Researchers examined data on more than 238,000 women who participated in the Nurses' Health Study, which began in 1976, and the Nurses' Health Study II, which began in 1989. Participants self-reported what their height and weight were at the start of the study and what they had been at age 18. They also chose silhouettes to describe their body shapes when they were ages 5, 10, and 20 years old. Participants were between 25 and 55 years old when the studies began.
The study tracked participants for more than 40 years from both groups combined. During that time there were 593 cases of MS.
The women's body mass index (BMI) at age 18 and the way they described their overall body shape at age 20 were linked to the likelihood of developing MS in adulthood. Women who had a BMI of 30 or larger (considered obese) at age 18 had more than twice the risk of women with a BMI between 18.5 and 20.9. Normal weight BMI is 18.5 to 24.9.
The results were the same after accounting for factors such as smoking status, age, and ethnicity.
There also was a link between the women who chose a larger silhouette to describe themselves at age 20 and an increased risk for MS.
Being obese as determined by the BMI at the start of each study was not linked to likelihood of MS. Body silhouette self-selected at age 5 also wasn't linked to risk for developing MS later in adulthood.
"Our results suggest that weight during adolescence, rather than childhood or adulthood, is critical in determining the risk of MS," study researcher Kassandra Munger, ScD, of Harvard School of Public Health, says in a news release. "Teaching and practicing obesity prevention from the start, but especially during teenage years, may be an important step in reducing the risk of MS later in life for women."