Studies Reaffirm That Healthy Behaviors Can Cut Cancer Risk

Roxanne Nelson

January 12, 2015

As people make their resolutions for 2015, two new studies — which show that curbing alcohol consumption, adding more plant foods to the diet, and losing excess weight can help reduce the risk of developing cancer — serve as a reminder that a healthy lifestyle is important.

The first study, published online January 6 in Cancer Causes & Control, showed that eating a plant-based diet and limiting alcohol intake, both already included in various cancer prevention guidelines, could help cut the risk for obesity-related cancers (about a third of all of cancers).

In a cohort of nearly 3000 adults, the researchers found that restricting alcohol consumption to one drink per day for women and two drinks per day for men was associated with 29% reduced risk for obesity-related cancers. Additionally, the risk was up to 71% lower for the most common site-specific cancers in the United States (breast, prostate, and colorectal).

For individuals who consume starchy vegetables, such as corn, potatoes, and yams, sufficient consumption of nonstarchy legumes, fruits, and vegetables was associated with a reduction in the risk for colorectal cancer.

"These results add to the existing evidence on the potential role of limiting alcohol intake and increasing the intake of plant foods in influencing cancer risk," said lead author Nour Makarem, a nutrition doctoral student at New York University's Steinhardt School of Culture, Education, and Human Development. "Therefore, based on these results, dietary advice on cancer should focus on encouraging the consumption of a plant-based diet providing abundant nonstarchy fruits, vegetables, and legumes, and restricting alcohol, if consumed at all, to the recommended levels."

In 1997, the World Cancer Research Fund (WCRF) and the American Institute for Cancer Research (AICR) issued cancer prevention guidelines for weight management, diet, and physical activity. These were updated in 2007 and are considered to be the most comprehensive scientific analysis of cancer prevention and causation ever undertaken. Specifically, the guidelines reported that excess body fat is associated with an increased cancer risk and that there is convincing evidence that the consumption of alcohol, red meat, and processed meat elevates cancer risk.

Since that time, numerous studies have reported links between colorectal cancer risk and alcohol, between breast cancer mortality and obesity, between breast cancer relapse and obesity, and between breast cancer risk and red meat.

"It is important to keep in mind that the evidence for the development of the WCRF/AICR guidelines for cancer prevention was based on a comprehensive evaluation of relevant individual scientific studies that addressed one or more foods, food groups, and behaviors in relation to cancer risk," Makarem told Medscape Medical News. "Therefore, individuals, especially those at high risk of cancer, should be advised to adhere to all cancer prevention guidelines to reduce their risk."

Pronounced Effect on Cancer Risk

In their study, Makarem and colleagues investigated whether the healthful behaviors outlined in the WCRF/AICR guidelines were associated with the risk for obesity-related cancers, in particular, breast, prostate, and colorectal cancer.

Of the 2983 adults enrolled in the Framingham Offspring cohort from 1991 to 2008, the researchers identified 480 incident obesity-related cancers.

Data from food frequency questionnaires, anthropometric measures, and self-reported physical activity were used to develop a 7-component score based on recommendations for body fatness; physical activity; foods that promote weight gain; plant foods; animal foods; alcohol; and food preservation, processing, and preparation.

The cohort was, on average, middle aged to older and overweight, but had a relatively high level of physical activity. The mean duration of follow-up was 11.5 years.

The overall score was not associated with obesity-related cancer risk after adjustment for confounders such as age, sex, smoking, energy, and pre-existing conditions (hazard ratio [HR], 0.94; 95% confidence interval [CI], 0.86 - 1.02).

However, when the score components were considered separately, the researchers found that for every unit increment in the alcohol score (representing an improvement and more closely meeting the guideline recommendations), there was 29% lower risk for obesity-related cancers (HR, 0.71; 95 % CI, 0.51 - 0.99) and a 49% to 71% reduced risk for breast, prostate, and colorectal cancers.

Similarly, each unit increment in the subcomponent score for nonstarchy plant foods (fruits, vegetables, and legumes) for those who eat starchy vegetables was associated with a 66% lower risk for colorectal cancer (HR, 0.44; 95% CI, 0.22 - 0.88).

"The message on the importance of lifestyle — namely diet and physical activity — in cancer risk can be most effective by targeting individuals, the physical and social environment, and policy at the government level," explained Makarem. "At the individual level, clinicians providing dietary advice on cancer should emphasize the importance of adequate consumption of nonstarchy plant foods, especially among patients who consume starchy vegetables, and of restricting alcohol consumption to the recommended amounts."

She added that "public health and policy initiatives to reduce alcohol consumption and promote a plant-based diet — by increasing availability, affordability, and access to healthy plant foods through healthy grocery stores and supermarkets, green carts, and farmers markets — may also help reduce the cancer burden."

Healthy Body Weight and Exercise Reduce Mortality

The second study, published online January 7 in the American Journal of Clinical Nutrition, reported similar results. Researchers found that greater adherence to the cancer prevention guidelines of the American Cancer Society (ACS) was associated with a reduction not only in cancer incidence, but also in cancer mortality and total mortality.

The ACS guidelines recommend that individuals avoid smoking, achieve and maintain a healthy weight, be physically active, and eat a healthy diet that emphasizes plant foods.

In their study, Geoffrey Kabat, PhD, senior epidemiologist in the Department of Epidemiology & Population Health at the Albert Einstein College of Medicine in Bronx, New York, and colleagues report that maintaining a healthy body weight and being physically active had the greatest impact on overall mortality for both men and women.

The researchers used data from the NIH-AARP Diet and Health Study, a prospective cohort study of 566,401 adults who were 50 to 71 years of age in 1995 and 1996, when they enrolled in the study.

They were followed for a median of 10.5 years for cancer incidence, 12.6 years for cancer mortality, and 13.6 years for total mortality.

During the study period, there were 73,784 cases of cancer, 16,193 cancer deaths, and 81,433 deaths from any cause.

The patients were stratified by how closely they adhered to ACS guidelines, and adherence to the guidelines was associated with a reduced risk for all cancers combined. When the highest level of adherence was compared with the lowest level, the hazard ratio was 0.90 for men and 0.81 for women.

In addition, increased adherence was associated with a reduction in risk for 14 of 25 specific cancers. Reduction in the risk for gallbladder cancer was 65% in men and women combined, for endometrial cancer was 60%, for liver cancer was 48% in men, for colon cancer was 48% in men and 35% in women, and for rectal cancer was 40% in men and 36% in women.

"Our findings suggest that it's worth the effort to adhere to the ACS guidelines, and that the closer you follow the guidelines, the greater the benefit for preventing certain types of cancer," Dr Kabat said in a statement.

The authors have disclosed no relevant financial relationships.

Cancer Causes Control. Published online January 6, 2015. Abstract

Am J Clin Nutr. Published online January 7, 2015. Abstract

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