Birth weight and the risk of overweight in young men born at term.

OBJECTIVE

The aim of this birth cohort study was to determine the relationship between birth weight and the risk of overweight in young adulthood.

METHODS

Data from the Medical Birth Registry of Norway were linked with register data from the National Conscript Service. This study used data on the 348,800 males who were born at term in single births in Norway during 1967 to 1984, and who were examined at the mandatory military conscription (98% were examined the year they turned 18 or 19 years of age). Sibling comparisons were conducted in the 11,865 sibships of two or more full brothers in which at least one brother was overweight (body mass index ≥25.0 kg/m(2) ) and at least one brother was not overweight.

RESULTS

When all the men in the study population were compared with each other there was a "J"-shaped association between birth weight and the adjusted odds of overweight. When the men were compared with their brothers, the adjusted odds of overweight increased in an exponential way (linearly in logit) over the entire range of the birth weight scale. A within-family difference of 100 g in birth weight was associated with a within-family difference of 3.5% (99% confidence interval: 2.5-4.6) in the odds of overweight.

CONCLUSIONS

There is a positive within-family association between birth weight and the odds of overweight in young Norwegian men born at term.