Sodium intake in South Africa : an analysis of food supply, 24-hour excretion and blood pressure in a tri-ethnic population

Abstract

Introduction: Currently, 1.13 billion people in the world have increased blood pressure. Low and middle income countries, including South Africa, contribute significantly to this number. The burden caused by hypertension is to a large extent preventable and therefore, serious efforts need to be made by all to address this. Excess dietary sodium intake is associated with increased blood pressure and the reduction of sodium is considered one of the best investments in public health. The South African government has recently implemented a mandatory regulation (R.214) pertaining to the reduction of sodium in foodstuffs as part of a wider sodium reduction strategy. Monitoring of such a strategy is crucial. Objectives: The main aim of this research was to provide insight into the current sodium and potassium intake of South Africans. Specific objectives included (i) establishing baseline sodium and potassium intake values; (ii) investigating alternative methodology for sodium intake in South Africans and (iii) evaluating the sodium content in foodstuffs and reporting on the food industry’s compliance with the targets set in the regulation. Methods: For the population’s sodium intake, 24-hour urine samples and spot urine samples were collected from three different population groups i.e. White, Black and Indian. Sodium, potassium and iodine were analysed using appropriate methods. Three different formulas were used to estimate sodium excretion i.e. Kawasaki, Tanaka and INTERSALT. To evaluate the sodium content of foodstuffs we randomly selected ten food products from each of the 13 food categories and measured the sodium content by means of an atomic absorption spectrometer. Results: In total, 692 successful 24-hour urine collections and 681 spot urine samples were collected. The median sodium and potassium excretion was 122.9 and 33.5mmol/day, respectively and the median calculated salt intake was 7.2g/day. The majority (92.8%) of the population did not meet the recommended potassium intake per day and 65.6% consumed more than 6g of salt per day. The median sodium-to-potassium ratio was 3.5. Individuals in the lowest salt intake category still had significant iodine levels. The Kawasaki and the Tanaka formulas showed significantly higher estimated sodium values than the measured 24-hour excretion in the whole population (5677.79mg/d and 4235.05mg/d vs. 3279.19mg/d) whereas the INTERSALT formula did not differ. The Kawasaki formula also showed the highest degree of bias (-2242mg/d, 95% CI: -10659 – 6175) in comparison with the INTERSALT, which had the lowest (161mg/d, -4038 – 4360). In terms of the sodium content of the foodstuffs, 72% of the food products tested comply with the targets for 2016 and 42% of the products with the 2019 targets. All of the food categories, except for “flavoured potato crisp” and “flavoured salt-and-vinegar snacks”, complied with the 2016 target. Conclusion: These findings support the South African government’s motivation for a sodium reduction strategy. The sodium excretion estimations of the three formulas should be used with caution when reporting on sodium intake levels. More research is needed to validate and develop a specific formula for South Africans. The sodium content in foodstuffs can serve as a baseline for monitoring compliance over the next few years