body mass index and Cancer

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High Body Mass Index Increases Risk of Developing Cancer CME/CE

News Author: Roxanne Nelson

CME Author: Hien T. Nghiem, MD

Disclosures

Release Date: November 19, 2007; Valid for credit through November 19, 2008 Credits Available

Physicians - maximum of 0.25 AMA PRA Category 1 Credit(s)™ for physicians;

Family Physicians - up to 0.25 AAFP Prescribed credit(s) for physicians;

Nurses - 0.25 nursing contact hours (None of these credits is in the area of pharmacology)

November 19, 2007— An increasing body mass index (BMI) is associated with a significant increase in the risk for certain types of cancer, report researchers conducting the Million Women Study, a cohort study of women in the United Kingdom. Among postmenopausal women residing in the United Kingdom, 5% of all cancers are associated with excess body weight, according to a study published in the November 7 Online First issue of the BMJ. This is particularly true for endometrial cancer and adenocarcinoma of the esophagus, as approximately half of all cases within this population are attributed to being overweight or obese.

In an accompanying editorial, Eugenia E. Calle, PhD, from the American Cancer Society in Atlanta, Georgia, notes that there is already substantial observational evidence suggesting that increasing adiposity, both overall and central, is associated with an increasing risk for a number of cancers.

"The strongest empirical support for mechanisms to link obesity and cancer risk involves the metabolic and endocrine effects of obesity, and the alterations they induce in the production of peptide and steroid hormones," Dr. Calle writes. "The worldwide obesity epidemic shows no signs of abating, so insight into the mechanisms by which obesity contributes to the formation and progression of tumours is urgently needed, as are new approaches to intervene in this process."

Gillian Reeves, PhD, a statistical epidemiologist at the Cancer Epidemiology Unit, University of Oxford in the United Kingdom, and colleagues, evaluated the relationship between BMI and cancer in 1.2 million British women between the ages of 50 and 64 years, who participated in the Million Women Study. The researchers note that according to national statistics, currently 23% of all women in the United Kingdom are obese and 34% are overweight.

For their study, Dr. Reeves and her team assessed the relative risks (RRs) for incidence and mortality for all cancers, and for 17 specific types of cancer, according to BMI. The data were then adjusted for numerous confounders including age, geographic region, socioeconomic status, age at first birth, parity, smoking status, alcohol intake, physical activity, years since menopause, and use of hormone replacement therapy.

The follow-up period for cancer incidence averaged 5.4 years, during which time 45,037 incident cancers occurred. Average follow-up time for cancer-related mortality was 7.0 years, and 17,203 cancer-related deaths occurred during this time.

The researchers observed that women with a higher BMI tended to come from a lower socioeconomic class; had more children vs those with a lower BMI; and were also less likely to smoke, drink, and use hormone replacement therapy. But after adjusting the data for confounders, they found that increasing BMI was associated with an increased incidence of endometrial cancer, adenocarcinoma of the esophagus, kidney cancer, leukemia, multiple myeloma, pancreatic cancer, non-Hodgkin's lymphoma, ovarian cancer, and breast cancer in postmenopausal women and colorectal cancer in premenopausal women.

They note that there were also substantial differences in cancer risk based on menopausal status. For endometrial cancer, both premenopausal and postmenopausal women had a significantly increased risk with increasing BMI, but the risk was far greater for the latter. Positive trends in risk with BMI were seen in premenopausal women for colorectal cancer and malignant melanoma, and although an increased BMI was associated with a lower risk for breast cancer in premenopausal women, it raised the risk in postmenopausal women.

The results of their analysis also showed a significant inverse association between BMI and squamous cell carcinoma of the esophagus and lung cancer. In general, the relationship between BMI and cancer-related mortality was similar to that for incidence.

"Overall, these findings imply that 6000 new cancers annually in postmenopausal women in the UK are due to being overweight or obese, of which 4800 are due to obesity," the study authors conclude.

The Million Women Study is supported by Cancer Research United Kingdom, the UK Medical Research Council, and the UK National Health Service Breast Screening Programme. The study authors have disclosed no relevant financial relationships.

Dr. Calle has disclosed no relevant financial relationships.

BMJ. Published online November 7, 2007.

Clinical Context

Obesity is known to be an important cause of type 2 diabetes mellitus, hypertension, and dyslipidemia. In addition, the adverse metabolic effects of excess body fat accelerate the development of atheroma and increase the risk for coronary heart disease, stroke, and early death. Currently, there is substantial evidence that supports the link between increasing adiposity and a higher risk for many cancers. These cancers include adenocarcinoma of the esophagus, endometrial cancer, kidney cancer, and postmenopausal breast cancer.

The aim of this study was to examine the relationship between BMI and cancer incidence and mortality.

Study Highlights

In this prospective cohort study, 1.2 million women aged 50 to 64 years from the United Kingdom were recruited into the Million Women Study between 1996 and 2001.

On average, they were followed up for 5.4 years for cancer incidence and 7.0 years for cancer mortality.

Women with a BMI of 25 to 29.9 kg/m2 were defined as overweight, and women with a BMI of 30 kg/m2 or more were obese, in accordance with the World Health Organization.

The main outcome measures included RRs for incidence and mortality for all cancers and for 17 specific types of cancer according to BMI.

Data were adjusted for several confounders including age, geographic region, socioeconomic status, age at first birth, parity, smoking status, alcohol intake, physical activity, years since menopause, and use of hormone replacement therapy.

Results revealed that 45,037 incident cancers and 17,203 deaths from cancer occurred in the follow-up period.

Increasing BMI was associated with an increased incidence of endometrial cancer (trend in RR per 10 units, 2.89; 95% confidence interval [CI], 2.62 - 3.18), adenocarcinoma of the esophagus (RR, 2.38; 95% CI, 1.59 - 3.56), kidney cancer (RR, 1.53; 95% CI, 1.27 - 1.84), leukemia (RR, 1.50; 95% CI, 1.23 - 1.83), multiple myeloma (RR, 1.31; 95% CI, 1.04 - 1.65), pancreatic cancer (RR, 1.24; 95% CI, 1.03 - 1.48), non-Hodgkin's lymphoma (RR, 1.17; 95% CI, 1.03 - 1.34), ovarian cancer (RR, 1.14; 95% CI, 1.03 - 1.27), all cancers combined (RR, 1.12; 95% CI, 1.09 - 1.14), breast cancer in postmenopausal women (RR, 1.40; 95% CI, 1.31 - 1.49), and colorectal cancer in premenopausal women (RR, 1.61; 95% CI, 1.05 - 2.48).

In general, the relationship between BMI and mortality was similar to that for incidence.

For colorectal cancer, malignant melanoma, and breast and endometrial cancers, the effect of BMI on risk differed significantly according to menopausal status.

The estimated proportion of all cancers attributable to being overweight or obese among postmenopausal women was 5%.

For endometrial cancer and adenocarcinoma of the esophagus, approximately half of cases (51% and 48%, respectively) were attributable to being overweight or obese.

Pearls for Practice

There is evidence to support that obesity is linked to adenocarcinoma of the esophagus, endometrial cancer, kidney cancer, and postmenopausal breast cancer.

Among postmenopausal women in this study, 5% of all cancers are attributable to women being overweight or obese. Increasing BMI is associated with a significant increase in the risk for cancer for 10 of 17 specific types examined.