Sodium Reduction Legislation and Urinary Sodium and Blood Pressure in South Africa
Importance
Reductions in dietary salt are associated with blood pressure reductions; however, national governments that have passed laws to reduce sodium intake have not measured these laws’ impact.
Objective
To determine if South African regulations restricting sodium content in processed foods were associated with reductions in sodium consumption and blood pressure.
Design, Setting, and Participants
The HAALSI (Health and Aging in Africa: A Longitudinal Study of an INDEPTH Community in South Africa) study is a population-based cohort study among adults aged 40 years or older randomly selected from individuals living in rural Mpumalanga Province in South Africa. This study incorporated 3 waves of data (2014/2015, 2018/2019, and 2021/2022) from the HAALSI study to examine how 24-hour urine sodium (24HrNa) excretion changed among a population-based cohort following mandatory sodium regulations. Spot urine samples were collected across 3 waves, and data analysis was performed from 2023 to 2024.
Exposures
South African regulations introduced in 2013 that reduced levels for the maximum amount of sodium in milligrams per 100 mg of food product by 25% to 80% across 13 processed food categories by 2019.
Main Outcomes and Measures
24HrNa was estimated using the INTERSALT equation, and generalized estimating equations were used to assess changes in sodium excretion and blood pressure.
Results
Among 5059 adults 40 years or older, mean (SD) age was 62.43 years (13.01), and 2713 participants (53.6%) were female. Overall mean (SD) estimated 24HrNa excretion at baseline was 3.08 g (0.78). There was an overall reduction in mean 24HrNa excretion of 0.22 g (95% CI, −0.27 to −0.17; P < .001) between the first 2 waves and a mean reduction of 0.23 g (95% CI, −0.28 to −0.18; P < .001) between the first and third waves. The reductions were larger when analysis was restricted to those with samples in all 3 waves (−0.26 g for both waves 2 and 3 compared to wave 1). Every gram of sodium reduction was associated with a −1.30 mm Hg reduction (95% CI, 0.65-1.96; P = .00) in systolic blood pressure. The proportion of the study population that achieved ideal sodium consumption (<2 g per day) increased from 7% to 17%.
Conclusion and Relevance
In this cohort study, following South African regulations limiting sodium in 13 categories of processed foods, there was a significant reduction in 24HrNa excretion among this rural South African population, which was sustained with reductions in blood pressure consistent with levels of sodium excreted. These results support the potential health effects anticipated by effective implementation of population-based salt reformulation policies.
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