Blood Sodium Level Does Not Affect Blood Pressure

Led by Dr. Rodrigo M. Lago of the Framingham Heart Study, Framingham, Mass., the researchers analyzed the relationship between serum sodium levels and blood pressure in nearly 2,200 subjects from a long-term study of cardiovascular disease risk factors. At the start of the study, none of the subjects had high blood pressure (hypertension). Each subject's blood pressure was defined as optimal, normal, or high-normal.

Serum sodium level increased with age. In addition, subjects with higher sodium levels had a higher rate of diabetes and a higher creatinine level (suggesting decreased kidney function).

Sodium Level Does Not Predict Blood Pressure, Now or in the Future
However, there was no relationship between the serum sodium level and blood pressure. Sodium was also unrelated to sex and body weight.

During four years' follow-up, blood pressure increased by at least one stage (for example, from normal to high-normal) in 37 percent of subjects. This included the development of high blood pressure in 15 percent of subjects.

However, the risk of increasing blood pressure was unrelated to serum sodium level. In fact, subjects in the highest serum sodium category were at lower risk of developing high blood pressure.

There is a well-known link between high levels of sodium in the diet and the risk of high blood pressure. More recent studies have suggested that higher levels of sodium on routine blood tests might be linked to increased blood pressure. These studies raised the interesting possibility that variations in serum sodium level might explain some of the variation in blood pressure in the population. If so, then measuring serum sodium might provide a way of predicting a person's future risk of high blood pressure.

Watching Salt in the Diet Is Still Important
However, the new results show no significant link between serum sodium level and blood pressure. People with higher serum sodium levels do not have higher blood pressure, and are not more likely to develop hypertension in the future. The findings may reflect the many different factors contributing to differences in blood pressure between individuals.

Meanwhile, Dr. Lago and colleagues emphasize that their results do not negate the “critical role” of salt in the diet. More likely, they reflect the body's “tight regulation of serum sodium within a narrow physiologic range.” In other words, since the range of normal sodium levels is so small, variations in serum sodium aren't a good indicator of hypertension risk.

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