People who become overweight at younger adult ages have significantly greater cancer risk than their slimmer peers. Visceral fat tissue is very active, producing chronic inflammation through a range of mechanisms including the production of greater numbers of lingering senescent cells. This sort of tissue environment is more hospitable to the development of cancer. Cancer risk is far from the only downside of carrying excess visceral fat tissue, of course: one can expect a shorter, less healthy life on all fronts, accompanied with a raised lifetime medical cost.

Obesity is an established risk factor for several cancers. Adult weight gain has been associated with increased cancer risk, but studies on timing and duration of adult weight gain are relatively scarce. We examined the impact of body mass index (BMI) and weight changes over time, as well as the timing and duration of excess weight, on obesity- and non-obesity-related cancers. We pooled health data from six European cohorts and included 221,274 individuals with two or more height and weight measurements during 1972-2014. Several BMI and weight measures were constructed. Cancer cases were identified through linkage with national cancer registries. Hazard ratios (HRs) of cancer were derived from time-dependent Cox-regression models.

During follow-up, 27,881 cancer cases were diagnosed; 9,761 were obesity-related. The HR of all obesity-related cancers increased with increasing BMI at first and last measurement, maximum BMI and longer duration of overweight (men only) and obesity. Participants who were overweight before age 40 years had an HR of obesity-related cancers of 1.16 and 1.15 in men and women, respectively, compared with those who were not overweight. The risk increase was particularly high for endometrial cancer (70%), male renal-cell cancer (58%) and male colon cancer (29%). No positive associations were seen for cancers not regarded as obesity-related. In conclusion, adult weight gain was associated with increased risk of several major cancers. The degree, timing, and duration of overweight and obesity also seemed to be important. Preventing weight gain may reduce the cancer risk.