In a new report published in the journal Neurology, it is suggested that being obese or overweight may contribute to the development of some types of brain tumor.
Malignant brain tumors are notoriously difficult to fight, and in most cases, the cause is unknown. Prior exposure to brain radiation has been suggested by the American Academy of Neurology (AAN) as the “most solid risk factor for developing a primary brain tumor,” and certain rare genetic conditions may increase the risk. But for many of the 120 plus different types of brain tumor, the origin remains a mystery.
The study, carried out by Gundula Behrens, PhD, of the University of Regensburg in Germany, focused on two types of brain tumor: meningioma and glioma – the most common primary tumors in adults.
Glioma accounts for about 33% of brain tumors. Gliomas originate in the glial cells in the brain. Glial cells are the tissue that surrounds and supports neurons in the brain.
Gliomas are called intrinsic brain tumors because they reside within the substance of the brain and often intermix with normal brain tissue.
Meningioma accounts for about 30% of brain tumors. The tumors develop in the meninges – the three layers of tissue that surround and protect the brain and spinal cord.
They are benign in 85% of cases, and tend to grow slowly, but can be dangerous and even fatal when they start to interfere with the functioning of the brain. A small number are malignant and fast-growing, metastatizing into the brain and lungs. Meningioma occurs at a rate of about 5-8 cases per 100,000, and has a 5-year survival rate of approximately 63%.
- 688,000 people in the US are living with a primary brain or central nervous system tumor
- 138,000 Americans are living with benign brain tumors
- 550,000 people in the US have malignant brain tumors.
Behrens carried out a meta-analysis of 18 studies, looking at all the available data on body mass index (BMI) and physical activity relating to 2,982 meningioma cases and 3,057 glioma cases.
Behrens found that overweight people (BMI of 25-29.9) were 21% more likely to develop a meningioma, and obese people (with a BMI of 30 or over) were 54% more likely to develop a meningioma, compared with people of “normal body weight” – a BMI below 24.9.
In addition, having a high level of physical activity was modestly associated with a lower risk of meningioma. Those who were the most physically active were 27% less likely to have a meningioma than those with the lowest amount of activity.
Behrens calls the link “an important finding” because there are few known risk factors for meningioma, and most of these are not within the individual’s control.
“Given the high prevalence of obesity and the unfavorable prognosis for this type of tumor, these findings may be relevant for strategies aimed at reducing the risk of meningioma.”
No relationship was found between excess weight and glioma, which occurs at about the same rate as meningioma but has a worse prognosis.
Behrens suggests several biological processes that might link excess weight to increased risk of meningioma.
Excess weight tends to imply a higher rate of production of estrogen, which is known to promote the development of meningioma. Also, excess weight is linked to high levels of insulin, which could also promote meningioma growth.
Behrens pointed out that while the analysis associates extra weight and lack of exercise with meningioma, it does not prove that this is the cause. She suggests that people suffering from meningiomas may have reduced their physical activity in the period before the tumor was diagnosed.
Behren’s analysis supports conclusions drawn by a 2008 study published in the British Journal of Cancer, which concluded that “the incidence of glioma or meningioma tumors increases with increasing height and increasing BMI.”