AICR's expert report shows that physical activity lowers the risk of several cancers, both independently and by preventing weight gain. Yet if activity can help prevent cancer, can inactivity increase the risk? It's quite possible, suggests the emerging field of sedentary behavior.
Recent studies suggest that sitting for prolonged periods of time leads to unique physiological effects – independent of a person's structured activity time – that play a role in cancer and other chronic diseases. The research is still in its early phases, experts say, yet it may soon change the traditional view of healthy activity.
"There has been an explosion of research in [sedentary behavior] and health, and the preliminary evidence is pretty encouraging to make us think this is an important area of work to focus on for cancer risk," said Brigid Lynch, PhD, an epidemiologist at Canada's Alberta Health Services and author of a review on cancer risk and sedentary behavior.
"People who are active are getting health benefits of physical activity, and that's great, but what the research is finding is that it's not enough. We need to think about how people are spending the bulk of their day."
One of the first series of animal studies providing evidence that prolonged inactivity can lead to harmful physiologic effects came from findings with lipoprotein lipase (LPL), a protein produced in fat cells that plays a key role in cholesterol and other metabolic risk factors. "LPL, triglyceride metabolism and HDL are some of the most sensitive responses to inactivity we see," said Marc Hamilton, PhD, an inactivity physiologist at Pennington Biomedical Research Center and one of the leading scientists on the physiological effects of inactivity. Much of the data stem from animals, where scientists can clearly measure and control inactivity. The research has recently expanded to humans.
In one study, Hamilton and his colleagues found that fit men and women at a healthy weight experienced altered insulin action after only one day of inactivity. The participants acted as their own controls, sitting for long stretches at a time over one 24-hour period; sitting the same amount and eating more over a second 24-hour period; and moving about over the third 24-hour trial. Insulin activity was measured by giving participants an infusion of glucose after each trial.
"The [effect] appears to be something that doesn't take weeks or months or years to kick in, and that means that's independent of altering body fat," said Hamilton. Hamilton and his colleagues have also identified dozens of genes in our muscles whose expression depends upon activity or inactivity. The goal now is to show a clear cause and effect, he says.
In order to measure sedentary habits, researchers commonly ask study participants the amount of TV they watched and/or their occupation. Screen time, the amount of time people spend looking at their computer, watching TV or playing online games– is becoming a standard measure of sedentary behavior.
Advances in accelerometers, devices that measure movement, have also led to more affordable and accurate measures of activity levels, says Christine Friedenreich, PhD, Senior Research Scientist at Alberta Health Services-Cancer Care and part of the program committee for AICR's upcoming Research Conference.
The compelling data on sedentary behavior "has absolutely changed the way I do my research," says Friedenreich. Her research on physical activity and cancer risk now incorporates measurements of sedentary behavior as well as physical activity. Last year, for example, Friedenreich's study looking at lifetime physical activity found that endometrial cancer risk increased with sedentary occupational activity by 28 percent.
Excerpted from ScienceNow.
AICR's 2011 Research Conference will include a session on sedentary behavior. Early registration is now open.
Millions of Americans are eating fewer fruits and vegetables and exercising less compared to this same time last year, according to a new Gallup poll released last week, with Hispanics and young adults showing the greatest decrease in healthy habits compared to other demographics.
The poll found that the 55.9 percent of Americans reported eating five or more serving of fruits or vegetables at least four days in a week in May of this year. In 2010 that figure polled in at 57.8 percent. (According to a report from the Centers for Disease Control and Prevention, in 2009 approximately two-thirds of adults ate less than two fruits daily; almost three quarters of Americans ate vegetables less than three times daily.)
The percent of respondents who reported exercising at least 30 minutes at least three days a week in May dipped almost one percentage point over the past year. The percent of people eating healthy dropped two percentage points. According to the poll, the data revealed that about 4.5 million fewer American adults ate healthy in May this year than did in the same month one year ago.
People who follow cancer prevention guidelines on weight, nutrition and physical activity lower their risk of dying from cancer, but they also lower the risk of dying from heart disease and premature death in general, suggests a new study published in Cancer Epidemiology Biomarkers & Prevention.
The study used data collected from approximately 112,000 nonsmokers who were part of a large nutrition study. The participants, ages 50 to 74 at the start of that study, answered questions on diet, lifestyle, and weight. Researchers in the current study analyzed participants' adherence to a set of cancer prevention guidelines, which included recommendations on maintaining a healthy weight, being active, eating a plant-based diet and limiting alcohol consumption.
After 14 years of follow-up, the study found that both men and women who followed the cancer prevention guidelines most closely were 42 percent less likely to die of all causes during the course of the study than those who least followed the guidelines. (Only 4 percent of women and 3.5 percent of men met the optimal measure for each recommendation.) Those who most stuck to the guidelines were overall about half as likely to die from cardiovascular disease as those who did not– women were less likely to die than men. Maintaining a healthy weight was most strongly linked with cardiovascular lower death but all lifestyle factors contributed.
Cancer mortality was also lower among those who most followed the recommendations.
Source: McCullough ML, Patel AV, Kushi LH, Patel R, Willett WC, Doyle C, Thun MJ, Gapstur SM. "Following cancer prevention guidelines reduces risk of cancer, cardiovascular disease, and all-cause mortality." Cancer Epidemiol Biomarkers Prev. 2011 Jun; 20(6):1089-97.
Adding to a growing body of research on cancer survivorship and physical activity, a new study suggests that walking briskly and regularly may delay the progression of prostate cancer. The study is published in the June issue of Cancer Research.
Earlier this year, this same group of researchers found that activity after diagnosis reduced disease-related mortality in men with a certain type of prostate cancer. This new study focused on the effect of physical activity after diagnosis on early indicators of disease progression, such as a rise in PSA blood levels, along with treatment type, recurrence, and metastasis.
The study analyzed data from 1,455 men who were part of a nationwide prostate cancer registry study. Every six months the men filled out questionnaires on their health, then in 2004-2005 they answered questions on their activity habits over the past year. The median time from diagnosis to the activity questionnaire was slightly over two years.
After another two years of follow-up, the study found that men who walked at least three miles per hour – which the authors define as briskly – for at least three hours per week had a 57 percent lower rate of progression than men who walked at a slower pace for fewer than three hours weekly. Even men who walked briskly less than three hours per week had a lower risk of progression compared to the slower walkers.
As the authors note, the results are based on a relatively small number of brisk walkers and more studies are needed.
Source: Richman EL et al. "Physical activity after diagnosis and risk of prostate cancer progression: data from the cancer of the prostate strategic urologic research endeavor." Cancer Res. 2011 Jun 1;71(11):3889-95.
Research has provided conflicting evidence if the ubiquitous small-size snack packs actually help people eat less. Now a small study finds that the 100-calorie packages may especially help overweight people eat less, although it may not help people be more aware of how much they are eating.
In the guise of eliciting opinions about a television show, researchers offered 37 participants bowls of crackers to eat while watching the program. Participants watched the program in groups of four to five. Researchers randomly offered groups either one large 400-calorie package of crackers or a similar-sized package that was divided into four smaller 100-calorie crackers. The number of crackers was identical for everyone.
On average, participants ate a quarter fewer crackers when given the smaller 100-calorie packs compared to the one larger package. It was the overweight participants who were responsible for most of this effect, eating about half fewer crackers. There was no difference in consumption between package conditions among the normal-weight participants.
But whatever cracker package participants were offered, all participants underestimated how many crackers they actually ate by 60 percent or more.
Brian Wansink, Collin R. Payne and Mitsuru Shimizu. "The 100-Calorie Semi-Solution: Sub-Packaging Most Reduces Intake Among The Heaviest." Obesity 19, 1098-1100 (May 2011).