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

Introduction: Attempting 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 analysis: Baseline 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 dissemination: SAGE 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.