In the current Neurology study, high blood levels of vitamin D were defined as readings of 75 nanomoles per liter (nmol/L) or above. The Institute of Medicine, a non-profit group affiliated with the U.S. National Academy of Sciences, has said people should aim for blood levels of 50 nmol/L, which can be achieved with vitamin D supplements of 600 international units (IU) per day, or 800 IU for those older than 70.
Salzer noted that scientists don't yet know if one source of vitamin D -- whether sunlight, diet or supplements -- affects blood levels more than another, calling it "the $10,000 question."
"Sunlight, and its UVB radiation, has immune-modulating properties apart from generating vitamin D, and these effects might actually influence MS risk as well," Salzer said. "Given the current knowledge, however, I'd say that the case for vitamin D is stronger than for sunlight in itself."
Dr. Karen Blitz-Shabbir, director of the Multiple Sclerosis Center at Cushing Neuroscience Institute in Manhasset, N.Y., said she recommends blood tests measuring vitamin D levels for all her patients and would for the general population as well. She also recommends vitamin D supplements for all, noting that the much-researched vitamin has also been shown to hinder the systemic inflammation that can contribute to other serious conditions such as heart disease and cancer.
"Everything we see points to the value of vitamin D in MS," she said. "This study makes absolute perfect sense."
While the study found an association between lower vitamin D levels in pregnancy and MS risk, it did not prove a cause-and-effect relationship.
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