Race and sex differences in the effects of dietary potassium intake on the risk of stroke.

Race and Sex Differences in the Effects of Dietary Potassium Intake on the Risk of Stroke To the Editor: We read with great interest the 2 articles by Fang et al1 and Bazzano et al2 on the association between dietary potassium intake and stroke mortality. The study by Fang et al has revealed an inverse association between hazard of stroke death and dietary potassium intake in hypertensive men and black men only. On the other hand, Bazzano et al have shown that there was no significant difference in the relation of dietary potassium intake to hazard of stroke that was due to ethnicity or hypertensive status. We would agree with Bazzano et al that their findings of an independent relationship between low potassium intake and increased hazard of stroke in a representative sample of the US population have important clinical and public health implications. However, we believe that the race and sex differences in the effects of dietary potassium intake on the risk of stroke, which was reported by Fang et al, also have important clinical implications as mentioned below. Recent clinical, experimental, and epidemiologic evidences suggested that dietary potassium intake is inversely related to blood pressure.3–5 Therefore, considering that hypertension is the most important known risk factor for stroke, dietary potassium intake may be inversely related to the risk of stroke via blood pressure. Clegg et al6 showed that the sodium concentration of erythrocytes from patients with untreated essential hypertension was higher than that of normotensive control subjects. Furthermore, recent evidence has demonstrated that the high dietary potassium intake lowered the blood pressure in the hypertensive rats, associated with the increase of erythrocyte Na -K -ATPase activity.4 These findings indicate that high dietary potassium intake decreases intracellular sodium concentration, which will result in lowering of blood pressure. An intracellular sodium concentration is thought to have a paramount role in the contractility of vascular smooth muscle cells; an increase in its concentration favors the contraction process.7 However, erythrocytes have been used routinely to examine the intracellular sodium homeostasis of hypertensive patients because human vascular smooth muscle cells are not readily available. Several studies showed that the sodium concentration in erythrocytes from normotensive blacks was higher than that of their white counterparts8 and that erythrocytes of normotensive men had a higher sodium concentration than those from women.9 Since essential hypertension is more common in blacks and men as compared with whites and women of premenopausal age, and because increased sodium concentration has frequently been demonstrated in erythrocytes of hypertensive patients, it is possible that the higher erythrocyte sodium concentration in blacks and men reflects differences in the cellular regulation of sodium, which increase the likelihood of developing hypertension. Lasker et al10 revealed that the erythrocyte Na -K -ATPase activity was lower in blacks and men as compared with their counterparts, namely, whites and women, while the sodium concentration in erythrocytes from blacks and men was higher than that of their counterparts, and that there was a significant inverse correlation between the Na -K -ATPase activity and erythrocyte sodium concentration. These differences based on race and sex in the erythrocyte sodium concentration may have important clinical implications in establishing the useful indication of high dietary potassium intake in the future. We think that a high potassium diet should be indicated for hypertensive patients whose erythrocytes demonstrate a high sodium concentration. However, further studies are required to assess the optimal sodium concentration in erythrocytes of hypertensive patients that can be applied to the indication of high dietary potassium intake.