Salt May Lower Blood Pressure in Some People

A new study suggests that the association of sodium intake with cardiovascular disease (CVD) is valid only when mean intake is greater than 5 g/day, and with lower intake, the inverse relationship may be true.

Researchers at McMaster University (Hamilton, ON, Canada), King Saud University (KSU; Riyadh, Saudi Arabia), Aga Khan University (Karachi, Pakistan), and other institutions from 21 countries participating in the Prospective Urban Rural Epidemiology study explored community-level associations between sodium and potassium intake and blood pressure (BP) in 369 communities and CVD and mortality in 255 communities, using morning fasting urine to estimate 24-hour sodium and potassium excretion as a surrogate for intake.

During the study period, there were 3.8% deaths and 4.2% cardiovascular events, including heart attack, stroke, heart failure. Mean sodium intake and major cardiovascular events showed a significant inverse association in the lower third of sodium intake, no association in the middle third, and a positive, non-significant association in the highest third. When aggregated by communities, increased sodium intake was strongly associated with increased BP, with blood pressure increasing by nearly three mm Hg for each ½ teaspoon of salt.

But adjustments for age, gender, country, and other factors resulted in no association of sodium intake and heart attacks, cardiac deaths or the composite score. In fact, in those communities with lower salt intake, the inverse relationship was seen; increased salt lowered BP, for both systolic and diastolic BP values. Community aggregated potassium intake, on the other hand, showed an inverse relationship in all countries. All major cardiovascular outcomes decreased with increasing potassium intake, and appeared protective from cardiovascular events. The study was published on August 11, 2018, in The Lancet.

“Most previous studies relating sodium intake to heart disease and stroke were based on individual-level information; public health strategies should be based on best evidence. There is no convincing evidence that people with moderate or average sodium intake need to reduce their sodium intake for prevention of heart disease and stroke,” said co-lead author Martin O'Donnell, MD, of McMaster University. “Community-level interventions to reduce sodium intake should target communities with high sodium consumption, and should be embedded within approaches to improve overall dietary quality.”

The World Health Organization (WHO) recommends consumption of less than two gram/day of sodium as a preventive measure against CVD, but this target has not been achieved in any country. The recommendation is primarily based on individual-level data from short-term trials of blood pressure, without data relating low sodium intake to reduced cardiovascular events from randomized trials or observational studies.

Related Links:
McMaster University
King Saud University
Aga Khan University