Obesity and sedentary lifestyle is the second leading cause of preventable illness and premature death in the United States; it’s second only to tobacco use. We have also known for some time that excess weight is associated with an increased risk of developing some cancers.
Two recently published large studies expand our knowledge by better defining the extent of these associations. The two studies do not exactly agree on which cancers are strongly associated with obesity since the studies utilized different evaluation strategies of the data. Thus, the studies did differ somewhat in the strength of the associations and conclusions regarding causality.
One of the studies published by the British Medical Journal is a massive examination of the associations between obesity and the risk of cancer.
Called an “umbrella review” it combines the results of other large collections of studies called “meta-analyses.” In total, the authors examine 204 meta-analyses involving 507 unique studies and the associations with obesity to 36 primary cancers. Strong evidence links obesity with increased risk for nine cancers including cancers of the esophagus (adenocarcinoma), colon and rectum in men, biliary tract, pancreas, kidney, endometrium (uterus) and breast in postmenopausal women, and multiple myeloma.
Additionally, highly suggestive but not conclusive evidence was found for liver, stomach, ovarian and thyroid cancers.
In this British Medical Journal study, the heart of the analysis was 95 meta-analyses that used a continuous scale of excess body fat and demonstrated a general trend of progressively higher risk with increasing body fat, commonly referred to as BMI. Other measures of excess fat included waist and hip circumference, weight, waist-to-hip ratio, and weight gain.
The other study was conducted by the International Agency for Research on Cancer. It also concludes, from reviewing an assortment of different types of studies, that excess body fat causes an increased risk for the nine cancers listed in the British Medical Journal study, but also adds obesity as causative in liver, gallbladder, thyroid, ovary and stomach cancers. As one can observe, the list of cancers and strength of evidence differs slightly in the two studies, but the concordance of the conclusions, mostly regarding digestive-organ cancers and female hormone-related malignancies, is striking and compelling.
These results are also largely consistent with a previous report issued by the World Cancer Research Fund that concluded that there is convincing evidence indicating a causal relationship between obesity with seven cancers including the esophagus, pancreas, rectum and colon, kidney, liver, and breast and uterus (postmenopausal). The two newer analyses extend our knowledge regarding additional cancers.
Cancer is the leading cause of death worldwide and the association between excess body fat and the risk of cancer is undeniable. It’s obvious that preventing obesity can reduce the rates of many cancers as well as other chronic conditions including heart disease, stroke, hypertension and diabetes. One-third of children and adolescents ages 6 to 19 are overweight and more than 1 in 6 of them are obese. Two- thirds of adults are overweight and one-third is obese.
Obesity too often begins in childhood, and once established, it’s commonly lifelong and then perpetuated from generation to generation. The human and financial costs of obesity to our economy and health-care system are staggering. Yet, our society is more than willing to pay for treating the consequences of obesity but not to pay for the public health programs and initiatives to prevent it. And Indiana is among the worst states in both obesity rates and public health funding.
Richard Feldman, M.D., is an Indianapolis family physician and the former Indiana State Health commissioner. Send comments to [email protected].