Relationship of urinary sodium/potassium excretion and calcium intake to blood pressure and prevalence of hypertension among older Chinese vegetarians

Abstract

Objective: To examine the associations of dietary sodium and potassium, as reflected by the urinary sodium/potassium excretion, and calcium intake with blood pressure and the prevalence of hypertension among older Chinese vegetarians in Hong Kong. Design: Cross-sectional study. Setting: Research clinic in a teaching hospital in Hong Kong. Subjects: A total of 111 ambulatory vegetarians over the age of 55 were recruited from members of religious organizations or old age hostels. Main outcome measures: Hypertension was defined as supine blood pressure >140/90 mmHg or a history of hypertension. Dietary sodium, potassium and calcium intakes were assessed by 24 h recall method or fasting urinary sodium or potassium/creatinine ratios. Results: Seventy-one subjects (64%) were found to have hypertension. Compared with normotensive subjects, hypertensive subjects had lower calcium intake (411±s.d. 324 vs 589±428 mg, P=0.04), but higher urinary sodium/creatinine ratio (32.6±19.3 vs 21.0±12.4, P=0.00) and sodium/potassium ratio (4.7±2.8 vs 3.4±2.3, P=0.02). Among 88 subjects not taking diuretics or antihypertensive drugs, systolic blood pressure was related to calcium intake (r=−0.40), urinary sodium/creatinine ratio (r=0.39), urinary sodium/potassium ratio (r=0.30) and age (r=0.23). Diastolic blood pressure was related to urinary sodium/creatinine (r=0.29). Twenty-three subjects with high urinary sodium/potassium and low calcium intake and 16 subjects with low urinary sodium/potassium ratio and high calcium intake differed markedly with respect to systolic blood pressure (159±26 vs 130±15 mmHg) and prevalence of hypertension (78% vs 25%). Conclusion: Older Chinese vegetarians are predisposed to hypertension because of their sodium-rich but calcium-deficient diets.