# Association of childhood-to-adulthood body size change with cancer risk: UK Biobank prospective cohort

## TL;DR

This study shows that becoming overweight or obese in adulthood increases cancer risk, regardless of childhood body size.

## Contribution

The study provides new evidence on how adult BMI, rather than childhood size, primarily drives cancer risk.

## Key findings

- Overweight or obesity in adulthood significantly increases the risk of obesity-related cancers.
- Childhood body size had little impact on cancer risk compared to adult BMI.
- Higher childhood body size was linked to lower postmenopausal breast cancer risk.

## Abstract

While excess weight in adulthood and childhood has been associated with increased cancer risk, the link between body size change from childhood to adulthood and cancer risk requires further investigation. We aimed to examine the associations of childhood-to-adulthood body size change with the risk of obesity-related cancers.

We used data from the UK Biobank, a prospective population-based cohort study. The main exposure was childhood-to-adulthood body size change, constructed from self-reported body size at age 10 (categories: thinner, average, and plumper than average) and measured body mass index (BMI) at recruitment (normal weight, overweight, and obesity). Primary outcome was obesity-related cancer (13 different cancer types).

Among 448,936 participants (mean [SD] age, 56.2 [8.1] years; 240,023 were female [53.5%]) and during a median follow-up of 11.7 years (interquartile range [10.9–12.4]), 21,289 incident obesity-related cancer cases were recorded. Most participants were either overweight (42.6%) or had obesity (24.4%) at recruitment, while only a minority (16.0%) reported to have been plumper than average at age 10. Having a larger body size in childhood was strongly associated with having overweight or obesity in adulthood. Compared to participants with average childhood and normal adulthood body size, participants with overweight or obesity in adulthood had a significantly increased risk of obesity-related cancers, regardless of the childhood body size (adjusted hazard ratios ranged from 1.15 [95% CI, 1.06–1.24] to 1.61 [95% CI, 1.50–1.73]). The strength of the association was mostly determined by adulthood BMI, and similar patterns were observed for colorectal, endometrial, kidney, pancreatic, and esophageal cancer. However, a larger body size in childhood was associated with a lower risk of postmenopausal breast cancer (adjusted hazard ratio, 0.86 [95% CI, 0.79–0.93]).

While larger body size in childhood predisposes individuals to overweight and obesity in adulthood, maintaining a healthy weight in adulthood may help mitigate the risk of obesity-related cancers. Our findings highlight the importance of preventing and reducing overweight and obesity in adulthood for primary cancer prevention.

The online version contains supplementary material available at 10.1186/s12916-025-04052-8.