Very obese children and teens may be at risk for multiple sclerosis, a new study suggests.

In the study, very obese girls (those who had a body mass index (BMI) of 35 or higher) were nearly four times more likely to be diagnosed with multiple sclerosis (MS) within the study period, compared with girls who were normal weight. The link was strongest among teenagers.

No link between obesity and multiple sclerosis was found for girls in other weight classes, or for boys.

In people with MS, the immune system attacks the nerve cells of the brain and spinal cord, producing symptoms such as numbness, loss of balance, weakness and tremors. MS is rare in children — about one to two kids out of every 100,000 will develop the condition. Symptoms are similar in children and adults, although youngsters may also experience symptoms not typical of MS, such as seizures or lethargy, according to the National Multiple Sclerosis Society.

The findings suggest that, as the prevalence of childhood obesity increases, so will cases of multiple sclerosis, said study researcher Dr. Annette Langer-Gould, of Kaiser Permanente Southern California Department of Research & Evaluation in Pasadena, Calif.

“Our study suggests that parents or caregivers of obese girls and teenagers should pay attention to symptoms such as tingling and numbness or limb weakness, and bring them to a doctor's attention,” said Langer-Gould.

However, the study only found an association, and cannot prove that obesity causes multiple sclerosis. It could be that an aspect of the condition itself — such as having trouble exercising before the condition is diagnosed — predisposes youngsters to obesity. But if this were the case, researchers would expect to see the same link in girls and boys, which the study did not find, Langer-Gould said.

The researchers analyzed information from 75 children and teens ages 2 to 18 who were diagnosed with pediatric MS, and compared them with more than 913,000 children and teens who did not have MS. For those with MS, BMI was measured before the condition was diagnosed.

Obesity is known to increase inflammation in the body, which may be involved in the development of MS, Langer-Gould said. Estrogen, a female hormone, also increases inflammation, and together with other inflammatory factors released from fat cells, could accelerate the development of MS, Langer-Gould said. The involvement of estrogen might explain why the link was only seen in girls.

“The authors certainly have opened the door to an interesting association,” said Dr. Michael Duchowny, a pediatric neurologist and director of academic affairs at Miami Children's Hospital Research Institute, who was not involved in the study. “These findings need to be repeated, expanded and clarified further” with additional research, including studies that test the estrogen hypothesis, Duchowny said.

Previous studies in adults have suggested that obesity, or related factors, such as levels of appetite hormones, play a role in the development of MS, said Dr. Steven Mandel,  a neurologist at Lenox Hill Hospital in New York City.

“It doesn't mean that if you're obese or overweight ,you're going to develop MS,” but rather, that a link between the two conditions exists, Mandel said. The findings may be another reason to bring childhood obesity under control, he said.

Although preliminary, some saw the findings as hopeful.

“We're beginning to accumulate a good deal of information about some of the environmental factors that may play a role in MS, and environmental factors that are possible to be modified,” such as smoking and obesity, said Dr. Nicholas LaRocca, vice president of health care delivery at the National Multiple Sclerosis Society. “That’s a very exciting possibility,” LaRocca said.

The study will be published today (Jan. 30) in the journal Neurology.

Pass it on: Childhood obesity is linked to an increased risk of MS.

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