Being overweight or obese has long been linked to cancer, but new research suggests that when weight is gained during adulthood may significantly influence that risk. A large Swedish study now indicates that the timing and pace of weight gain, as well as sex, play important roles in how body fat relates to different cancers.
Researchers analyzed health and weight data from just over 630,000 people in Sweden who had multiple body weight measurements recorded between the ages of 17 and 60. They then tracked cancer diagnoses over time and compared them with individual weight trajectories. The findings, presented at the European Congress on Obesity and currently available as a preprint, have not yet undergone peer review.
How the study tracked weight and cancer
The team reconstructed each participant’s weight trajectory across adulthood rather than focusing on a single point in time. Using repeated measurements, they estimated how quickly people gained weight at different ages and how early in adulthood they developed obesity. These profiles were then linked to data from the national cancer registry.
Unlike many earlier studies that examined weight only during midlife, this approach allowed the researchers to distinguish between initial adult weight and subsequent weight changes. They argue that this life-course perspective reveals patterns that are overlooked when weight is assessed only once. It also helps clarify which stages of adulthood may be particularly sensitive for cancer risk.
Weight gain timing and cancer patterns
Rapid weight gain at almost any point during adulthood was associated with an increased risk of several cancers. In men, the strongest associations were observed for liver cancer and esophageal adenocarcinoma, particularly when weight gain occurred before age 45. In women, weight gain after age 30 was most strongly associated with an increased risk of endometrial cancer.
For both sexes, faster weight gain was linked to elevated risks of renal cell carcinoma and pituitary tumors. These associations suggest that metabolic changes and hormonal disruptions related to increasing body fat may affect multiple organs. The researchers note that these patterns persisted after accounting for baseline weight in early adulthood.
Early obesity and adolescent weight
The study also found that the earlier a person developed obesity during adulthood, the higher their overall cancer risk tended to be. Individuals who became obese at a younger age were exposed to excess body fat for a longer period, which may amplify harmful effects such as chronic inflammation and insulin resistance.
For some cancers, including pancreatic cancer, the strongest association was with body weight at age 17 rather than later weight changes. This suggests that weight during late adolescence may influence long-term cancer susceptibility, possibly through early metabolic or hormonal programming that persists into adulthood.
Different risks for men and women
The findings highlight notable differences between men and women in how weight gain over time relates to specific cancers. In men, earlier weight gain appeared particularly important, with stronger associations observed for esophageal and liver cancers before midlife. Conditions such as fatty liver disease and gastroesophageal reflux may mediate some of these relationships.
For women, weight gain during their 30s and 40s was more strongly associated with endometrial and potentially other hormone-sensitive cancers. The authors suggest this may reflect interactions between increasing fat mass and changing sex hormone levels during middle age, including the menopausal transition.
Limits, context and public health impact
Because the study is observational, it cannot prove that weight gain directly causes the increased cancer risks identified. The data did not include detailed information on diet, physical activity, smoking, or alcohol consumption, all of which can influence both body weight and cancer risk. These unmeasured factors may partially explain some of the observed associations.
Even so, the results are broadly consistent with previous research linking obesity to at least 13 types of cancer. A related analysis by the same research group has also shown that earlier obesity is associated with higher overall mortality, reinforcing concerns about the long-term health consequences of weight gain during young adulthood.
The authors argue that cancer prevention strategies should not only focus on reducing obesity overall but should also consider the timing of weight gain. They suggest that maintaining a healthy weight from adolescence through early and middle adulthood could provide substantial health benefits. Targeted interventions tailored by age and sex may help curb rising cancer rates in countries where obesity is becoming increasingly common.
Experts who were not involved in the study note that its large sample size and detailed weight histories add important nuance to the evidence base. However, they emphasize the need for peer review and further studies in other populations. Future research could explore how specific lifestyle changes at different ages might mitigate cancer risks associated with earlier weight gain.
Despite the remaining uncertainties, the emerging message is that weight management is a lifelong concern rather than an issue confined to midlife. Minimizing rapid weight gain, particularly during early adulthood, could be a critical component of broader efforts to reduce the global burden of cancer.