WEDNESDAY, March 20, 2019 (HealthDay News) -- Research has suggested that kids who enter puberty early appear to face an increased risk of developing multiple sclerosis (MS) as adults.
But a new study asserts that it's actually the excess weight these kids carry around that might raise their odds for MS.
"Although we did see that people who enter puberty at an earlier age were more likely to develop MS, once we factor into their body weight, the results are no longer significant," said lead researcher Dr. Adil Harroud, a neurologist with the McGill University Health Center in Montreal. "What seems to be the main driver is not the age of puberty, but rather the individual's body weight throughout their life."
Multiple sclerosis is a debilitating autoimmune disorder in which the immune system starts attacking nerve fibers throughout the brain and spinal cord, disrupting the communication between brain and body.
Previous studies have implicated early puberty as a risk factor for MS, particularly among women, researchers said.
However, excess weight can contribute to early puberty in girls, Harroud said, and his team wondered whether those added pounds might be the real culprit here.
To sort this out, the researchers evaluated genetic data on more than 329,000 women to identify 372 genetic variants strongly associated with early age at puberty.
They then looked at another genetic study that included nearly 15,000 people with MS, and compared them with more than 26,700 healthy people, to examine whether puberty-related genes influenced risk of the nerve disease.
A one-year increase in genetically predicted age at puberty decreased a person's odds of developing MS by about 8 percent, the researchers found.
But factoring in the person's body mass index (BMI) erased the link. BMI is a measure of body fat based on weight in relation to height.
There are a couple of theoretical ways that excess weight could increase MS risk, although nothing has been proven, Harroud said.
"We know that people who have more body fat tend to have lower circulating vitamin D levels," which has been linked to MS, Harroud said.
Extra fat also increases inflammation in the body, which might spur on autoimmune disorders like MS, he added.
The findings were published March 20 in the journal Neurology.
This study is important because "it shows us there may be a modifiable risk factor here," said Nicholas LaRocca, vice president of health care delivery and policy research at the National Multiple Sclerosis Society.
"It's probably not possible to modify when puberty occurs, but obviously it is possible to modify body mass index," said LaRocca, who wasn't involved with the study.
People in families with a genetic risk of MS might want to keep a close eye on their weight, although further study is needed to shore up these findings, he added.
"If you're already in a high-risk part of the population, that would be a stronger motivation to try to deal with BMI," LaRocca said.
This is particularly true of girls and women, since much more evidence links their weight to increased MS risk, he said.
Two to three times more women than men are diagnosed with MS, according to the society.
The insidious thing is that MS typically doesn't develop until a person is in their 20s or 30s, Harroud pointed out. Teenage or childhood obesity could cause a complication that doesn't arrive until years or decades later.
The National Multiple Sclerosis Society has more about multiple sclerosis.