Potential deleterious impact of dietary salt restriction on cardiovascular risk factors

Excessive intake of dietary salt is thought to promote hypertension in Western societies, and some have recommended salt restriction for the general population. While such restriction is thought to be innocuous, few studies have examined the impact of dietary salt on cardiovascular risk factors other than blood pressure. In a randomized, placebo-controlled, doubly blinded comparison of one week periods of 20 vs. 208 mEq/d NaCl intake in 27 hypertensives and normotensives, we found that salt restriction had no significant effect on blood pressure (p = 0.45) and a generally adverse impact on risk factors for cardiovascular disease. Stringent, short-term dietary salt restriction caused increases in total and low-density lipoprotein cholesterol that were of borderline significance (p = 0.07). These lipid effects probably resulted from plasma volume contraction, as they were coincident with significant rises in hemoglobin (p = 0.01), hematocrit (p less than 0.001), total protein (p less than 0.01) and albumin (p = 0.01); such changes may act together to increase whole-blood viscosity. In addition, plasma norepinephrine (p = 0.02), fasting plasma insulin (p = 0.02) and glucose-to-insulin ratio (p = 0.01) increased during salt restriction. The potentially adverse impact of dietary salt restriction on the risk factor profile for cardiovascular disease suggests that further studies are necessary before a reduction in dietary salt intake can be prescribed for the general population.