Obesity and Cancer, Part 3

by National Cancer Institute

(Page 3 of 4)

10. Does obesity increase the risk of cancer of the esophagus or stomach?

Overweight and obese individuals are two times more likely than healthy weight people to develop a type of esophageal cancer called esophageal adenocarcinoma. A smaller increase in risk has been found for gastric cardia cancer, a type of stomach cancer that begins in the area of the stomach next to the esophagus. Most studies have not observed increases in risk with obesity in another type of esophageal cancer, squamous cell cancer. An increased risk of esophageal adenocarcinoma has also been associated with weight gain, smoking, and being younger than age 59.

The mechanisms by which obesity increases risk of adenocarcinoma of the esophagus and gastric cardia are not well understood. One of the leading mechanisms proposed has been that increases in gastric reflux due to obesity may increase risk. However, in the few studies that have examined this issue, risk associated with BMI was similar for those with and without gastric reflux.

11. Does obesity increase the risk of prostate cancer?

Of the more than 35 studies on prostate cancer risk, most conclude that there is no association with obesity. Some report that obese men are at higher risk than men of healthy weight, particularly for more aggressive tumors. One study found an increased risk among men with high waist-to-hip ratios, suggesting that abdominal fat may be a more appropriate measure of body size in relation to prostate cancer.

Studies examining BMI and prostate cancer mortality have had conflicting results.

Despite the lack of association between obesity and prostate cancer incidence, a number of studies have examined potential biological factors that are related to obesity, such as insulin-related growth factors, leptin, and other hormones. Results of these studies are inconsistent, but generally, risk has been linked to men with higher levels of leptin, insulin, and IGF-1 (insulin-like growth factor-1).

12. Is there any evidence that obesity is linked to cancer of the gallbladder, ovaries, or pancreas?

An increased risk of gallbladder cancer has been found to be associated with obesity, particularly among women. This may be due to the higher frequency of gallstones in obese individuals, as gallstones are considered a strong risk factor for gallbladder cancer. However, there is not enough evidence to draw firm conclusions.

It is unclear whether obesity affects ovarian cancer risk. Some studies report an increased risk among obese women, whereas others have found no association. A recent report found an increased risk in women who were overweight or obese in adolescence or young adulthood; no increased risk was found in older obese women.

Studies evaluating the relationship between obesity and pancreatic cancer have been inconsistent. One recent study found that obesity increases the risk of pancreatic cancer only among those who are not physically active. A recent meta-analysis reported that obese people may have a 19 percent higher risk of pancreatic cancer than those with a healthy BMI. The results, however, were not conclusive.

13. Does avoiding weight gain decrease the risk of cancer?

The most conclusive way to test if avoiding weight gain will decrease the risk of cancer is through a controlled clinical trial. At present, there have been no controlled clinical trials on the effect on cancer related to avoiding weight gain. However, many observational studies have shown that avoiding weight gain lowers the risk of cancers of the colon, breast (postmenopausal), endometrium, kidney, and esophagus. There is limited evidence for thyroid cancers, and no substantial evidence for all other cancers.

14. Does losing weight lower the risk of cancer?

There is insufficient evidence that intentional weight loss will affect cancer risk for any cancer. A very limited number of observational studies have examined the effect of weight loss, and a few found some decreased risk for breast cancer among women who have lost weight. However, most of these studies have not been able to evaluate whether the weight loss was intentional or related to other health problems.

One recent study that examined the effect of intentional weight loss found that women who experienced intentional weight loss of 20 or more pounds and were not currently overweight had cancer rates at the level of healthy women who never lost weight. However, unintentional weight loss episodes were not associated with decreased cancer risk.

15. Does regular physical activity lower the risk of cancer?

There have been no controlled clinical trials on the effect of regular physical activity on the risk of developing cancer. However, observational studies have examined the possible association between physical activity and a lower risk of developing colon or breast cancer:

Colon cancer: In 2002, a major review of observational trials found that physical activity reduced colon cancer risk by 50 percent. This risk reduction occurred even with moderate levels of physical activity. For example, one study showed that even moderate exercise, such as brisk walking for 3 to 4 hours per week, can lower colon cancer risk.

A limited number of studies have examined the effect of physical activity on colon cancer risk for both lean and obese people. Most of these studies have found a protective effect of physical activity across all levels of BMI.

Breast cancer: The pattern of the association between physical activity and breast cancer risk is somewhat different. Most studies on breast cancer have focused on postmenopausal women. A recent study from the Women's Health Initiative found that physical activity among postmenopausal women at a level of walking about 30 minutes per day was associated with a 20 percent reduction in breast cancer risk. However, this reduction in risk was greatest among women who were of normal weight. For these women, physical activity was associated with a 37 percent decrease in risk. The protective effect of physical activity was not found among overweight or obese women.

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