For decades, experts have been recommending that Americans cut down on their salt consumption to reduce their risk of heart attack and stroke. According to a new study, however, while reducing dietary salt does lower blood pressure, it may also lead to a slight boost in cholesterol, a separate risk factor for heart disease.
Danish researchers report in the American Journal of Hypertension that reducing sodium consumption led to a 1% drop in blood pressure in people who had normal pressure readings, and a 3.5% drop in those with hypertension. But other changes may offset those benefits: people who cut dietary salt also saw a 2.5% increase in cholesterol levels and a 7% boost in triglycerides. Like high blood pressure, elevated levels of cholesterol and triglycerides are risk factors for heart disease. Excessive triglycerides can also contribute to diabetes.
The findings were the result of a meta-analysis of 167 previously published studies involving participants with either normal and high blood pressure who were randomly assigned to low- or high-sodium diets. The studies then measured a number of different metabolic factors, including blood pressure, lipid levels and levels of an enzyme called renin, which is released by the kidneys when the body’s sodium levels fall too low, and aldosterone, a hormone that helps the kidneys to reabsorb sodium and water to raise blood pressure. Reductions in salt intake also increased these hormones.
As the study’s lead author Neil Gradual, at Copenhagen University Hospital, told Health.com: “We know that a decrease in blood pressure would probably improve or decrease the risk of cardiovascular death but, on the other hand, an increase in [cholesterol] would increase the risk. … It’s likely that these two antagonistic effects will out-balance each other, so there will be no net effect of sodium reduction on people with normal blood pressure.”
The current study isn’t the first to question the prevailing advice about lowering sodium intake to protect the heart. In reports we described here and here, researchers found that cutting back on salt did not affect a person’s risk of dying from heart-related events. “In my opinion, the recommendations [to lower sodium] should never have been there, because there’s not enough science to make [them],” Gradual told MSNBC.com.
Still, given the new study’s limitations, experts say the findings don’t give people license to eat as much salt as they want. For one thing, the studies included in the analysis generally observed participants for only a short period of time (usually less than a month), which isn’t enough time for the body to adapt fully to changes in diet. Plus, much of the slight rise in cholesterol levels did not involve LDL, or “bad,” cholesterol, the type most responsible for building up in artery walls and contributing to heart disease.
On average, participants included in the study ate 3,358 mg of sodium a day — roughly what the average American consumes — and those with hypertension consumed 2,162 mg a day. U.S. health officials recommend that adults get no more than 2,300 mg of sodium daily, with a limit of 1,500 mg for certain risk groups including those with high blood pressure, people over 50 and African Americans.
“We eat a lot of sodium — way too much — and I don’t think it’s going to hurt anybody to lower sodium in the current American diet,” Penny Kris-Etherton, a spokesperson for the American Heart Association and professor of nutrition at Pennsylvania State University, told Health.com
While some data suggest that blanket recommendations to reduce salt intake may not be necessary, especially for people with normal blood pressure who don’t overconsume sodium, cutting intake can still have a beneficial effect on blood pressure, albeit a small one, as the current study shows. So the American Heart Association and other health groups continue to advise people to keep sodium levels down, while acknowledging that salt’s effect on the body is still something of a black box.