Teenage girls' weight is 'critical' in determining their risk of developing MS as adults, a US study suggests.
Researchers found that obese teenage girls were twice as likely to develop MS as girls who were not overweight. Harvard School of Public Health researchers studied 238,371 women aged 25-55 years old and asked about their height and weight at age 18.
The researchers calculated women's BMI from these figures. The women also selected silhouettes that they thought best represented their body sizes at age five, 10 and 20.
The participants were then followed for 40 years during which time 593 developed MS.
Women who had a BMI of 30 or more at age 18 were twice as likely to have developed MS compared with women whose BMI was 18.5-20.9 at age 18.
After adjusting for body size at the age of 20, a large body size at five or 10 years old was not associated with an increased risk of MS.
A large body size at the age of 20 was associated with a 96 per cent increased risk of MS.
The researchers found no significant association between adult body mass and MS risk.
'These results suggest that weight during adolescence, rather than childhood or adulthood, is critical in determining MS risk, consistent with the body of evidence identifying adolescence as an important period in MS aetiology,' the researchers said.
They suggest that this increased risk of MS may be caused by reduced circulating vitamin D levels in obese youngsters.
Even if differences in vitamin D levels are moderate, they could have important effects if they occur at an age critical for MS development, they add.
This effect could be enhanced by a chronic, low-level inflammatory state in obese individuals, they said.