Why Do Multiple Sclerosis Symptoms Improve in the Winter?

Doctors and patients have wondered why symptoms of MS tend to get better in the winter and why they worsen in the summer. A group of researchers, led by Francisco Quintana, associate professor at the Ann Romney Center for Neurologic Diseases at BWH, first examined the possibility of several environmental factors at play and based on such, conducted preclinical models of MS.

The research team found that melatonin, a hormone used to regulate an individual’s sleep cycle, may impact MS disease activity. “We know that for multiple sclerosis and most autoimmune diseases, both genetic and environmental factors play an important role, but in the last decade or so, most research has focused only on the genetic side of the equation. But we wanted to see what environmental factors would reveal to us about this disease. We knew that MS disease activity changed with the seasons. What we've uncovered offers an explanation for why that is the case” said co-corresponding author Quintana.

Melatonin levels respond to day duration

Working closely with other colleagues, the team found that during the fall and winter, the group of 139 patients with relapsing remitting MS experienced major improvements in symptoms by 32%. They went on to explore several environmental factors, such as vitamin D levels, upper respiratory tract infections and more, but found that the greatest impact in the severity of MS systems was seen to be associated with melatonin. The team uncovered that melatonin levels responded to day duration - since the days are longer in the summer and spring, the melatonin levels were lower and since the days are shorter in the fall and winter, the melatonin levels were higher. They went on to test their theory in human cells and in a mouse model so that they could see the effects of melatonin on particular forms of cells. They found that the number of protective T-cells in the mice increased greatly and the number of harmful cell groups decreased. “We found that melatonin has a protective effect. It dampens the immune response and helps keep the bad guys -- or pathogenic T cells -- at bay” said Quintana.

While melatonin is available as an over the counter dietary supplement, it presents some potentially dangerous side effects, such as extreme drowsiness. The team’s main objective is to divide the hormone’s molecular mechanisms in order to develop more targeted, non-toxic medications that are safe for use and present the least side effects. “In the future, melatonin or its derivatives may be used in MS patients after appropriate clinical trials are conducted and dosage is established. However, extreme caution should be exercised: our data do not show that melatonin or its analogs are effective in treating MS” said Quintana. 

Read on to learn more about the possible connections between treatment and MS symptom severity.