OBJECTIVE: To test the hypothesis that obesity is associated with impaired 
cognitive outcomes in the pre-school years.
METHODS: Associations were examined between weight status at age 3-5 years and 
cognitive performance at age 5 years. Cognitive outcome measures were tests of 
pattern construction (visuospatial skills), naming vocabulary (expressive 
language skills), and picture similarity (reasoning skills). The sample was the 
UK Millennium Cohort Study (n = 12,349 participants).
RESULTS: Boys with obesity at 3 years had significantly lower performance in 
pattern construction at age 5 years compared to those of a healthy weight, even 
after controlling for confounders (β = -0.029, P = 0.03). Controlling for 
confounders, boys who developed obesity between the ages of 3 and 5 years had 
lower scores in pattern construction (β = -0.03, P = 0.03). "Growing out" of 
obesity had a positive association with picture similarity performance in girls 
(β = 0.03, P = 0.04).
CONCLUSIONS: Obesity in the pre-school years was associated with poorer outcomes 
for some cognitive measures in this study. Stronger relationships between 
obesity and cognition or educational attainment may emerge later in childhood.