(Reuters) - Obese children, adolescent girls in particular, are more likely to be diagnosed with multiple sclerosis (MS) than normal-weight youth - with extreme obesity tied to a three- to four-fold higher risk of MS.
The study didn't prove that carrying around some extra eight in childhood causes MS, a neurological disease in which the protective coating around nerve fibers breaks down, slowing signals traveling between the brain and the body, said researchers whose work appeared in the journal Neurology.
But it does suggest that rising levels of obesity in young people could mean more MS diagnoses than in the past, according to lead study author Annette Langer-Gould from Kaiser Permanente of Southern California and her colleagues.
For the study, Langer-Gould and her colleagues compared the heights and weights of 75 young people with pediatric MS and its possible precursor, a condition called clinically isolated syndrome (CIS), and more than 900,000 without the disease.
"Our findings suggest the childhood obesity epidemic is likely to lead to increased morbidity from MS/CIS, particularly in adolescent girls," Langer-Gould and her colleagues wrote.
Just over half of the children and teens with MS were overweight or obese, compared to 37 percent of other youth.
Being overweight or moderately obese was tied to a slightly higher chance of MS in adolescent girls, but the results were based on a small number of cases and could have been due to chance. Extreme obesity, on the other hand, was linked more clearly with a three- to four-fold higher risk of MS.
A 12-year-old girl who stands 1.52 meters (5 feet) tall and weighs 51 kilograms (112 pounds) is considered overweight and extremely obese at over 70 kg (155 pounds).
There was no clear pattern between boys' weights and how likely they were to be diagnosed with MS, Langer-Gould's team found.
"Obesity is increasing the risk of so many different kinds of diseases," said Kassandra Munger, who studies MS at the Harvard School of Public Health in Boston but was not involved in the new study.
"This current study now adds to the evidence that it's also dangerous and increases the risk of neurological diseases, such as multiple sclerosis."
Roughly 400,000 people in the United States have MS, usually diagnosed in adulthood. Just one or two out of every 100,000 children is diagnosed with pediatric MS, Langer-Gould said.
Based on limited evidence about any effects of weight, she said she was "actually surprised" her team found any link with MS risk.
"It's not something we think of as a risk factor for multiple sclerosis," she told Reuters Health.
According to Munger, there are a number of possible explanations for why heavy people could be at increased risk, including their vitamin levels and the greater amounts of chemicals - such as inflammation-inducing signaling molecules - secreted by their fat cells.
"It's not easy to tease those out," Munger told Reuters Health. "From a biological perspective, we don't know what the link is between obesity and MS."
Langer-Gould and her colleagues are continuing to track children in their study over time and are also working on another project to see if adults' weight affects their chance of developing MS. SOURCE: http://.bit.ly/IUcacJ
(Reporting from New York by Genevra Pittman at Reuters Health; editing by Elaine Lies)