorrhages, 74 intraparenchymal h emorrhages, 386 ischemic strokes, and 101 strokes of undetermined type) had been documented. Results-Intakes of calcium, potassium, and magnesium were each inversely as sociated with age- and smoking-adjusted relative risks of ischemic stroke, excluding embolic infarction of nonatherogenic origin (n=347), Adjustment f or other cardiovascular risk factors, including history of hypertension, at tenuated these associations, particularly for magnesium intake. In a multiv ariate analysis, women in the highest quintile of calcium intake had an adj usted relative risk of ischemic stroke of 0.69 (95% CI, 0.50 to 0.95; P for trend=0.03) compared with those in the lowest quintile; for potassium inta ke the corresponding relative risk was 0.72 (95% CI, 0.51 to 1.01; P for tr end=0.10). Further simultaneous adjustment for calcium and potassium intake suggested an independent association for calcium intake, The association o f risk with calcium intake did not appear to be log linear; the increase in risk was limited to the lowest quintile of intake, and intakes >approximat e to 600 mg/d did not appear to reduce risk of stroke further. The inverse association with calcium intake was stronger for dairy than for nondairy ca lcium intake. Intakes of calcium, potassium, and magnesium were not related to risk of other stroke subtypes. Conclusions-Low calcium intake, and perhaps low potassium intake, may contr ibute to increased risk of ischemic stroke in middle-aged American women. I t remains possible that women in the lowest quintile of calcium intake had unknown characteristics that made them susceptible to ischemic stroke.