A higher intake of dietary sodium, most often in the form of salt, does not increase the risk of developing multiple sclerosis (MS), Norwegian researchers concluded after analyzing data from more than 175,000 women.
Their findings counter earlier evidence from experimental studies in cells and MS mouse models that suggested sodium may be a disease trigger.
The report, “No association between dietary sodium intake and the risk of multiple sclerosis,” appeared in the journal Neurology.
To examine the link between sodium and MS, researchers at Norway’s University of Bergen turned to two large U.S. population studies — the Nurses’ Health Study and the Nurses’ Health Study II — running between 1984 and 2007.
Women included in the studies completed questionnaires every other year. Dietary sodium intake was evaluated by a validated food frequency questionnaire given every four years. Researchers extracted data on sodium amounts by assessing the intake of common salt sources such as sandwiches, pizza, cheese, snacks, pasta or meat dishes. They also included non-salt sodium sources like glutamate and bicarbonate.
Of the participants, 479 developed MS during the studies. While researchers did observe a link between higher sodium intake and increased body mass index or heavier smoking, they found no association between sodium intake and the risk of developing MS.
When they divided participants into those consuming the most and least sodium, they could not find any links to MS. They repeated this analysis separately in smokers and non-smokers, and again failed to find an association between sodium and MS.
Researchers said they might have reached a different result than did earlier animal studies, because animals were fed much higher doses of sodium than were people. Even those on high-salt diets do not reach levels as high as those in the animal studies, they said.
But just as the present study, the only earlier study in humans found no link between sodium and MS.
The team admits that its study was limited by several factors, including the fact that only women participated. Even so, while studies in men would be needed to confirm the results, they argue that the scientific evidence is lacking to support a scenario in which men’s sodium intake would raise their risk of MS.