Pinch of salt: How much is enough?

By Dr. Ananya Mandal, MDOct 21 2010

Dietary salt restriction is in the spotlight again. While scientists are questioning the complex role of sodium in the body and the need for salt restriction, surveys have found that dietary sodium has not gone down well in large populations despite awareness on the risks of too much salt intake.

A comprehensive survey of salt intake in the US found salt consumption had not changed in more than 40 years, despite the recent rise of low-sodium foods, and the average was at least 50 per cent higher than the recommended maximum. Also there was limited movement of dietary salt intake in the population. This means that people naturally gravitate towards a similar amount of dietary salt, regardless of changes in food processing.

The study was led by the eminent Harvard researcher Walter Willett. He and his team analyzed all studies between 1957 and 2003 that measured sodium levels in urine - a more accurate method than asking people what foods they ate. This showed that while salt intake had not changed prevalence of high blood pressure had risen. This may mean that the “epidemic of obesity may be a more plausible determinant.” The study was published in the American Journal of Clinical Nutrition.

One of the co-authors David McCarron said that that study showed that blanket public recommendations to eat a low salt diet, aimed at all people and not just those at highest risk of heart disease, were “doomed to failure”. Only one fourth of the daily salt intake comes from non-processed food and thus many health authorities believe persuading manufacturers to lower salt content would benefit health. But Dr McCarron said “working against that theoretical outcome is the reality that over millennia…sodium was added to food at the time of preservation, cooking or consumption,” and if salt were removed from processing people might simply seek it elsewhere. This tendency to maintain a stable salt intake might be just “evidence of a ‘normal’ range of dietary sodium intake in humans that is consistent with our understanding” of the functions of salt, such as its regulation of blood volume, Dr McCarron said.

According to Susan Anderson, the director for healthy weight at the Heart Foundation, salt does have an effect on blood pressure enough to justify public recommendations. She added, “Australia has well over two million people [with high blood pressure] and we think it could be double that…When you're looking at those sort of numbers, one of your approaches still has to be a population approach.”

Food Standards Australia New Zealand is currently reviewing nutrient guidelines and has proposed the recommended adult daily maximum of 2300 milligrams could be revised down to 1600 or even 920 milligrams. Researcher Dr. Adam Bernstein, a research fellow in the department of nutrition at Harvard School of Public Health in Boston also added, “We would support the recommendation for 1,500 milligrams-a-day intake.”

This week, Calgary hosted the second of three WHO conferences on Population Sodium Reduction Strategies. The conference ended Wednesday and looked at ways to assess salt consumption and evaluate programs aimed at reducing sodium intake. Dr. Norm Campbell, co-chairman of the conference and University of Calgary Faculty of Medicine professor said, “Countries need to know how much salt is consumed, where in the diet the salt comes from and how to determine the effectiveness of national programs to reduce salt.”

A Health Canada-led sodium working group has proposed people cut their sodium intake to 2,300 milligrams per day, from the current daily average of 3,400 mg by 2016. The ultimate goal is to get Canadians down to the recommended daily limit of 1,500 mg.