Potassium, Calcium, and Magnesium Intakes and Risk of Stroke in Women

Susanna C. Larsson; Jarmo Virtamo; Alicja Wolk

Disclosures

Am J Epidemiol. 2011;174(1):35-43. 

In This Article

Discussion

In the present prospective cohort study of Swedish women, we found no overall associations between potassium, calcium, and magnesium intakes and the risk of total stroke or cerebral infarction. However, potassium and magnesium intakes were significantly inversely associated with the risk of cerebral infarction among women with a history of hypertension. In contrast to the hypothesis, calcium intake was positively associated with risk of intracerebral hemorrhage.

Rich food sources of potassium include fruits, vegetables (especially root vegetables), and legumes. Foods high in magnesium include whole grains, legumes, nuts, bananas, and green leafy vegetables.

Findings from previous prospective studies of potassium, calcium, and magnesium intakes in relation to risk of stroke have been inconsistent (Web Table 1, available at http://aje.oxfordjournals.org/). Of the 8 prospective studies that have assessed the association between potassium intake and stroke incidence or mortality,[15–22] 4 showed a significant inverse association.[15,16,18,20] Of the 6 studies of calcium intake in relation to stroke incidence or mortality,[16,17,22–25] 4 found an inverse association between stroke and intake of dairy calcium but not nondairy calcium.[17,23,25,26] No association was observed for total calcium intake from both dairy and nondairy foods.[16,22] A randomized trial that included 36,282 postmenopausal women found no effect of combined calcium and vitamin D supplementation on risk of stroke over a 7-year period.[33] Dietary magnesium intake has been inversely associated with stroke incidence, either overall or in subgroups, in 3[16,22,27] of 5[16,17,22,26,27] previous studies.

Of previous studies that have examined a potential interaction between potassium, calcium, or magnesium intake and history of hypertension in relation to risk of stroke,[16,18,22] 2 showed an interaction.[16,18] In the Health Professionals Follow-up Study, intake of potassium and magnesium but not of calcium was significantly inversely associated with the risk of stroke among men with a history of hypertension but not among men with no history of hypertension.[16] Similarly, a low potassium intake was associated with an increased risk of stroke in hypertensive men but not in nonhypertensive men in the National Health and Nutrition Examination Survey Epidemiologic Follow-up Study.[18] However, no association was observed in women.[18] In the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study, intake of magnesium but not potassium or calcium was inversely associated with risk of cerebral infarction, but the associations were not modified by hypertension.[22]

The reason for the inconsistent results for potassium, magnesium, and calcium intakes in relation to stroke may be differences in the range of exposure or the lack of adjustment for potential confounders. An association may not be seen if the difference in intake between the lowest and highest intake categories is too small. In fact, we observed a statistically significant inverse association between potassium intake and risk of stroke in women in the highest decile of potassium intake compared with those in the lowest decile. Moreover, an association may only be seen in specific subgroups of the population, such as hypertensive individuals, as suggested in the present study and 2 previous studies.[16,18] The inverse association of intake of calcium from dairy foods but not from nondairy sources with stroke incidence or mortality observed in some studies[17,23–25] could suggest that factors other than the calcium in dairy foods account for the observed association.

We observed an unexpected positive association between dietary calcium intake and the risk of intracerebral hemorrhage. This association was in opposition to the one assumed in the hypothesis. Because many analyses were performed, it is possible that this finding was due to chance. No previous study has reported a positive association between calcium intake and intracerebral hemorrhage.

The strengths of this study include the prospective and population-based design and the almost complete follow-up of study participants by linkage with various population-based Swedish registries. Additionally, this study included a large number of incident stroke cases, which led to high statistical power in the analysis. A limitation of this study is that diet was assessed with a self-administered questionnaire, which inevitably led to some measurement error in dietary intake. Thus, we cannot rule out the possibility that the lack of observed association is due to misclassification of exposure, leading to attenuated risk estimates. Another limitation is that our assessment of hypertension was based on self-report, which is less reliable than clinical measurement. Finally, although we controlled for other risk factors for stroke, we cannot exclude the possibility that our results have been affected by residual confounding by imprecisely or unmeasured risk factors.

In conclusion, findings from this prospective cohort study of women suggest that potassium and magnesium intakes are inversely associated with risk of cerebral infarction among women with hypertension. We observed no protective effect of calcium intake on stroke risk.

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