Background: Obesity is known to track from early life into adult life.
Objective: To examine the relation of obesity in adult life to growth and living conditions during childhood.
Design: Birth cohort study.
Participants: A total of 4515 people (2135 men and 2380 women) who were born at Helsinki University Central Hospital between 1934 and 1944, who attended child welfare clinics and were still resident in Finland in the year 2000.
Measurements: Incidence of obesity based upon lifetime maximum body mass index (BMI) ascertained from a postal questionnaire and defined as a BMI>or=30 kg/m(2). The main explanatory measurements were size at birth, childhood growth, and socioeconomic status in childhood and in adult life.
Results: The cumulative incidence of obesity was 33.8% in men and 32.4% in women. The incidence rose with increasing body size at birth. From birth the mean weight and BMI of people who later became obese exceeded the average and remained above average at a statistically significant level at all ages from 6 months to 12 y. Childhood BMI was a stronger predictor of adult obesity than body size at birth. A higher maternal BMI in pregnancy was associated with a more rapid childhood growth and an increased risk of becoming obese in adult life. Higher socioeconomic status and better educational attainment were associated with a lower prevalence of obesity. There was no association between the duration of breastfeeding and later obesity.
Conclusions: These results emphasize the importance of early life factors in the pathogenesis of adult obesity.