As food formulators continue to reformulate for lower salt foods, a Harvard-led study adds further support for cutting sodium and boosting potassium intakes.
Writing in the Archives of Internal Medicine, the Boston-based researchers report that higher sodium to potassium excretion ratio, indicative of higher sodium and lower potassium intakes, increases the risk of heart disease by 24 per cent.
The trials of hypertension prevention (TOHP) I and II – looked at the effects of sodium reduction and other interventions on the risk of cardiovascular disease (CVD). Researchers, led by Nancy Cook from Harvard Medical School, found that increasing levels of sodium in the urine increased the risk of CVD.
Salt is of course a vital nutrient and is necessary for the body to function, but campaigners for salt reduction, like the Consensus Action on Salt and Health (CASH) consider the average daily salt consumption in the western world, between 10 and 12g, far too high.
Numerous scientists are convinced that high salt intake is responsible for increasing blood pressure (hypertension), a major risk factor for cardiovascular disease (CVD) - a condition that causes almost 50 per cent of deaths in Europe.
The pressure has been mounting on food manufacturers to reduce the salt content of their foods and the UK's Food Standards Agency's (FSA) recommendation of six grams of salt per day for the general population is understood to be more a realistic target for the next five years than the ideal healthy limit.
“The totality of evidence suggests that lowering dietary sodium intake, while increasing potassium consumption, at the population level might reduce the incidence of CVD,” wrote Cook.
Data from 2275 participants was collected in the trials, including urine samples over 24-hour periods. The participants were adults with pre-hypertension aged between 30 and 54. For TOHP I tested seven non-pharmacologic interventions for 18 months, including lifestyle interventions of weight loss, sodium reduction, and stress management, and supplements of calcium, magnesium, potassium, and fish oil. TOHP II tested the effect of weight loss and sodium reduction over a three year period.
Over the course of the study, 193 CVD events were documented. While no differences were observed for levels of sodium excretion or potassium excretion independently, a significant trend was observed when the researchers considered the sodium to potassium excretion ratio.
“In our study, we found that the sodium to potassium excretion ratio was the strongest […] measure in predicting CVD and that the effect of urinary sodium or potassium excretion was enhanced when the other was included in the model, supporting the notion that the joint activity of these two electrolytes may have an important biologic role,” wrote the researchers.
The sodium to potassium excretion ratio displayed the strongest and statistically significant association, with a 24 per cent increase in risk per unit of the ratio that was similar for CHD and stroke and was consistent across subgroups,” they concluded.
Source: Archives of Internal Medicine
12 January 2009, Volume 169, Number 1, Pages 32-40
"Joint Effects of Sodium and Potassium Intake on Subsequent Cardiovascular Disease - The Trials of Hypertension Prevention Follow-up Study"
Authors: N.R. Cook, E. Obarzanek, J.A. Cutler, J.E. Buring, K.M. Rexrode, S.K. Kumanyika, L.J. Appel, P.K. Whelton, for the Trials of Hypertension Prevention Collaborative Research Group