Cancers Caused by Lifestyle Behaviors: Experts Urge Action

World Cancer Report 2014


The World Cancer Report 2014 was recently launched and highlighted lifestyle behaviors that lead to cancer, including smoking tobacco, overweight/obesity, and lack of exercise. Prevention of cancer is key, say the experts.

The report, issued by the International Agency for Research on Cancer (IACR), contains contributions from more than 250 scientists worldwide, many of them leading experts in their fields.   It offers a "timely update," said Margaret Chan, MD, director-general of the World Health Organization (WHO). The report compiles the most up-to-date analysis of data on all aspects of cancer, and among the evidence presented are data showing the extent to which lifestyle behaviors contribute to cancer.

The American Society of Clinical Oncology (ASCO) called for action in response to the report, highlighting a "need to deepen the global commitment to cancer prevention."

"Decades of research have shown that cutting tobacco use is the single most powerful way to prevent many deadly cancers, especially in developing countries where smoking is most widespread. Tackling obesity, a key modifiable risk factor for many cancers, is another top prevention priority," ASCO said in a statement. In the United States, 1 in 3 cancer deaths is related to obesity, poor nutrition, or physical inactivity, and the problem will only increase as more countries and regions adopt the diet and lifestyles of more economically developed economies."

Tobacco Is Still Most Important

Tobacco, both smoked and smokeless, remains the world's leading cause of cancer morbidity and mortality, the report notes.  Nearly 20% of the world's adult population smokes, and worldwide tobacco is killing around 6 million people each year from a variety of smoking-related diseases, the report estimates.

The IACR and also the US Surgeon General have concluded that the relationship with smoking is causal for cancers of the nasal and oral cavities, hypopharynx, larynx, trachea, esophagus, lung, bronchus, bone marrow (leukemia), stomach, kidney, pancreas, ureter, uterus, bladder, and cervix. The IACR expands this list to also include paranasal sinuses, liver, colon, rectum, and ovary (mucinous), but says it is unclear if there is a link with breast cancer.

The good news here is that tobacco is now recognized as damaging to health, and control strategies are being introduced globally, backed by the WHO Framework Convention for Tobacco Control (in place since 2005).

Diet, Obesity, and Physical Activity

The IACR report says that additional research is needed on many aspects of diet and physical activity in relation to cancer, including the effects of these behaviors during childhood and early adulthood.

Nevertheless, it draws several conclusions, as follows:

  • Excess body fat increases the risk for cancers of the esophagus, colon, pancreas, endometrium, and kidney, as well as postmenopausal breast cancer. The evidence for obesity increasing the risk for these cancers is "convincing," the agency comments, and there is a dose–response relationship, so being overweight is less risky than being obese.
  • Regular physical activity reduces the risk for multiple cancers by contributing to weight control, and also reduces the risk for colorectal and breast cancer by additional mechanisms. The general consensus among researchers is that exercise should be of moderate intensity and average at least an hour each day.
  • High consumption of red meat, especially processed meat, is associated with a risk for colorectal cancer.

"A diet high in fruit and vegetables and whole grains does not appear to be as strongly protective against cancer as initially believed," the report notes. "However, this dietary pattern is still advisable because of the benefits for diabetes and cardiovascular diseases, and some possible reductions in cancer incidence."

In an invited commentary in the report, Walter Willet, MD, professor of epidemiology and nutrition at the Harvard School of Public Health and professor of medicine at Harvard Medical School in Boston, says the evidence for overweight, obesity, and physical inactivity contributing to cancer is now "sufficiently strong to support strong actions to reduce these hazards."  "Although the risks of cancer are for an individual who is overweight or obese are not as great as they are for a tobacco smoker, in the United States and some other countries, the much higher prevalence of overweight and obesity than smoking means that the numbers of cancer deaths caused by these 2 factors are now similar," he comments.

"Control of overweight and obesity must be a high priority for cancer prevention," Dr. Willet comments. These efforts should be closely integrated with those for the prevention of other diseases, such as cardiovascular disease and type 2 diabetes, he adds.

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