Background

Obesity is increasingly recognized as a preventable cause of cancer. We assessed the association between adolescent body-mass index (BMI) and cancer incidence and mortality in midlife.

Methods

BMI was measured from 1967 through 2010 in 2,294,139 adolescents (16-19 year; 59.5% men) and classified according to the US-Center for Disease Control percentiles. Data of these adolescents was linked to the Israeli National Cancer Registry of the Israeli Ministry of health. Primary outcome was incident cancer through 12/31/2012. Secondary outcome was all-cause mortality through 12/31/2017 among patients with cancer. Cox models were applied.

Results

During 29,542,735 and 18,044,863 person-years of follow-up, there were 26,353 and 29,488 incident cases of cancer among men and women, respectively, with 8,351 and 5,218 deaths among men and women who developed cancer, respectively. There was a graded increase in cancer incidence across BMI percentiles. The adjusted hazard ratio (HR) was 1.26 (1.18-1.35) among obese men (reference, 5th-49th BMI percentile). Among women, obesity was inversely associated with incident cervix and breast cancer, but conferred higher mortality risk. There was an adjusted HR of 1.27 (1.13-1.44) among obese women (excluding breast and cervix cancer). Overweight was associated with increased cancer risk after 10 years in both sexes. The association between obesity and cancer incidence was accentuated in the recent vs. early period of the study. The projected population attributable risk of high BMI (≥85th percentile) were 5.1% (4.2%-6.1%) and 5.7% (4.2%-7.3%), for men and women, respectively.

Conclusions

The stronger association between adolescent BMI and cancer measured in recent years, along with the rising prevalence of adolescent obesity suggest increasing future burden of obesity-related cancers.