Journal of Human Hypertension
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April 2001, Volume 15, Number 4, Pages 229-237
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Original Article
Urinary calcium excretion, sodium intake and blood pressure in a multi-ethnic population: results of the Wandsworth Heart and Stroke Study
A M Blackwood1, G A Sagnella1, D G Cook2 and F P Cappuccio3

1Department of Medicine, St George's Hospital Medical School, Cranmer Terrace, London SW17 0RE, UK

2Department of Public Health Sciences, St George's Hospital Medical School, Cranmer Terrace, London SW17 0RE, UK

3Department of General Practice and Primary Care, St George's Hospital Medical School, Cranmer Terrace, London SW17 0RE, UK

Correspondence to: Francesco P Cappuccio, Professor of Primary Care Research and Development, Department of General Practice & Primary Care, St George's Hospital Medical School, Cranmer Terrace, London SW17 0RE, UK. E-mail f.cappuccio@sghms.ac.uk

Abstract

Background: Hypertension is associated with increased urinary calcium excretion (UCa). A high sodium intake increases both UCa and blood pressure (BP). However, it is not clear whether these effects are modified by gender or ethnic origin.

Objectives: To examine the relationships between BP, urinary sodium (UNa), gender and ethnic origin with both daily and fasting UCa in a population-based study.

Design and Methods: Out of 1577 individuals taking part in a cross-sectional survey, 743 were considered for the present analysis (407 women, 336 men) as they were all untreated, had provided a complete 24-h urine collection, and had all measurements of anthropometry, BP, UNa and UCa. They were 277 whites, 227 of black African origin and 239 South Asians. Comparisons were also carried out in the 690 participants who also provided 3-h fasting urine collections.

Results: After adjustment for confounders including age, and gender, 24-h UCa was significantly and independently associated with ethnic origin, BP and UNa. Mean 24-h UCa was 4.62 (s.e. 0.11) mmol/d in whites, 3.33 (0.12) in South Asians and 3.16 (0.13) in blacks (P < 0.001). a 100 mmol higher UNa predicted a 1.04 mmol higher daily UCa (P < 0.001), and a 20 mm Hg higher systolic BP predicted a 0.28 mmol higher UCa. The slopes were not significantly different by ethnic group. The ethnic differences in UCa were present when fasting UCa was used instead (1.64 [0.05] mumol/min in whites, 1.08 [0.06] in South Asians and 1.13 [0.06] in blacks; P < 0.001).

Conclusions: These results indicate that BP, salt intake and ethnic origin are independent predictors of UCa in an unselected population. These relationships are unlikely to be the result of differences in Ca intake or intestinal Ca absorption as they are seen also after an overnight fast, suggesting that they may reflect differences in renal tubular handling. The estimated effects of either BP or sodium intake on UCa, sustained over many years, may be associated with significant effects on bone calcium content.

Journal of Human Hypertension (2001) 15, 229-237

Keywords

urinary calcium; dietary sodium; blood pressure; ethnic origin

Received 13 September 2000; revised 13 November 2000; accepted 13 November 2000
April 2001, Volume 15, Number 4, Pages 229-237
Table of contents    Previous  Abstract  Next   Article  PDF