People who are obese have a greater risk of developing and dying from several types of cancer including cancers of the breast, ovary, kidney, pancreas, colon, rectum and bone marrow, a research review from Imperial College London confirms.
Excess weight is thought to influence the odds of developing and dying from a wide variety of tumors. The new study found “strong evidence” supporting this connection for just 11 cancers.
For the current study, researchers analyzed results from 204 previously published studies exploring the connection between obesity, weight gain, waist circumference and 36 different cancers.
Researchers looked in particular for evidence that the previous results might have exaggerated the link between obesity and cancer or found a connection that was too small to rule out the possibility that it was due to chance.
They found the strongest links were between obesity and cancers of the digestive organs and for hormone-related tumors in women.
When researchers looked at what’s known as body mass index (BMI), a ratio of weight to height, they found increases in BMI tied to a higher risk of developing cancers in the esophagus, bone marrow, biliary tract system, pancreas and kidney. Upticks in BMI were also linked to greater odds of colon and rectal cancers in men as well as endometrial cancer in younger women.
A BMI between 18.5 and 24.9 is considered a healthy weight, while 25 to 29.9 is overweight, 30 or above is obese and 40 or higher is what's known as morbidly obese. (Determine your BMI.)
The increased risk of cancer for every 5-unit gain in BMI ranged from 9 percent for rectal cancer among men to 56 percent for tumors in the biliary tract system.
Women, weight gain, waist size and cancer risk
For women, weight gain and extra belly fat, a measurement known as waist-to-hip circumference ratio, were also associated with an increased risk of certain cancers.
After menopause, women’s risk of breast cancer increased by 11 percent for every 5 kilograms (11 pounds) of weight they gained during adulthood. This was in women who didn’t take hormones to ease menopause symptoms, a treatment that is independently linked to an increased risk of breast cancer.
As women added more fat around the midsection, every 0.1 unit increase in waist-to-hip ratio was associated with a 21 percent jump in the odds of endometrial cancer.
Researchers found strong evidence linking weight gain to colorectal cancer. They also found a strong connection between BMI increases and getting cancers of the gallbladder, stomach and ovaries, as well as dying from bone marrow tumors.
Avoiding adult weight gain important for cancer prevention
One limitation: the review looked at observational studies. It did not assess randomized controlled trials designed to prove that obesity directly causes cancer.
More research is needed that assesses changes in body fat over time to better understand how obesity directly influences the risk of getting cancer or dying from the disease.
Even so, the take-home message is that avoiding weight gain through adult years is important. If you are overweight focus first on not gaining any more weight. Losing excess weight can lower cancer risk.
Source: The BMJ, online February 28, 2017.
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