By Maureen Salamon
THURSDAY, Sept. 10, 2015 (HealthDay News) -- Higher levels of the hormone melatonin are linked to a lower incidence of multiple sclerosis (MS) flare-ups during the darker months of fall and winter, new research suggests.
American and Argentinian scientists also found that treating mice with melatonin could improve symptoms of the disease, which can be progressive and often disabling.
But study authors stressed that the findings don't mean patients with MS should self-dose high levels of melatonin, available in over-the-counter supplements often used to promote sleep. Rather, the research may spur more targeted approaches to MS without causing unwanted or dangerous drowsiness, they said.
"MS is an immune-mediated disease where the immune system actually attacks the central nervous system," said study author Francisco Quintana, a researcher from Brigham and Women's Hospital in Boston.
"Melatonin controls the balance between pro-inflammatory and anti-inflammatory activities in the immune response," said Quintana, who is also an associate professor of neurology at Harvard Medical School. "But the word of caution is, we're not saying MS patients should run out and start buying tons of melatonin."
The study is published Sept. 10 in the journal Cell.
About 2.3 million people worldwide are estimated to have MS, with the average American standing a one in 750 chance of developing the disease, according to the National MS Society. Symptoms can range from fatigue and vision problems to paralysis and thinking difficulties.
The disorder is believed to be triggered by immune cells called T-cells that destroy the material known as the myelin sheath that surrounds and protects nerve cells.
Melatonin, the so-called "darkness hormone" produced in the brain, regulates sleep-wake cycles and immune response. Levels typically are higher in people during the shorter days of fall and winter, and lower during the longer days of spring and summer.
Quintana and his colleagues studied a group of 139 patients with relapsing-remitting MS, a course of disease characterized by flare-ups and periods of stability. They found that participants experienced a 32 percent reduction in relapses during fall and winter compared to spring and summer.
The researchers also gave daily injections of melatonin to mice with an autoimmune disease mimicking several key features of MS. The melatonin improved symptoms in the mice and reduced levels of harmful T-cells known as Th17 cells, restoring a healthy balance of T-cells in the brain, spinal cord and organs involved in immune response, the researchers said.
Scientists note, however, that research with animals often fails to produce similar results in humans.
The new research suggests a stronger basis for melatonin's role in controlling seasonal MS flare-ups compared to vitamin D, another environmental factor that could play a role in MS relapses, Quintana said.
Vitamin D is thought to help cut the frequency of MS flare-ups in spring and summer -- when natural melatonin levels are lower -- due to its anti-inflammatory effects. But "it looks that melatonin has the better association," Quintana said. "The two of them [melatonin and vitamin D] contribute to control disease activity, but specifically with regards to seasonal changes, melatonin plays a stronger role than vitamin D in MS."
Since seasonal flare-ups are also common with other inflammatory conditions such as lupus and rheumatoid arthritis, Quintana and other MS experts believe the new research may one day have broader impact on treatment for these autoimmune problems.
Dr. R. Glenn Smith, a neurologist at Houston Methodist Hospital in Texas, called the new study "surprising and potentially exciting, but there's a lot of research that's gone forward in the past that's led to this."
"It does describe [how] melatonin seems to be having an important regulatory role in the overall health and responsiveness of the immune system," Smith said. "These changes and how they affect the immune system are going to be important more than just for MS."
Clinical trials testing the concept further in humans are in the planning stages, Quintana said.
He and Smith agreed that MS patients should not try to self-medicate with high amounts of melatonin supplements in an effort to curb their disease because much more research is still needed.
"Melatonin might be good for sleeping better, but we need something more targeted to act on specific receptors ... for a stronger anti-inflammatory effect without the side effects you wouldn't want," Quintana said. "You wouldn't want to be drowsy throughout the day."