Weight and physical activity levels may affect the risk of a certain brain cancers, new research suggests.
Excess weight was associated with a higher risk of a type of brain cancer known as meningioma. Obesity increased the risk of meningioma by 54 percent, and being overweight upped the risk by 21 percent, the study found.
On the other hand, people who were physically active reduced the risk of meningioma by 27 percent, the researchers said.
"There are very few known preventive factors for these tumors," said study author Gundula Behrens, from the department of epidemiology and preventive medicine at the University of Regensburg in Germany. "According to our study, reducing excess weight and adopting a physically active lifestyle may help prevent meningiomas."
The study also found that being heavier was not linked to the risk of a second, deadlier form of brain cancer called glioma. And while there was a weak association between more physical activity and a lower risk of glioma, the researchers said the finding wasn't statistically significant.
While the study was able to show an association between weight and physical activity and the risk of meningioma, it wasn't designed to prove a cause-and-effect relationship.
The findings were published online Sept. 16 in Neurology.
Meningioma and glioma are the most common types of brain tumors in adults, according to background information in the study. However, these tumors are still rare.
Annually, about five to eight people of every 100,000 will be diagnosed with meningioma. About five to seven of every 100,000 people will receive a glioma diagnosis in a given year, the study authors said.
At five years following a diagnosis, 63 percent of people with meningioma will still be alive. Glioma is far more deadly, with only a 4 percent survival rate at five years, the study reported.
Dr. Gowriharan Thaiyananthan, a neurosurgeon at the Brain and Spine Institute of California in Newport Beach, said, "The absolute risk of development of either a meningioma or glioma is small, but there seems to be a positive correlation with a slightly increased risk of developing meningiomas with obesity.
"Exercise and loss of weight may help obese individuals decrease their risk of developing meningiomas," said Thaiyananthan, who was not involved with the study.
The current research was a review of 18 previous studies involving more than 6,000 people. About half the patients had meningiomas, and the other half had gliomas.
Some of the studies compared patients with healthy counterparts. Twelve of the studies looked at body mass index and cancer risk, and six looked at physical activity and cancer risk.
The studies defined obesity as a body mass index (BMI) over 30 and overweight as a BMI from 25 to 29.9. Body mass index is a measurement that provides a rough estimate of body fat based on height and weight. Physical exercise was rated as high or low in the studies.
In addition to effects of weight and exercise on meningioma risk, the study authors found a 32 percent reduced glioma risk among underweight teens (BMI less than 18.5).
How excess weight or physical activity might affect the development of certain brain tumors is unclear. One possible explanation, the study authors said, is that people with excess weight produce excess estrogen, and estrogens promote meningioma development. Insulin levels could be a factor for the same reason, the authors speculated.
The relationship between meningioma risk and exercise may be more complicated. Behrens and her co-authors noted that brain tumor symptoms could have led some patients to reduce their normal physical activity even before their diagnosis. These patients might have reported low activity levels because their brain cancer slowed them down before they knew they had it, the researchers said.
Can someone who is already overweight or obese do anything to take advantage of this information? Thaiyananthan thinks so. "It's plausible that exercise and weight reduction may help prevent the meningioma formation in persons already at risk for these tumors," he said.