Obese girls are at greater risk of developing multiple sclerosis or MS-like illness, according to a new study published Wednesday in the online journal Neurology.

Researchers looked at body mass index (BMI) data from more than 900,000 children from the Kaiser Permanente Southern California Children's health study. Seventy-five of those children and adolescents between the ages of 2 and 18 were diagnosed with pediatric MS. More than 50% of them were overweight or obese, and the majority were girls.

According to the study, the MS risk was more than one and a half times higher for overweight girls, almost two times higher in moderately obese girls and almost four times higher in extremely obese girls.

"Over the last 30 years, childhood obesity has tripled," said study author Dr. Annette Langer-Gould, a neurologist and regional MS expert for Kaiser Permanente in Southern California. "In our study, the risk of pediatric MS was highest among moderately and extremely obese teenage girls, suggesting that the rate of pediatric MS cases is likely to increase as the childhood obesity epidemic continues."

MS is a chronic, debilitating disease that attacks the central nervous system. "Some patients do very well and have minimal to no disability even 20 years later," Langer-Gould said, "While other patients do poorly and can be wheelchair bound in 5 years. It's a huge spectrum."

Dr. Tanuja Chitnis is a neurologist and pediatric MS specialist at Massachusetts General Hospital for Children with 50 MS publications to her credit. She says 10 years ago MS was not recognized as a disease that occurred in children, but today evidence is mounting that obesity is a risk factor for MS in kids, particularly adolescent girls.

"This is one more piece of evidence, but really in order to make a definitive link, you need at least five or six studies showing the same thing," she says. "You need to have an underlying biological reason, which still has not been worked out and you need to show that blocking or interfering with the biological mechanism can prevent the disease."

"The overall message is that there are an increasing number of diseases associated with obesity and particularly early obesity and that it's an important risk factor to try to mitigate. It is something you can do something about," Chitnis says.

According to the Centers for Disease Control and Prevention, over the last 30 years childhood obesity has doubled in children and tripled in teenagers. In 2010, more than a third of all children and teens were overweight or obese.

At Children's Hospital of Alabama, pediatric neurologist Dr. Jayne Ness has seen more than 100 pediatric MS patients, predominantly girls, whose average age at onset is 13. Ness told CNN she has noticed a rise in obesity in their MS patients, kids who at the time of diagnosis are obese.

"Does this mean that obesity is a risk factor for MS? We don't know yet," Ness said. "It's one more piece that helps us potentially better understand some of the underlying triggers of pediatric MS and may help us understand MS in general."

Langer-Gould says that while pediatric MS is very rare - only 1.6 per 100,000 children - there are red flags parents should look out for. "Constant numbness or tingling from the waist down or numbness, pins and needles sensations in the chest, abdomen or back that last for 24 hours."

Those children should be evaluated by a neurologist. Other symptoms to have checked out are collapsing weakness in the legs after modest exertion, and pain and loss of vision in one eye.

The National MS Society estimates about 10,000 children in the United States have the disease and another 10 to 15,000 have had at least one MS-like symptom. An estimated 5% of all MS cases worldwide are childhood or adolescent onset.