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(Stroke. 2002;33:1178.)
© 2002 American Heart Association, Inc.

Letters to the Editor

Race and Sex Differences in the Effects of Dietary Potassium Intake on the Risk of Stroke

Shinji Fukui, MD; Naoki Otani, MD; Nobusuke Tsuzuki, MD, DMSc; Hiroshi Nawashiro, MD, DMSc Katsuji Shima, MD, DMSc

Department of Neurosurgery, National Defense Medical College, Tokorozawa, Japan

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.

References

1. Fang J, Madhavan S, Alderman MH. Dietary potassium intake and stroke mortality. Stroke. 2000; 31: 1532–1537.[Abstract/Free Full Text]
2. Bazzano LA, He J, Ogden LG, Loria C, Vupputuri S, Myers L, Whelton PK. Dietary potassium intake and risk of stroke in US men and women: National Health and Nutrition Examination Survey I epidemiologic follow-up study. Stroke. 2001; 32: 1473–1480.[Abstract/Free Full Text]
3. Ascherio A, Rimm EB, Giovannucci EL, Colditz GA, Rosner B, Willett WC, Sacks F, Stampfer MJ. A prospective study of nutritional factors and hypertension among US men. Circulation. 1992; 86: 1475–1484.[Abstract/Free Full Text]
4. Pamnani MB, Chen X, Haddy FJ, Schooley JF, Mo Z. Mechanism of antihypertensive effect of dietary potassium in experimental volume expanded hypertension in rats. Clin Exp Hypertens. 2000; 22: 555–569.
5. Siani A, Strazzullo P, Giacco A, Pacioni D, Celentano E, Mancini M. Increasing the dietary potassium intake reduces the need for antihypertensive medication. Ann Intern Med. 1991; 115: 753–759.
6. Clegg G, Morgan DB, Davidson C. The heterogeneity of essential hypertension: relation between lithium efflux and sodium content of erythrocytes and a family history of hypertension. Lancet. 1982; 2: 891–894.[Medline] [Order article via Infotrieve]
7. Blaustein MP. Sodium ions, calcium ions, blood pressure regulation, and hypertension: a reassessment and a hypothesis. Am J Physiol. 1977; 232: C165–C173.[Abstract/Free Full Text]
8. Munro-Faure AD, Hill DM, Anderson J. Ethnic differences in human blood cell sodium concentration. Nature. 1971; 231: 457–458.[CrossRef][Medline] [Order article via Infotrieve]
9. Beilin LJ, Knight GJ, Munro-Faure AD, Anderson J. The sodium, potassium, and water contents of red blood cells of healthy human adults. J Clin Invest. 1966; 45: 1817–1825.
10. Lasker N, Hopp L, Grossman S, Bamforth R, Aviv A. Race and sex differences in erythrocyte Na+, K+, and Na+-K+-adenosine triphosphatase. J Clin Invest. 1985; 75: 1813–1820.

Lydia Bazzano, PhD Jiang He, MD, PhD

Department of Epidemiology, Tulane University School of Public Health and Tropical Medicine, New Orleans, Louisiana

Response

We thank Dr Fukui and colleagues for their interest in our work. Their discussion of possible mechanisms for race and sex differences in the blood pressure-lowering effect of dietary potassium intake is intriguing.¹ In a meta-analysis of 33 randomized controlled trials, we found that oral potassium supplementation reduced blood pressure significantly in both hypertensive and normotensive participants and in both black and white subjects.² Moreover, the blood pressure reduction was greater in hypertensives compared with normotensives and in blacks compared with whites. Most studies included in the meta-analysis did not show gender differences in blood pressure reduction related to potassium supplementation.

Very few prospective cohort studies have examined the relationship between dietary potassium intake and stroke incidence and mortality. Khaw and Barett-Connor conducted one of the earliest population-based prospective cohort studies to report a significant inverse relationship between dietary potassium intake and stroke mortality among 859 male and female white retirees in Southern California.³ They found a slightly stronger relationship between dietary intake of potassium and stroke mortality in women than in men, irrespective of hypertensive status. In the Health Professionals’ Follow-up Study that included 43 738 middle-aged, predominantly-white men, Ascherio and colleagues documented an inverse relationship between the risk of stroke and dietary potassium intake.⁴ Fang and colleagues examined the relationship between dietary potassium intake and stroke mortality in the First National Health and Nutrition Examination Survey Epidemiologic Follow-up Study (NHEFS) and found an inverse association between dietary potassium intake and stroke mortality in black men and hypertensive men.⁵ In our analysis, we reported a significantly increased stroke incidence among participants who consumed less than 34.6 mmol of potassium per day.⁶ This relationship was independent of age, gender, race, and other important risk factors for stroke.

Findings from our study and from other prospective cohort studies suggest that dietary potassium intake may be related to a lower risk of stroke in blacks and whites and in men and women. However, definitive evidence of a causal relationship between potassium intake and a reduced risk of stroke should come from randomized controlled trials. On the basis of current evidence that potassium lowers blood pressure and that reduced blood pressure lowers stroke risk, it is reasonable to recommend high-potassium foods, such as fruits and vegetables, to the general population with the aim of reducing the societal burden of stroke in the United States and worldwide.

References

1. Fukui S, Otani N, Tsuzuki N, Nawashiro H, Shima K. Race and sex differences in the effects of dietary potassium intake on the risk of stroke. Stroke. 2002; 33: 1178.Letter.[Free Full Text]
2. Whelton PK, He J, Cutler JA, Brancati FL, Appel LJ, Follmann D, Klag MJ. Effects of oral potassium on blood pressure: meta-analysis of randomized, controlled clinical trials. JAMA. 1997; 277: 1624–1632.[Abstract]
3. Khaw K, Barett-Connor E. Dietary potassium and stroke-associated mortality. N Engl J Med. 1987; 316: 235–240.[Abstract]
4. Ascherio A, Rimm EB, Hernan MA, Giovannucci EL, Kawachi I, Stampfer MJ, Willett WC. Intake of potassium, magnesium, calcium, and fiber and risk of stroke among US men. Circulation. 1998; 98: 1198–1204.[Abstract/Free Full Text]
5. Fang J, Madhavan S, Alderman MH. Dietary potassium intake and stroke mortality. Stroke. 2000; 31: 1532–1537.
6. Bazzano LA, He J, Ogden LG, Vupputuri S, Loria C, Myers L, Whelton PK. Dietary potassium intake and risk of stroke in US men and women: NHANES I Epidemiologic Follow-Up Study. Stroke. 2001; 32: 1473–1480.

This article has been cited by other articles:

				S. Fukui, N. Otani, N. Tsuzuki, H. Nawashiro, K. Shima, L. Bazzano, and J. He Race and Sex Differences in the Effects of Dietary Potassium Intake on the Risk of Stroke Stroke, May 1, 2002; 33(5): 1178 - 1179. [Full Text] [PDF]

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Fukui, S. Articles by He, J. Search for Related Content PubMed PubMed Citation Articles by Fukui, S. Articles by He, J. Pubmed/NCBI databases Compound via MeSH Substance via MeSH Hazardous Substances DB SODIUM Medline Plus Health Information Stroke