Excess body fat, especially around the waistline, appears to be as important as body mass index (BMI) in increasing the risk for a range of cancers known to be associated with obesity, reveals a meta-analysis that underscores the importance of lifestyle on cancer risk.
An analysis of data on more than 43,000 individuals revealed that, while increases in BMI raised the risk of developing a group of 10 obesity-related cancers by 11%, similar increases in waist circumference and waist-to-hip ratio (WHR) raised the risk by 13% and 15%, respectively.
The research is published in the May 23 issue of the British Journal of Cancer.
"Our findings show that both BMI and where body fat is carried on the body can be good indicators of obesity-related cancer risk. Specifically, fat carried around the waist may be important for certain cancers but requires further investigation," commented lead researcher, Heinz Freisling, PhD, Section of Nutrition and Metabolism, International Agency for Research on Cancer, Lyon, France.
"To better reflect the underlying biology at play, we think it's important to study more than just BMI when looking at cancer risk. And our research adds further understanding to how people's body shape could increase their risk," he said in a statement.
Julie Sharp, head of health information at the charity Cancer Research UK, commented: "This study further highlights that, however you measure it, being overweight or obese can increase the risk of developing certain cancers, including breast and bowel."
"It's important that people are informed about ways to reduce their risk of cancer," she added.
Adiposity as Well as BMI
It is well known that high BMI is associated with many noncommunicable diseases, including cancer. However, it is less clear how well BMI captures the association between adiposity and cancer, with waist circumference and WHR believed to be better predictors of particular colon and postmenopausal breast cancers.
To more comprehensively examine the anthropometric determinants of obesity and their associations with cancer, the researchers conducted a meta-analysis of seven prospective studies in the Consortium on Health and Ageing: Network of Cohorts in Europe and the United States.
They collated harmonized individual-participant data from the studies and used multivariate Cox proportional hazards models separately for BMI, waist circumference, hip circumference, and WHR, with each obesity indicator analyzed as a continuous variable.
Data on 43,419 individuals from Denmark, Germany, Greece, the Netherlands, Northern Ireland, Norway, and Spain were included in the study. The mean age at study entry ranged from 54 to 67 years, and the prevalence of obesity ranged from 11% to 42%.
During a median follow-up of 12 years, there were 1656 cases of obesity-related cancer, which was defined as cancers of the postmenopausal female breast, colorectum, lower esophagus, gastric cardia, liver, gallbladder, pancreas, endometrium, ovary, and kidney.
Across all studies, BMI was associated with a significantly increased risk for obesity-related cancers, at a hazard ratio per 1–standard deviation (SD) increment of 1.11. Similar associations were seen for waist circumference and WHR, at respective hazard ratios of 1.13 and 1.15.
While hip circumference was positively associated with an overall increased risk for obesity-related cancers, at a hazard ratio per 1-SD increment of 1.09, it did not reach statistical significance.
There was also a clear dose–response relationship between all adiposity measures, aside from WHR, and obesity-related cancers.
All four obesity measures were associated with a significantly increased risk for colorectal cancer, at hazard ratios per 1-SD increment of 1.16 for BMI, 1.21 for waist circumference, 1.15 for hip circumference, and 1.20 for WHR.
For postmenopausal breast cancer, there was a significant positive association with BMI after adjustment for hip and waist circumference, at a hazard ratio per 1-SD increment of 1.15.
When the researchers further stratified the participants by hormone therapy use, they found that never-users had a significantly increased risk for postmenopausal breast cancer compared with ever-users of approximately 20% for each obesity measure.
"General adiposity as measured by BMI and body fat distribution as measured by WC [waist circumference], HC [hip circumference], or WHR show comparable positive associations with obesity-related cancers combined, with CRC [colorectal cancer], and with postmenopausal breast cancer," the team concludes.
While noting that the effect modification by hormone therapy on the risk for postmenopausal breast cancer "needs further investigation," they add: "Overall, our results underscore the importance of avoiding excess body fatness for cancer prevention irrespective of age and gender."