July 27, 2009 — A study from Finland has shown that men who exercised for at least 30 minutes a day at moderate to high intensity halved their risk of dying prematurely from cancer, mainly gastrointestinal and lung cancer.
The results were published online July 28, 2009 in the British Journal of Sports Medicine.
Physical inactivity over a person's lifespan might be a "key factor in the initiation of cancer development," the authors note.
This study adds ammunition to the public-health message promoting at least 30 minutes a day of exercise, lead author Sudhir Kurl MD, from the School of Public Health at the University of Kuopio in Finland, told Medscape Oncology.
All doctors should be giving their patients this message.
"All doctors should be giving their patients this message," he said, although he acknowledged that many do not have the time, and many are not aware of all of the research showing benefits.
"We found a 50% reduction in the risk of dying prematurely from cancer," Dr. Kurl pointed out. Exercise also improves well being and confidence, and leads to better sleep and weight control, he added.
The study was carried out in men, but Dr. Kurl said he expects to see similar results in women.
Intensity of Physical Activity Was Important
The study involved 2560 men, aged 42 to 60 years, living in the town of Kuopio and the surrounding rural communities. They self-reported their leisure-time physical activities on questionnaires over a period of 1 year, and were then followed for an average of 16.7 years, during which time there were 181 cancer-related deaths.
In their analysis, the researchers adjusted for age, cigarette smoking, alcohol consumption, body mass index, and total intake of calories, fat, and fiber.
The reduction in the risk for premature death from cancer was seen in men who exercised for more than 30 minutes every day, and with an intensity that was moderate to high, Dr. Kurl noted. The activities they performed included jogging, swimming, cycling to work, and gardening or yard work, he said
Exercise intensity was measured in metabolic equivalents of oxygen consumption (METs). The average intensity of jogging was 10.1 MET, of skiing was 9.6 MET, of ball games was 6.7 MET, of swimming was 5.4 MET, of rowing was 5.4 MET, of cycling was 5.1 MET, of gardening/farming/yard work was 4.3 MET, and of walking was 4.2 MET.
"Anything above an average of 4 MET can be considered [to be] moderate-intensity exercise," Dr. Kurl told Medscape Oncology.
Other activities reported by the men included crafts, repair or building, which had an average intensity of 2.7 MET, hunting, picking berries or gathering mushrooms (3.6 MET), and fishing (2.4 MET).
"The intensity of leisure-time physical activity should be at least moderate so that the beneficial effect of physical activity for reducing overall cancer mortality can be achieved," the authors write.
The results show that at least moderate-intensity physical activity is more beneficial than low-intensity physical activity in the prevention of cancer, the authors note. This finding is consistent with American consensus statements suggesting that at least moderate-intensity physical activity is needed to prevent chronic diseases caused mainly by cardiovascular disease, they add.
Several Mechanisms Involved
They speculate that the mechanisms by which physical activity could protect against cancer include beneficial effects on energy balance and body mass, intestinal transit time, hormonal concentrations (e.g., reduced testosterone), prostaglandin levels, and antioxidant enzymes activities.
For example, exercise increases the F-series of prostaglandinsbut decreases the E2 series, and these physiologic events have been shown to increase gut motility and to decrease colonic cell division, the researchers point out.
Many of the cancer-related deaths that were reported during the follow-up period affected the gastrointestinal tract (57 of 181 cases). The remaining cancers affected the lung (n = 48), prostate or urinary tract (n = 25), brain (n = 9), or lymphoma (n = 6).
"Our results indicate that those with an active lifestyle have a decreased risk of gastrointestinal cancers," the researchers note. This finding may be due to changes in energy balance, which includes body mass, which is particularly important for colon cancer, they note. In addition, the increased gut motility with exercise training decreases gastrointestinal transit time, thereby reducing the contact time between fecal carcinogens and the colonic mucosa, as well as allowing less opportunity for the initiation of carcinogenesis and colonic cell division and proliferation. There may also be an affect on insulin and fat metabolism, they add.
Asked by Medscape Oncology if he practices what he preaches, Dr. Kurl replied: "Of course!" He reported jogging 3 times a week and working out in the gym twice a week .
The researchers have disclosed no relevant financial relationships.
Br J Sports Med. Published online before print July 28, 2009.
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Cite this: Exercise Reduces Risk for Premature Death From Cancer - Medscape - Aug 03, 2009.