By Amy Norton
And once obese children are diagnosed, they tend to have a poorer response to their initial treatment than average-weight kids do.
Multiple sclerosis (MS) is a neurological disorder caused by a misguided immune system attack on the body's myelin -- the protective sheath around nerve fibers in the spine and brain. Depending on where the damage occurs, symptoms include vision problems, muscle weakness, numbness, and difficulty with balance and coordination.
Although the disease mainly affects adults, it can strike early in life. In the United States, an estimated 8,000 to 10,000 children and teenagers have MS, according to the National Multiple Sclerosis Society.
A number of studies have found a connection between obesity and higher MS risk in adults, though the reasons why are unclear.
The new study is the largest to link obesity and MS in children -- and the first to suggest it might affect their treatment response, said senior researcher Dr. Peter Huppke. But the study did not prove that obesity causes MS risk to rise.
The precise cause of MS in children is unknown, noted Huppke, who is based at the University Medical Center Gottingen, in Germany. But, he said, it's thought to be a combination of genetic vulnerability and various environmental factors.
In theory, there are several reasons obesity might be one risk factor, according to Huppke. Obesity causes body-wide inflammation, and may alter vitamin D levels in the body or the bacterial composition in the gut; research suggests those mechanisms, in turn, are involved in MS.
Those are plausible explanations, agreed Kathleen Costello, associate vice president of health care access for the National MS Society.
Costello said the new findings build on evidence that obesity is a risk factor for MS. "That's an important observation," she said, "because it's a risk factor that is modifiable."
As for the finding on obesity and kids' medication responses, Costello called it "interesting" -- though the implications are unclear right now.
"It's certainly something that needs further research," she said.
The findings, published online July 15 in JAMA Neurology, are based on medical records from 453 children diagnosed with MS at one medical center. Huppke's team compared them with nearly 15,000 German children who were involved in a separate health study.
Overall, obese children had twice the risk of being diagnosed with MS, with the findings being consistent in girls and boys. Overweight kids, meanwhile, were 37% more likely to develop MS than their average-weight peers.
Is it possible that early MS symptoms could have caused some kids to gain excess weight? Huppke said he thinks it's "highly unlikely." One reason is, the children did not have substantial weight gain after their diagnosis.
When it came to medication, obese kids were less likely to do well on their first therapy. They had a higher rate of symptom relapses on the standard medications interferon-beta and glatiramer acetate. And they were more likely to need a "second-line" therapy -- 57% did, versus 39% of normal-weight kids.
Again, it's not clear why. But body fat levels are known to affect absorption of some non-MS medications.
According to Huppke, that suggests that weight loss might improve obese kids' response to MS drugs. It also raises the question of whether it would be helpful to adjust children's medication doses according to weight, he said.