MedicalResearch.com: What is the background for this study?
Response: Studies have shown that there is a strong linear relationship between sodium intake and blood pressure and raised blood pressure is a leading cause of death and disability worldwide.
The current mean population sodium intake among adults in most countries is approximately 4,000 mg/d (10 g/d salt). The World Health Organisation (WHO) has recommended a 30% reduction in sodium intake by 2025 with an eventual target of less than 2,000 mg/d (5 g/d salt) for all countries. Several recent cohort studies have challenged the WHO’s recommendations, as these studies suggested that there was a J or U-shaped relationship between sodium and risk, i.e. lower and higher sodium intake both were associated with an increased risk of cardiovascular events and deaths.
However, these studies have several severe methodological problems, one of which is the use of a biased or unreliable estimate of individual’s usual sodium intake, e.g. a single spot urine with the Kawasaki formula.
Our study, for the first time, has compared the relationship of sodium intake and mortality, based on various methods to assess usual sodium intake, including estimates based on the Kawasaki formula (single and average of multiple days) and a single measured 24-hour urine, with the gold standard method, i.e. the average of multiple non-consecutive measured 24-h urines.
MedicalResearch.com: What are the main findings?
Response: The average measured sodium (gold standard) showed a direct linear relationship with mortality. The estimated sodium intakes changed this linear association. There appeared to be a J-shaped relationship between the average estimated sodium and mortality. A single estimated and single measured sodium both flattened the relationship.
MedicalResearch.com: What should readers take away from your report?
Response: Our study using the gold standard method to assess sodium intake proves that high sodium intake leads to higher death rate, and inaccurate measurement of sodium intake could be an important contributor to the paradoxical J-shaped findings reported in some cohort studies. Therefore, paradoxical results from methodologically flawed studies should not be used to derail critical public health policy, nor divert action.
The totality of evidence shows that reducing salt intake will be immensely beneficial in preventing strokes, heart attacks and heart failure, the commonest causes of death and disability in the world. Every country should develop and implement a coherent workable strategy to reduce population salt intake.
MedicalResearch.com: What recommendations do you have for future research as a result of this work?
Response: Future research should focus on how to effectively reduce population salt intake.
Disclosures: I am a member of Consensus Action on Salt & Health (CASH) and World Action on Salt & Health (WASH). Both CASH and WASH are non-profit charitable organisations and I do not receive any financial support from CASH or WASH.
Feng J He, Norm R C Campbell, Yuan Ma, Graham A MacGregor, Mary E Cogswell, Nancy R Cook. Errors in estimating usual sodium intake by the Kawasaki formula alter its relationship with mortality: implications for public health. International Journal of Epidemiology, 2018; DOI: 10.1093/ije/dyy114
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