Regularly Adding Salt to Food May Shorten Life Span

People who usually or always reach for the salt shaker at mealtime may be taking years off their lives, an analysis of UK Biobank data suggests.

The risk of premature mortality—dying before age 75—was greater among those who reported adding salt to their food more frequently (P < 0.001 for trend), according to researchers led by Hao Ma, MD, PhD (Tulane University School of Public Health and Tropical Medicine, New Orleans, LA).

Moreover, at age 50, women and men who said they always add salt to their food had a life expectancy that was 1.50 and 2.28 years, respectively, lower compared with their peers who never salt their food.

“This is the first study reporting [that a] high frequency of adding salt to foods is related to high risk of premature death,” senior author Lu Qi, MD, PhD (Tulane University School of Public Health and Tropical Medicine and Harvard T.H. Chan School of Public Health, Boston, MA), told TCTMD via email.

Addressing potential mechanisms, he noted that prior studies have indicated that high sodium intake may raise blood pressure, adding that increased salt intake may also affect inflammation and influence the risk of premature mortality through other pathways.

The findings, published online ahead of print in the European Heart Journal, “suggest a behavior related to sodium intake—adding salt to foods—is related to health,” Qi said. “Because our study is the first reporting such a relation, further investigations are needed to confirm our findings before providing recommendations.”

The Great Salt Debate

The impact of various levels of dietary sodium or salt remains a hotly debated issue, driven by conflicting lines of evidence. Much of the work to date has linked higher sodium consumption to worse outcomes, including documenting a direct linear relationship between intake and all-cause mortality. Another recent analysis, by contrast, actually showed greater sodium intake tracking with reduced mortality and longer life expectancy. Nevertheless, international societies and public health agencies, including the American Heart Association, the European Society of Cardiology, and the World Health Organization, recommend at least some level of dietary sodium restriction, generally to below about 5 grams of salt (or 2.3 grams of sodium) per day.

Ma, Qi, and colleagues took a different approach to explore the link between dietary salt intake and clinical outcomes by looking at individuals’ reported use of added salt at mealtime, which accounts for 6% to 20% of total salt intake in the Western diet. “The frequency of adding salt to foods reflects a person’s long-term salt taste preference, and it is less likely to be affected by the large day-to-day variations in sodium intake,” they explain.

The analysis included data on 501,379 participants (mean age 57 years; 54% women) in the UK Biobank who completed a questionnaire at baseline on the frequency of adding salt to foods (not including the use of salt during cooking). Overall, 55% of individuals said they never or rarely used the salt shaker, 28% sometimes did, 12% usually did, and 5% always did.

Concentrations of spot urinary sodium and estimated 24-hour sodium excretion both increased along with more-frequent use of added salt, whereas spot urinary potassium went in the other direction.

During a median follow-up of 9 years, 18,474 participants died. There was a significant trend toward a greater risk of premature death when the use of added salt was more frequent, even after accounting for various confounders. For example, those who always used extra salt were 28% more likely to die before age 75 compared with those who never/rarely did (HR 1.28; 95% CI 1.20-1.35).

Adding salt more often was associated with greater risks of cancer, CVD, and stroke mortality, but not death from coronary heart disease. That’s consistent, the investigators point out, with the results of the Salt Substitute and Stroke Study (SSaSS), which showed that use of a salt substitute reduced deaths from stroke but not from coronary disease.

The overall relationship between added salt and premature mortality was modified by fruit and vegetable intake (P = 0.02 for interaction), such that it was significantly only among individuals with a low intake of those foods. In addition, subgroup analyses suggested the association is attenuated among people with obesity or with high urinary potassium levels.

Simple, Feasible Advice

Commenting for TCTMD, Annika Rosengren, MD, PhD (Sahlgrenska University Hospital, University of Gothenburg, Sweden), who wrote an editorial accompanying the study, said a “very concrete piece of advice” that can be derived from its results is that “you shouldn’t put extra salt on your food.”

She said, however, that the larger question around salt or sodium in the diet—the optimal amount to consume on a daily basis—is a difficult and complex one because that amount probably varies across individuals.

Blanket advice from professional societies and public health bodies to consume less than about 1 tsp of salt (about 2.3 grams of sodium) per day is not optimal, Rosengren said, because most people eat about twice that amount and getting down to the recommended level would be difficult and potentially harmful for some people. Making such a big change is not sufficiently supported by randomized evidence either, she added.

Advising people to stop adding salt to their food, however, is simpler and more feasible and would likely reduce the amount of sodium consumed on a population level without causing harm, Rosengren said, noting that most of the salt ingested by individuals comes from industry-produced foods and not the salt shaker. “To cut off the top off the discretionary amount probably would keep blood pressure down and result in fewer people with cardiovascular disease, but it probably would not result in people eating too little salt.”

In her editorial, Rosengren suggests other dietary steps people can take to improve their health, saying that “to counterbalance potentially harmful effects of salt, and for many other reasons, a diet rich in fruit and vegetables should be a priority on the individual, as well as the population, level.”

At the individual level, the optimal range for salt consumption remains unclear, although “at the population level, there is no reason to be complacent about salt intake,” Rosengren writes. “There is a well-established link between salt consumption and population blood pressure levels. Public awareness about salt needs to be raised, but perhaps not in the shape of advice about target levels that are unlikely to be achieved, and which are possibly harmful in some.”