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Strong evidence shows link between adiposity, some types of cancer

Evidential findings support the association between severe or morbid obesity and 11 types of cancer, mainly those of the digestive organs and hormone-related malignancies, according to an umbrella review of related literature published in British Medical Journal.

“Several meta-analyses support the link between obesity and cancer, but substantial heterogeneity exists between studies,” Maria Kyrgiou, PhD, MRCOG, from the department of surgery and cancer at Imperial College London and the West London Gynecological Cancer Center at Imperial Healthcare NHS Trust, and colleagues wrote. “The reported associations may be causal, but they may also be flawed, as inherent study biases such as residual confounding and selective reporting of positive results may exaggerate the effect of obesity on cancer.”

To determine the quality of evidence and the validity of previously reported associations between adiposity and risk of developing or dying from cancer, researchers performed a comprehensive evaluation of related meta-analyses and systematic reviews found on PubMed, Embase and Cochrane Database of Systematic Reviews.

They identified 204 meta-analyses from 49 publications that examined links between seven indices of adiposity — BMI, weight, weight gain, weight loss through bariatric surgery, hip circumference, waist circumference and waist-to-hip ratio — and developing or dying from 36 major types of cancers and their subtypes. Out of the 95 studies that included cohort studies and continuous obesity measures, 13% of reported associations for nine cancers were backed by strong evidence.

Kyrgiou and colleagues observed strong associations between increased BMI and higher risk for esophageal adenocarcinoma; colon and rectal cancer in men; biliary tract system and pancreatic cancer; endometrial cancer in premenopausal women; kidney cancer; and multiple myeloma. Weight gain was linked to higher risk for postmenopausal breast cancer in women who have never used hormone replacement therapy (HRT), and larger waist to hip circumference showed association with endometrial cancer. Researchers found that risk of postmenopausal breast cancer among women who never used HRT increased by 11% for every 5 kg gained in adulthood (RR = 1.11; 95% CI, 1.09-1.13) and the risk for endometrial cancer rose by 21% for each 0.1 increase in waist-to-hip ratio (RR = 1.21; 95% CI, 1.13-1.29). Among men, the risk for cancer for every 5 kg/m² increase in BMI ranged from 9% (RR = 1.09; 95% CI, 1.06-1.13) for rectal cancer to 56% (RR = 1.56; 95% CI, 1.34-1.81) for biliary tract system cancer. Weight gain was linked to risk for colorectal cancer, and high BMI was linked to risk for gallbladder, gastric cardia and ovarian cancers, and multiple myeloma mortality when researchers accounted for categorical measures of obesity.

“We found strong evidence to support the positive association between obesity and 11 of the 36 cancer sites and subtypes that we examined, predominantly comprising cancers of the digestive organs and hormone-related malignancies in women,” Kyrgiou and colleagues wrote. “To draw firmer conclusions we need better prospective studies and large consortiums with better assessment of the changing nature of body fatness and with comprehensive standardized reporting of analyses.” – by Savannah Demko

Disclosure: Kyrgiou reports no relevant financial disclosures.