Leveraging ongoing research to evaluate the health impacts of South Africa's salt reduction strategy: a prospective nested cohort within the WHO-SAGE multicountry, longitudinal study

Abstract

IntroductionAttempting to curb the rising epidemic of hypertension, South Africa implemented legislation in June 2016 mandating maximum sodium levels in a range of manufactured foods that contribute significantly to population salt intake. This natural experiment, comparing two African countries with and without salt legislation, will provide timely information on the impact of legislative approaches addressing the food supply to improve blood pressure in African populations. This article outlines the design of this ongoing prospective nested cohort study.Methods and analysisBaseline sodium intake was assessed in a nested cohort of the WHO Study on global AGEing and adult health (WHO-SAGE) wave 2 (2014–2015), a multinational longitudinal study on the health and well-being of adults and the ageing process. The South African cohort consisted of randomly selected households (n=4030) across the country. Spot and 24-hour urine samples are collected in a random subsample (n=1200) and sodium, potassium, creatinine and iodine analysed. Salt behaviour and sociodemographic data are captured using face-to-face interviews, alongside blood pressure and anthropometric measures. Ghana, the selected control country with no formal salt policy, provided a nested subsample (n=1200) contributing spot and 24-hour urine samples from the SAGE Ghana cohort (n=5000). Follow-up interviews and urine collection (wave 3) in both countries will take place in 2017 (postlegislation) to assess change in population-level sodium intake and blood pressure.Ethics and disseminationSAGE was approved by the WHO Ethics Review Committee (reference number RPC149) with local approval from the North-West University Human Research Ethics Committee and University of the Witwatersrand Human Research Ethics Committee (South Africa), and University of Ghana Medical School Ethics and Protocol Review Committee (Ghana). The results of the study will be published in peer-reviewed international journals, presented at national and international conferences, and summarised as research and policy briefs.

Cervical cancer screening practices among women in Ghana: evidence from wave 2 of the WHO study on global AGEing and adult health

“…The World Health Organization and the University of Ghana Medical School through the Department of Community Health collaborated to implement the Wave 2 of the study between 2014 and 2015. The methods used in the survey is available elsewhere [12].…”

Salt Use Behaviours of Ghanaians and South Africans: A Comparative Study of Knowledge, Attitudes and Practices

“…In selecting the sample, all SAGE Wave 1 households were included for SAGE Wave 2 data collection [ 45 ]. In SAGE SA, replacements for sample attrition used a systematic sampling approach to randomly select new households as previously described [ 46 ]. The sampling method used in SAGE Ghana followed a similar design, based on the 2003 World Health Survey/SAGE Wave 0 [ 47 ] with primary sampling units (PSUs) stratified by region and location (urban/rural).…”

Prediction of 24-hour sodium excretion from spot urine samples in South African adults: a comparison of four equations

“…This analysis is based on data collected in a sub-study [35] of the World Health Organisation Study on global AGEing and adult health (WHO-SAGE, Wave 2). WHO-SAGE is a multinational longitudinal study examining the health and wellbeing of adult populations and the ageing process in over 42,000 respondents from six countries (China, Ghana, India, Mexico, Russia, and South Africa) [36].…”

“…Spot and 24-hour urine collection was conducted in a nested subsample of Wave 2 respondents alongside the standard WHO-SAGE data collection (household, individual, and proxy questionnaires; anthropometry; dried blood spot collection; BP; and physical function tests [36,38]). The WHO/PAHO protocol was used for sodium determination in 24-hour urine [39], with the detailed protocol described previously [35]. In brief, respondents were requested to collect all urine produced for 24-hours, excluding the first pass urine on day 1, but including the first urine of the following morning (day 2) in a 5-litre plastic container containing 1 g thymol as preservative.…”