Physical activity later in life didn't seem to matter, study finds
TUESDAY, Oct. 6 (HealthDay News) -- Exercising during adolescence may help guard against a deadly form of brain tumor in adulthood, new research suggests.
The study also found that avoiding obesity during the teen years was associated with a lower risk of developing the cancerous brain tumors called gliomas, while being tall increased the chances of such malignancies.
The study appears in the Nov. 1 issue of Cancer Research.
Gliomas are the most common type of brain and central nervous system cancers, accounting for 80 percent of cases, according to background information in the study. Gliomas cause 13,000 deaths in the United States each year.
Though little is known about why people develop the tumors or who is at risk, previous research has hinted that "early life exposures" may increase the risk of developing the cancer in adulthood, said study author Steven C. Moore, a research fellow in the Nutritional Epidemiology Branch of the U.S. National Cancer Institute. Studies have shown that people who are left-handed, for example, are at higher risk of the disease.
In the current research, Moore and his colleagues examined data on nearly 500,000 men and women aged 50 to 71 participating in the NIH-AARP Diet and Health Study, which included questionnaires on height and weight at various points during their lives.
Those who'd reported doing substantial amounts of light, moderate and vigorous exercise between the ages 15 and 18 were 36 percent less likely to develop glioma than those who were sedentary. Activities included walking, aerobics, biking, swimming, running, heavy housework or gardening.
The researchers also found that those who were obese during their teen years had a three to four times greater risk of developing glioma than those of a normal weight. Because only 11 people who developed glioma were also obese as teenagers, researchers said the finding needed to be replicated.
"The BMI [body mass index] finding is very interesting but it's hard to know what to make of it," Moore said. "It's also hard to say if it's a causal relationship or not. It could be that obesity increases the risk of brain cancer, or if could be that some underlying condition increases both the risk of obesity and brain cancer."
Neither weight nor exercise affected glioma risk beyond the teen years.
Tall people were also at increased risk of glioma. Each 10 centimeter (about 3.9 inches) increase in height meant a nearly 20 percent increase in risk of developing glioma.
The researchers said increases in glioma risk could be related to "energy balance" during a critical period of brain development. People who are tall have higher levels of the growth factor IGF-1 during childhood. Growth factors promote the proliferation of cells.
"Anything that increases the rate of proliferation of cells could potentially be a cancer risk factor," Moore said.
Dr. Paul Graham Fisher, a professor of neurology at Stanford University, said the study was "well done," but questioned why exercise and weight did not affect glioma risk beyond the teen years.
"You start scratching your head and asking, 'Why wouldn't it be true in the 20s and 30s or later?'" Fisher said. "It's possible there is some critical window in which energy balance can impact glioma genesis."
And though researchers relied on the recollections of older adults about their weight and physical activity from many decades ago, there's no reason to suspect people who were later diagnosed with glioma had any better or worse memories, or reported their height and weight with any particular bias than those who didn't develop the brain tumors.
With the risk of developing glioma so low among the general population, the findings aren't so much a prescription for teens to exercise as more information for researchers searching for the biological underpinnings of glioma in the hopes developing new treatments.
Yet it's not a bad idea to encourage teens to stay active, too, Moore said.
"At this point in time, these data are more relevant to the biology of glioma, but they provide some preliminary evidence that physical activity could be important for glioma, too," Moore said.
The U.S. National Cancer Institute has more on brain tumors.
SOURCES: Steven C. Moore, Ph.D., research fellow, National Cancer Institute, Rockville, Md.; Paul Graham Fisher, M.D., professor, neurology, Stanford University, Palo Alto, Calif.; Nov. 1, 2009, Cancer Research
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