Health-care costs of underweight, overweight and obesity: Australian population-based study.

Aim: Child health varies with body mass index (BMI), but it is unknown by what age or how much this attracts additional population health-care costs. We aimed to determine the (1) cross-sectional relationships between BMI and costs across the first decade of life and (2) in longitudinal analyses, whether costs increase with duration of underweight or obesity.

Participants: Baby (n = 4230) and Kindergarten (n = 4543) cohorts in the nationally representative Longitudinal Study of Australian Children.

Outcome: Medicare Benefits Scheme (including all general practitioner plus a large proportion of paediatrician visits) plus prescription medication costs to federal government from birth to sixth (Baby cohort) and fourth to tenth (Kindergarten cohort) birthdays.

Predictor: biennial BMI measurements over the same period.

Results: Among Australian children under 10 years of age, 5-6% were underweight, 11-18% overweight and 5-6% obese. Excess costs with low and high BMI became evident from age 4-5 years, with normal weight accruing the least, obesity the most, and underweight and overweight intermediate costs. Relative to overall between-child variation, these excess costs per child were very modest, with a maximum of $94 per year at age 4-5 years. Nonetheless, this projects to a substantial cost to government of approximately $13 million per annum for all Australian children aged less than 10 years.

Conclusions: Substantial excess population costs provide further economic justification for promoting healthy body weight. However, obese children's low individual excess health-care costs mean that effective treatments are likely to increase short-term costs to the public health purse during childhood.