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Research
Salt intake, stroke, and cardiovascular disease: meta-analysis of
prospective studies
Pasquale Strazzullo, professor of medicine1, Lanfranco D’Elia, clinical
lecturer in medicine1, Ngianga-Bakwin
Kandala, principal research fellow in medical statistics2, Francesco P
Cappuccio, professor of cardiovascular medicine and epidemiology2
1 Department of Clinical and Experimental Medicine, "Federico II"
University of Naples Medical School, Naples, Italy, 2 University of Warwick,
WHO Collaborating Centre for Nutrition, Warwick Medical School, Clinical
Sciences Research Institute, Coventry CV2 2DX
Correspondence to: P Strazzullo strazzul@unina.it,
FP Cappuccio f.p.cappuccio@warwick.ac.uk
Objective To assess the relation between the level of habitual
salt intake and stroke or total cardiovascular disease outcome.
Design Systematic review and meta-analysis of prospective
studies published 1966-2008.
Data sources Medline (1966-2008), Embase (from 1988), AMED
(from 1985), CINAHL (from 1982), Psychinfo (from 1985), and the Cochrane
Library.
Review methods For each study, relative risks and 95%
confidence intervals were extracted and pooled with a random effect model,
weighting for the inverse of the variance. Heterogeneity, publication bias,
subgroup, and meta-regression analyses were performed. Criteria for inclusion
were prospective adult population study, assessment of salt intake as baseline
exposure, assessment of either stroke or total cardiovascular disease as
outcome, follow-up of at least three years, indication of number of
participants exposed and number of events across different salt intake categories.
Results There were 19 independent cohort samples from 13
studies, with 177 025 participants (follow-up 3.5-19 years) and over 11 000
vascular events. Higher salt intake was associated with greater risk of stroke
(pooled relative risk 1.23, 95% confidence interval 1.06 to 1.43; P=0.007) and
cardiovascular disease (1.14, 0.99 to 1.32; P=0.07), with no significant
evidence of publication bias. For cardiovascular disease, sensitivity analysis
showed that the exclusion of a single study led to a pooled estimate of 1.17
(1.02 to 1.34; P=0.02). The associations observed were greater the larger the
difference in sodium intake and the longer the follow-up.
Conclusions High salt intake is associated with significantly
increased risk of stroke and total cardiovascular disease. Because of
imprecision in measurement of salt intake, these effect sizes are likely to be
underestimated. These results support the role of a substantial population
reduction in salt intake for the prevention of cardiovascular disease.