Multiple Sclerosis Symptoms and Winter Weather

The hormone melatonin naturally increases when days are shorter and could explain why multiple sclerosis symptoms often decrease in winter.

Multiple sclerosis (MS) symptoms, including weak muscles, dizziness, loss of bladder control, vision problems, and more, are caused by damage to the central nervous system. Exactly why that damage comes about in the first place isn’t known. However, evidence points to MS likely being an autoimmune process caused by genetic vulnerabilities combined with environmental factors, according to the National Institute of Neurological Diseases and Stroke. 

In fact, environmental factors may influence why MS symptoms can be so variable and wax and wane. For example, MS patients often improve in the winter months, a fact that has puzzled doctors and patients alike. But neuroscientist Francisco Quintana, PhD, of the Ann Romney Center for Neurologic Diseases at Brigham and Women’s Hospital, and colleagues at the Raul Carrea Institute for Neurological Research believe they’ve found an important clue to solve that mystery — and it offers hope for new MS treatments.

It turns out that melatonin, a naturally occurring hormone linked to regulating a person’s sleep-wake cycle, increases as days grow shorter. And this boost of melatonin in the winter may slow down or improve MS symptoms. 

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"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," said Quintana. "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."

For their study, Quintana and his research team investigated a group of 139 patients diagnosed with the relapsing and remitting type of MS. All the research subjects experienced a significant improvement in symptoms during the winter months.

Searching for an explanation to these shifts in how the MS patients felt, the researchers looked for environmental factors (such as levels of vitamin D, ultraviolet light exposure, and upper respiratory tract infections) that previous studies indicated can impact MS. 

However, melatonin was the only thing Quintana and his team found that was consistently associated with the positive changes in the research participants’ MS symptoms. Melatonin levels are known to be lower during the longer days of the spring and summer, but levels begin climbing during the shorter days of fall and winter — the same time of year when the MS patients in the study felt better.

The research team investigated this lead in the lab, too, studying the role melatonin plays on a cellular level. They tested the effects of the hormone on human cells and on a mouse model of the disease and found that melatonin affected two kinds of cells involved in the progression of MS — pathogenic T cells, that attack and destroy tissue, and regulatory T cells, which fail to regulate T cells in MS. 

“We found that melatonin has a protective effect,” said Quintana. “It dampens the immune response and helps keep the bad guys — or pathogenic T cells — at bay.”

If you have MS, Quintana warns against self-medicating with melatonin supplements. Although the hormone is available over the counter, it can have side effects, including significant drowsiness. 

“In the future, melatonin or its derivatives may be used in MS patients after appropriate clinical trials are conducted and dosage is established,” he explains. 

To that end, Quintana and colleagues are planning a pilot clinical trial to study the effects of melatonin on the immune systems of MS patients and to identify additional ways the hormone may impact MS, too. The team’s goal is to document melatonin’s effects on a molecular level and then develop targeted, safe, and non-toxic drugs with minimal side effects that can benefit MS patients.