Estimating population salt intake in India using spot urine samples
Kristina S Petersen1, Claire Johnson, Sailesh Mohan
1aThe George Institute for Global Health bThe University of Sydney, Sydney, Australia cPublic Health Foundation of India dCentre for Chronic Disease Control, New Delhi eGeorge Institute for Global Health, Hyderabad, India fWolfson Institute of Preventive Medicine, Barts and The London School of Medicine & Dentistry, Queen Mary University of London, London, UK gAll India Institute of Medical Sciences, New Delhi, India hGeorge Institute for Global Health, University of Oxford, Oxford, UK iCharles Perkins Centre, University of Sydney, Sydney, Australia jImperial College, London, UK kRoyal Prince Alfred Hospital, Sydney, Australia.
Objective:
To compare estimates of mean population salt intake in North and South India derived from spot urine samples versus 24-h urine collections.
Methods:
In a cross-sectional survey, participants were sampled from slum, urban and rural communities in North and in South India. Participants provided 24-h urine collections, and random morning spot urine samples. Salt intake was estimated from the spot urine samples using a series of established estimating equations. Salt intake data from the 24-h urine collections and spot urine equations were weighted to provide estimates of salt intake for Delhi and Haryana, and Andhra Pradesh.
Results:
A total of 957 individuals provided a complete 24-h urine collection and a spot urine sample. Weighted mean salt intake based on the 24-h urine collection, was 8.59 (95% confidence interval 7.73-9.45) and 9.46 g/day (8.95-9.96) in Delhi and Haryana, and Andhra Pradesh, respectively. Corresponding estimates based on the Tanaka equation [9.04 (8.63-9.45) and 9.79 g/day (9.62-9.96) for Delhi and Haryana, and Andhra Pradesh, respectively], the Mage equation [8.80 (7.67-9.94) and 10.19 g/day (95% CI 9.59-10.79)], the INTERSALT equation [7.99 (7.61-8.37) and 8.64 g/day (8.04-9.23)] and the INTERSALT equation with potassium [8.13 (7.74-8.52) and 8.81 g/day (8.16-9.46)] were all within 1 g/day of the estimate based upon 24-h collections. For the Toft equation, estimates were 1-2 g/day higher [9.94 (9.24-10.64) and 10.69 g/day (9.44-11.93)] and for the Kawasaki equation they were 3-4 g/day higher [12.14 (11.30-12.97) and 13.64 g/day (13.15-14.12)].
Conclusion:
In urban and rural areas in North and South India, most spot urine-based equations provided reasonable estimates of mean population salt intake. Equations that did not provide good estimates may have failed because specimen collection was not aligned with the original method.
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