Monthly Archives: May 2016
This is the most comprehensive look so far at how physical activity influences cancer risk :
You know the virtues of regular physical activity: it can lower your risk of becoming overweight and can keep diseases like heart problems and diabetes at bay. But can it help reduce the risk of cancer, too? A new study published in JAMA Internal Medicine sheds new light on that question.
Previous studies have found that people who are more active tend to have lower rates of colon, breast and endometrial cancer. Exercise might lower colon tumors by speeding the transit of waste through the intestines, leaving little time for any potential cancer-causing agents to harm intestinal tissues. And physical activity can lower estrogen levels, which are known to contribute to breast and endometrial tumors. Still, there was plenty scientists didn’t fully understand about the mechanism, if there is one, by which exercise cuts down on cancer risk.
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In an effort to get a more complete picture of how exercise and cancer interact, a team led by Steven Moore, a cancer epidemiologist at the National Cancer Institute, took on the ambitious task of pooling data from 1. 4 million people who reported on their physical activity levels over a period of 11 years. Moore matched these peoples’ exercise records with whether they developed 26 different types of cancer.
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The data came from 12 different studies that looked at a wide range of the U.S. and European populations. Overall, people who exercising more saw a 7% lower risk of developing any type of cancer than people who exercised less. But the reduced risk was especially striking for 13 types of cancers. People who were more active had on average a 20% lower risk of cancers of the esophagus, lung, kidney, stomach, endometrium and others compared with people who were less active. The reduction was slightly lower for colon, bladder, and breast cancers.
“Everybody knows physical activity reduces heart disease risk,” says Moore. “The takeaway here is that physical activity might reduce the risk of cancers as well. Cancer is a very feared disease, but if people understand that physical activity can influence their risk for cancer, then that might provide yet one more motivating factor to become active.”
MORE: What If Your Immune System Could Be Taught to Kill Cancer?
Moore says that the relationship between physical activity and power cancer risk remained strong even after adjusting for other potential factors that could account for the reduction, including things like body mass index (BMI), diet and whether or not they smoked. While the reason for exercise’s benefit in lowering risk of these cancers isn’t clear, it’s possible that physical activity can shift insulin and inflammation to more beneficial levels that don’t promote tumor formation.
Two types of cancers, melanoma and prostate cancer, were higher among those who were more active. The skin cancer risk could be because people who exercise more may spend more time outdoors. The prostate cancer connection may be more complicated. Men who are more active may also pay more attention to their health overall, and therefore get screened more regularly for prostate cancer. (Many prostate cancers are not aggressive and do not require treatment.)
Moore adds the caveat that while the data are striking, and the sheer number of people involved gives the results some validity, the association still needs to be confirmed with more studies. For one, the people self-reported on their physical activity, and while the researchers asked them to include only moderate to vigorous exercise, there could still be some bias in how the people recorded their exercise levels. And while they accounted for major factors that could influence cancer outcomes, they might not have included all potential confounders. Even adjusting for BMI, for example, was tricky, since exercise can affect BMI since it affects weight, and people who are heavier tend to be less active.
Still, he says, the study is the most comprehensive look so far at how physical activity can influence cancer risk, and offers another potential way for people to lower their risk of the disease.
The list of cancer-causing agents is long and getting-longer. Experts already tell us to avoid smoking, exposure to UV radiation from the sun and even air pollution because these can increase the risk-of-cancer.
Now the World Health Organization says that hot drinks like coffee, tea and maté belong on that list too. The group’s International Agency for Research on Cancer (IARC), made up of 23 scientists from 10 countries, reviewed around 1,000 studies that investigated a connection between high-temperature beverages and their potential link to cancer. Based on the available evidence, they conclude that drinking very hot beverages, which they defined as anything above 149F (65C)—cooler than a cup of coffee from most take-out spots—is linked to higher risk of cancer of the esophagus.
They based their conclusion, which is published in Lancet Oncology, on studies that found higher rates of esophageal cancer among people who drank extremely hot tea or coffee compared to those who consumed their drinks at lower temperatures. The link to cancer remained strong even after they adjusted for things like smoking and other possible cancer risk factors. Animal studies also seem to hint that even very hot water can increase the risk of this type of cancer, presumably because the temperature scalds delicate tissues in the esophagus; that damage may then trigger more rapid turnover of the cells, which can in some cases lead to out-of-control malignant growth.
The group of probable cancer-causing agents in people includes 79 substances, most recently red and processed meat, fried foods, DDT and the human papillomavirus (which is linked to cervical cancer).
The report also concludes, however, that there isn’t adequate evidence to classify coffee itself as a carcinogen. That’s a downgrading of the risk for coffee from its previous analysis, done in 1991, when studies linking coffee consumption to a higher risk of bladder cancer led the IARC to deem coffee as “possibly” carcinogenic to people. Now, says Dana Loomis, deputy head of the IARC, “the available scientific evidence base is much larger and stronger. There are quality studies available today that are significantly better than those in 1991.” Recently, more studies that control for such factors support the benefits of coffee in lowering risk of cancer in certain parts of the body. But for 20 other types of cancer, the evidence isn’t strong enough to suggest either a benefit or risk, so the IARC is changing the designation to “inadequate evidence for carcinogenicity of coffee drinking overall.”
That seems to contradict the finding about hot beverages, since most people drink their coffee hot. But the classifications aren’t necessarily mutually exclusive. People who drink more coffee seem to have lower rates of certain cancers, including liver and endometrial cancers. But, says Dr. Otis Brawley, chief medical and scientific officer at the American Cancer Society, “that’s not where hot beverages hit. Hot beverages hit the mouth, throat, esophagus and stomach.” So that means that even though coffee may be hot, as long as it’s not too hot, there doesn’t seem to be evidence linking coffee to higher risks of cancer other than esophageal cancer.
In the studies the group reviewed, there seemed to be an increased risk of esophageal cancer only when people drank very hot beverages, usually above 149F. The National Coffee Association USA recommends holding coffee at 180 to 185F; most coffee sellers serve their drinks at about 10 degrees below that after a lawsuit by a customer who was scalded by cup at the holding temperature at McDonald’s—but that’s still higher than experts now recommend to avoid cancer risk.
The people who might want to discuss the latest classification change with their doctors are people with Barrett’s esophagus, a condition that often precedes esophageal cancer. For almost every else, says Brawley, the risk from the higher temperature drinks is much smaller than the risk from other, more common risk behaviors. “I would say anybody who drinks alcohol shouldn’t even worry about this because alcohol is far more of a cancer-causer than coffee or hot drinks. Anybody who smokes cigarettes also shouldn’t worry about this because cigarettes are a far greater cause of cancer than alcohol.”
“Basically this is a reassuring message for coffee drinkers,” says Dr. Alberto Ascherio, professor of nutrition and epidemiology at Harvard T. H. Chan School of Public Health. Just don’t drink it too hot.