Wednesday, September 7, 2011

Obesity increases risk of multiple myeloma – overwhelming evidence.

In our Prevention Snapshot we refer to data from a thorough analysis reported by Renehan who combined prospective cohort data separately for men (7 studies) and women (6 studies) and observed a significant increase in relative risk of 1.11 for a 5 unit increase in BMI for men 1. This meta-analysis also reported no meaningful variation in the results among the studies evaluating BMI and multiple myeloma. 

A subsequent updated analysis reported in full this summer by Wallin and Larsson 2 also summarize the prospective studies evaluating the association of body mass index and the risk of being diagnosed with multiple myeloma. For this study the authors searched for and identified published studies through January 26, 2011. A total of 20 studies (15 on incidence of multiple myeloma and 5 on risk of mortality) were included. Compared to individuals in the normal weight category, the risk of multiple myeloma was statistically significant for the overweight (RR, 1.12; CI, 1.07-1.18) giving a 12 percent increase, and for obese men and women (RR, 1.21; CI, 1.08-1.35), a 21 percent increase in risk compared to average weight adults. The risk estimates for mortality from myeloma were somewhat higher.


Why does this matter?
As I recently noted, 30 years ago when Doll and Peto reviewed the evidence on causes of cancer 3, and considered overweight under the category of nutrition (over-nutrition), they did not separate out any clear link to specific cancers or a percentage of all cancers that could be avoided through healthy weight maintenance. In the past 30 years the study of weight, weight gain, overweight obesity and cancer has refined our understanding of how much cancer is caused by excess gain in weight over adult years.

The association between cancer and obesity is now well established in the literature. The 2002 IARC report on Prevention Report on Weight Control and Physical Activity listed obesity and lack of physical activity as causes of cancer incidence and mortality 4. Specifically, obesity was described as a cause of esophageal, colon, uterine, kidney and post-menopausal breast cancer. Data from the ACS Cancer Prevention Study II, which followed more than 1 million men and women for an average of 16 years, showed an additional link to cancers of the prostate and pancreas, as well as to non-Hodgkin lymphoma and myeloma 5. That study concluded that 16–20% of cancer deaths among women and 14% of cancer deaths among men were attributable to obesity. Furthermore, the IARC monograph also reported that there was sufficient evidence to conclude that lack of physical activity increased the risk of breast and colon cancer — two of the most cancers in the US.

Since that report, numerous additional studies have been published and the synthesis by Wallin brings the data into sharp focus for myeloma.

We can now be confident in understanding that obesity causes many cancers (see our report on obesity and cancer. We note that the evidence is consistent across many studies, conducted in the US, Europe, Australia, and Asia. As we note in our Knol on Obesity, many chronic conditions are caused by excess weight and the burden to society is substantial. Myeloma is now yet another malignancy that is caused by excess weight. Our quick tips for keeping weight in check can help us all moving forward.


Related CNiC Posts

Obesity, Diabetes, and Cancer

Obesity: Disturbing Rates Even if Trends Show a Glimmer of Hope

Obesity Causes Lymphoma and Myeloma


Literature Cited

1. Renehan AG, Tyson M, Egger M, Heller RF, Zwahlen M. Body-mass index and incidence of cancer: a systematic review and meta-analysis of prospective observational studies. Lancet. Feb 16 2008;371:569-578.

2. Wallin A, Larsson SC. Body mass index and risk of multiple myeloma: A meta-analysis of prospective studies. Eur J Cancer. 2011;47:1606-15.

3. Doll R, Peto R. The Causes of Cancer: Quantitative Estimates of Avoidable Risks of Cancer in the United States Today. New York: Oxford University Press; 1981.

4. International Agency for Research on Cancer. Weight Control and Physical Activity. Vol 6. Lyon: International Agency for Research on Cancer; 2002.

5. Calle EE, Rodriguez C, Walker-Thurmond K, Thun MJ. Overweight, obesity, and mortality from cancer in a prospectively studied cohort of U.S. adults. N Engl J Med. Apr 24 2003;348(17):1625-1638.

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