Darkness and light may help prevent multiple sclerosis or fend off its symptoms.
People who genetically produce less vitamin D, a compound normally boosted by sun exposure, have a greater risk of multiple sclerosis, researchers find. But the hormone melatonin, which the body produces in response to darkness, may reduce flare-ups for people who have the disease, another team of scientists reports.
The studies may help researchers better understand and treat multiple sclerosis, a disease of the nervous system. It causes symptoms including muscle weakness, pain and vision loss in over 2 million people worldwide.
Previous studies linked lower vitamin D levels to higher multiple sclerosis risk, but it was unclear whether this relationship was a coincidence. In work appearing August 25 in PLOS Medicine, scientists examined genetic data from thousands of Europeans and found that three genetic changes known to reduce vitamin D levels were associated with increased multiple sclerosis risk.
These findings suggest that individuals with a higher risk of developing the disease, such as immediate family members of multiple sclerosis patients, should take steps to ensure they have sufficient levels of vitamin D, says study coauthor Brent Richards, a genetic epidemiologist at McGill University in Montreal. People can raise vitamin D levels to normal by taking an oral supplement.
Scientists have also observed a seasonal paradox in the relationship between vitamin D and multiple sclerosis. In the sunnier spring and summer, when vitamin D levels should be higher, patients with multiple sclerosis symptoms tend to experience more symptoms. In a study in the Sept. 10 Cell, researchers found that over five years, 139 observed patients had 32 percent fewer relapses in fall and winter. Patients also produced more melatonin, a sleep-inducing hormone that increases in response to daily and seasonal darkness, in the fall and winter.
Patients with lower levels of melatonin — as measured by the amount of a melatonin by-product in their urine — had more multiple sclerosis relapses, the researchers found. In mice, daily melatonin treatments reduced the symptoms of an immune condition that mimics a multiple sclerosis flare-up. And in mice, mouse cells and human cells, melatonin boosted production of anti-inflammatory immune cells, while suppressing the development of inflammatory immune cells believed to contribute to multiple sclerosis symptoms.
It’s probably not ideal to use melatonin as a drug for multiple sclerosis because the hormone could have side effects, says coauthor Francisco Quintana, an immunologist at Harvard Medical School and Brigham and Women’s Hospital in Boston. Instead, the study’s results could inform future therapies that mimic melatonin’s anti-inflammatory mechanisms, he says.
While melatonin seems to be primarily responsible for seasonal relapses, vitamin D also clearly plays a role in multiple sclerosis, Quintana says.
Both studies help scientists understand an incredibly complex condition, says immunologist Daniel Altmann of Imperial College London. Researchers can now further investigate exactly how vitamin D and melatonin operate in multiple sclerosis, he says. “It’s phenomenally exciting.”