In a recent study published in The Lancet Regional Health - Europe, researchers evaluated the associations between body mass index (BMI) and the risk of obesity-related cancers.
Study: Body mass index and risk of over 100 cancer forms and subtypes in 4.1 million individuals in Sweden: the Obesity and Disease Development Sweden (ODDS) pooled cohort study. Image Credit: myboys.me/Shutterstock.com
Introduction
The high prevalence of obesity and overweight emphasizes the need to elucidate their effects on morbidity. Increasing evidence suggests obesity to be a preventable cause of some cancers.
A 2016 International Agency for Research on Cancer (IARC) report established associations between BMI and 13 cancers.
A later umbrella review confirmed a majority of these cancers to be obesity-related. While observational studies have assessed associations between BMI and the risk of cancer, they have rarely focused on morphological cancer subtypes.
About the study
In the present study, researchers explored potential obesity-related cancers and subtypes and quantified associations between BMI and obesity-related cancers. Data were used from the Obesity and Disease Development Sweden study.
The Swedish Cancer Register identified cancer diagnoses between 1963 and 2019 and classified cancers using codes.
The 13 cancers reported by IARC to be obesity-related were established obesity-related cancers. In addition, potential obesity-related cancers were identified using an explorative decision algorithm and defined as those positively associated with increased risk of obesity relative to normal weight or per 5 kg/m2 increased BMI.
BMI was assessed in relation to cancer risk in categories (underweight, overweight, etc.) or per 5 kg/m2 if the number of cases was at least 250 or 100, respectively.
Cox regression models estimated hazard ratios (HRs) and 95% confidence intervals. Models were stratified by birth year and sex and adjusted for baseline age, mode of height and weight assessment, education, birth country, and marital status.
Cox models were repeated for smoking-related cancers in people with available smoking information. The Wald test was used to assess potential sex interactions.
Findings
Overall, 4.14 million individuals were included; 2.01 million were females, and 2.12 million were males, with an average baseline age of 31.3 and 23.1, respectively. The average BMI was 22.5 kg/m2 for males and 24 kg/m2 for females.
The prevalence of obesity was 9% in females and 3% in males. After 24.2 years of (median) follow-up, 332,501 cancer cases were recorded: 139,685 in females and 192,816 in males.
The median age of females and males at cancer diagnosis was 55.7 and 63.1, respectively. Obesity was associated with a higher risk of 18 cancers (16 cancers in females and 15 in males) relative to normal weight or per 5 kg/m2 higher BMI.
These were potential obesity-related cancers previously not established as obesity-related and accounted for 15% of all cases. In females, these were cancers of the cervix, head and neck (squamous cell carcinoma), vulva, and nodular melanoma.
In males, these were cancers of the penis, head and neck (adenocarcinoma) and malignant melanoma.
In both sexes, these included cancers of the small intestine, gastric, oral cavity, paranasal and nasal sinuses, biliary tract, adrenal glands, pituitary gland, pancreatic islets, connective tissue, parathyroid gland, myeloid neoplasms, and lymphoid neoplasms.
There were sex interactions for malignant melanoma, lymphoid neoplasms, and lip, head and neck, tongue, and connective tissue cancers.
Further, specific subtypes of some potential obesity-related cancers were more strongly associated with BMI than other subtypes. For smoking-related cancers, the association with BMI was sustained for some cancers but diminished for others when adjusted for smoking status.
Besides, obesity was associated with a higher risk of all established obesity-related cancers, which accounted for a quarter of all cases.
The HRs for potential and established obesity-related cancers were 1.17 and 1.24 in males and 1.13 and 1.12 in females, respectively. In males, the absolute risk of a potential obesity-related cancer by age 80 was 5.7 for obesity and 5.5% for normal weight.
In females, these estimates were 4.2% for obesity and 3.5% for normal weight. Further, the combined risk of established and potential obesity-related cancers by age 80 was 14.2% for obesity and 12% for normal weight in males. The corresponding estimates in females were 18.7% and 16.3%, respectively.
Conclusions
In sum, the study identified 18 potential obesity-related cancers previously not established as obesity-related. These included cancers of the gastrointestinal tract, endocrine organs, head and neck, genitals, hematological malignancies, and malignant melanoma.
The association of BMI with these cancers was slightly weaker than with established obesity-related cancers in males but was comparable in females. Further studies accounting for cancer-specific confounders are warranted to corroborate these findings.
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