Young men, ages 16 to 20, with a higher the body mass index (BMI) are at greater their risk of being diagnosed with multiple sclerosis (MS) later in life, regardless of physical fitness, according to a Swedish study.
Risk rose across “the entire BMI range,” its researchers reported, starting with normal weight compared to underweight.
The study, “Higher body mass index at ages 16 to 20 years is associated with increased risk of a multiple sclerosis diagnosis in subsequent adulthood among men,” was published in the Multiple Sclerosis Journal.
While the underlying cause of MS is unknown, both genetic and environmental factors are thought to play a role in disease onset. For men, a suggested environmental factor is higher BMI, particularly obesity, prior to adulthood.
A recent comprehensive review found mixed evidence to support this claim, leading researchers at Örebro University to more closely investigate the relationship between BMI and MS diagnosis in younger men.
Their study included data regarding each individual’s specific BMI, as opposed to grouping people by weight categories: underweight, normal weight, overweight, or obese.
Data covered 744,548 males born between 1970 and 1992, and registered in the Swedish Military Conscription Register between the ages of 16 and 20. Of these people, 952 (0.13%) were later diagnosed with MS; their average age at diagnosis was 31.2.
Researchers were able to show a linear relationship between BMI earlier in life and the likelihood of an MS diagnosis in adulthood. In fact, for every additional point on the BMI scale, which typically ranges from 15 to 35, the risk of a subsequent MS diagnosis rose by 3.4%.
Among those who went to develop MS, 40 were underweight (BMI of 15 to 18.5), 738 were of normal weight (18.5 to 25), 135 were overweight (25 to 30), and 39 were obese (BMI above 30). When accounting for age at the time of BMI measurement and their parent’s socioeconomic status, males who were underweight were 35.7% less likely to be diagnosed with MS than were those of normal weight before adulthood.
Overweight individuals were 21.8% more likely, and obese individuals were 39.6% more likely to be diagnosed with MS as adults.
After further adjusting for an individual’s level of physical fitness, the linear relationship between BMI and MS diagnosis was still significant, as was the lower risk for underweight individuals. The risk increase for overweight and obese individuals, however, was no longer significant.
“It is possible that early symptoms of MS such as fatigue, poor coordination, and pain affect BMI, but the association of BMI with MS risk seems to be independent of physical fitness as the association persisted over the lower range of BMI after adjustment for physical fitness,” they wrote.
A higher BMI between ages 16 and 20 was seen to correlate with an increased risk of MS diagnosis later in life.
“In conclusion, higher BMI at ages of 16–20 years was associated with higher subsequent MS risk among men across the entire BMI range (a dose-dependent effect not only limited to overweight or obesity) although with modest effect size,” the researchers wrote.
They noted as a strength of their study that data came from objective measures of BMI, as opposed to a self-reported measures.
They also noted some shortcomings, including that data on other risk factors, such as smoking, vitamin D, or genetics, were not available, nor was information on MS symptoms in individuals before age 20.
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