BACKGROUND: Overweight and obesity are risk factors for cardiovascular disease. 
There is also an association between body mass index (BMI) and cognitive 
ability. Since low birth weight is associated with adult metabolic disease, 
particularly in obese subjects, the question emerges whether obesity has an 
additional negative effect on cognitive function in subjects with low birth 
weight.
OBJECTIVES: The aim was to analyse whether overweight or obesity influence 
intellectual performance in young adults with particular focus on those with a 
low birth weight.
METHODS: Data were collected from the Swedish Medical Birth Register on 620,834 
males born between 1973 and 1988 and matched to results on intellectual 
performance and BMI at conscription.
RESULTS: The risk for low intellectual performance was higher for those with 
high BMI compared to those with normal. The highest risk was found among 
subjects with low birth weight and overweight or obesity in young adulthood 
(odds ratios, 1.98 [1.73-2.22] and 2.59 [2.00-3.34], respectively). However, 
subjects with further high birth weight and a high BMI at conscription had no 
further increased risk.
CONCLUSIONS: Overweight and obesity are associated with an increased risk of 
subnormal intellectual performance in young adult males. Subjects with low birth 
weight and adolescent overweight/obesity are at particular risk of subnormal 
performance. A high birth weight increases the risk for obesity, but a high 
adult BMI does not further increase the risk for subnormal performance.