Cancer incidence is rising among adults aged 20 to 49 in England, and established lifestyle risks do not fully explain the pattern. Researchers analyzed national cancer-registration data from 2001 to 2019 alongside health-survey data on smoking, alcohol, diet, body mass index and physical activity.
Eleven cancers linked to behavioral risk factors increased among younger adults. Colorectal and ovarian cancers rose in younger people without the same increase among adults aged 50 and older. Incidence also increased faster among younger women for endometrial, kidney, pancreatic, multiple myeloma and thyroid cancers. Among men, multiple myeloma was the only cancer in the analysis rising significantly faster in the younger group.
Excess body weight was the only major risk factor that consistently increased over the period and was associated with the largest number of cancer types examined. In 2019, researchers estimated that excess weight accounted for between 5% of ovarian cancer cases and 37% of endometrial cancer cases.
The other established risks did not move in a direction that could readily account for the broader increase. Smoking, alcohol use, physical inactivity and dietary indicators were generally stable or declining among younger adults. Average daily red-meat consumption fell from 38 grams to 17 grams among younger men and from 22 grams to 10 grams among younger women between 2008 and 2018.
The analysis linked smoking with liver, colorectal, oral, pancreatic, kidney and ovarian cancers; alcohol with liver, colorectal, oral and breast cancers; physical inactivity with colorectal, breast and endometrial cancers; and dietary factors with colorectal cancer. Even where those factors remained important contributors to overall cancer burden, their population trends generally did not match the rise in early-onset disease.
The researchers said possible explanations include age-specific exposures, differing susceptibility and changes in diagnosis or screening. They also pointed to emerging possibilities such as altered gut microbiome populations and exposures during childhood or before birth. These possibilities remain unproven, and the observational analysis cannot establish that any particular factor caused the cancer increases.
The study was limited by gaps in long-term national data for some risk factors, its focus on England rather than the whole United Kingdom and an assumed 10-year delay between exposure and cancer development. It also found that several younger-adult cancer rates had stabilized or declined in recent years, while the absolute number of cases remained much higher among older adults.
A separate UK research effort is now recruiting up to 250,000 participants for a long-term study of early-onset bowel cancer. Participants will provide information on diet, lifestyle, environment and health, with smaller groups contributing detailed food records, blood samples and stool samples. The goal is to compare these exposures with later health outcomes as researchers investigate why bowel cancer is increasing in younger adults.