Nov. 9, 2011 -- Everyone knows that too much salt is bad for you, right? Well, according to new research, not everyone is convinced.
Reducing dietary sodium (salt) helps lower blood pressure a little, but it also may increase levels of some hormones and unhealthy blood fats, a new review of studies shows.
Researchers say that means cutting back on sodium may not have a substantial health benefit.
But critics say the review draws faulty conclusions because it relies on too many small, short-term studies. They say the weight of research evidence shows clear health benefits when people cut back on sodium.
The review is an analysis of data from more than 167 studies of people with normal or high blood pressure who were randomly assigned to eat either high- or low-sodium diets.
It found that eating less than 2,800 milligrams of sodium a day helped lower blood pressure. But the reductions were small -- an average of 1% for people who had normal blood pressure to begin with and 3.5% for people with high blood pressure.
But cutting back on salt appeared to have other effects, too.
People on lower-sodium diets had an average 2.5% increase in cholesterol and a 7% increase in bad blood fats called triglycerides compared to people who were eating more than 3,450 milligrams of sodium -- an amount that's close to what the CDC says the average American eats every day.
Higher cholesterol and triglyceride levels are thought to be associated with an increased risk of heart disease, which can lead to heart attacks and strokes.
Researchers say it's not clear why cutting back on sodium may affect blood fats.
Lower-sodium diets also boosted levels of the hormones renin and aldosterone, which can raise blood pressure. Researchers say that may be one reason that slashing salt from the diet has only modest effects on blood pressure.
"The theory that you can reduce the risk of cardiovascular disease by reducing salt intake and thereby blood pressure is tempting. But our study shows that the effect of reduced salt intake on blood pressure in healthy persons is only 1%," says study researcher Niels A. Graudal, MD, DrMedSci, in an email to WebMD.
"Furthermore, reduced salt intake leads to an increase in lipids [blood fats], which is bigger than the reducing effect on blood pressure. Therefore it is likely that reduced salt intake does not have a beneficial effect. On the contrary the net effect may be harmful," says Graudal, who is a senior consultant in the departments of rheumatology and internal medicine at Copenhagen University Hospital in Denmark.
The study is published in the American Journal of Hypertension.