Thousands of studies have explored the effects of sodium on health. They have covered the range of medical research from broad comparisons of sodium intake and health across countries to look-back studies comparing people with heart disease or stomach cancer to those without (case-control studies), long-term follow-up studies, experiments in which one group of people consumed less sodium than another group, and laboratory studies of the impact of sodium on cells and tissues.
All this effort has yielded a broad consensus about connections between sodium and health.
Salt and the Cardiovascular System
The lion’s share of research on sodium and health has focused on high blood pressure, stroke, heart disease, and heart failure. The majority of these studies show that blood pressure rises with increasing amounts of sodium in the diet, and that sodium reduction lowers cardiovascular disease and death rates over the long term.
One way to make sense out of so much information is with a technique called meta-analysis. It takes the data from all the available studies and provides a statistical summary of the results.
Several meta-analyses have been done on studies of salt intake and blood pressure. The largest and most recent of these was conducted by a team from the University of Naples Medical School in Italy and the University of Warwick in England. They pooled the results of 13 cohort studies that included 177,025 men and women who were followed for 3.5 years to 19 years.
Over the course of the follow-up, more than 11,000 of the participants experienced a heart attack or stroke, developed another form of cardiovascular disease, or died of cardiovascular disease.
Higher salt intake was associated with a 23 percent increase in stroke and a 14 percent increase in heart disease.
You can read a summary of three key studies, all different types, that highlight the various findings on sodium and cardiovascular disease: Intersalt, DASH (Dietary Approaches to Stop Hypertension), and TOHP (Trials of Hypertension Prevention).
Salt and Cancer
Several dozen studies have explored connections between salt, sodium, or salty foods and cancer. The data from these studies show that, in general, higher intakes of salt, sodium, or salty foods is linked to an increase in stomach cancer. The World Cancer Research Fund and American Institute for Cancer Research concluded that salt, as well as salted and salty foods, are a “probable cause of stomach cancer.”
Salt and Bones
The more salt you take in, the more calcium your body flushes out in the urine. If calcium is in short supply, it can be leached out of the bones. So a diet high in sodium could have an additional unwanted effect—the bone-thinning disease known as osteoporosis.
A study in post-menopausal women showed that the loss of hip bone density over two years was related to the 24-hour urinary sodium excretion at the start of the study, and that the connection with bone loss was as strong as that for calcium intake. Other studies have shown that reducing salt intake causes a positive calcium balance, suggesting that reducing salt intake could slow the loss of calcium from bone that occurs with aging.