Taking certain forms of birth control for over five years more than doubles the risk of developing a rare brain tumor, a study led by a Danish neurologist has found. 

The study, due to be published Thursday in the British Journal of Clinical Pharmacology, says that women who take hormonal contraceptives showed higher rates of glioma, a tumor that affects around five people in every 100,000. 

The study examined the contraception methods over 317 women with glioma aged 15 years to 49 years and compared them to a control group. The researchers found that those who used contraceptives containing only progestin for more than five years had a risk that was 2.4 times higher than the control group. Those who used other types of birth control saw their risk for glioma raised, but not quite as high. 

Overall, women who had used hormonal contraceptives at any point for any length of time had a 50 percent higher of developing the tumor than those who had not. 

Research team leader Dr. David Gaist says that he hopes the study would lead to further study on possible links between oral contraceptives and brain cancer. However, he also said that the study should not be taken as a reason to stop using birth control. 

"It is important to keep this apparent increase in risk in context," Dr. Gaist told The Daily Telegraph. "In a population of women in the reproductive age, including those who use hormonal contraceptives, you would anticipate seeing 5 in 100,000 people develop a glioma annually.

"While we found a statistically significant association between hormonal contraceptive use and glioma risk, a risk-benefit evaluation would still favour the use of hormonal contraceptives in eligible users.

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