Hormonal birth control methods are a routine part of many women's lives. And new evidence has tied them to a surprising condition.
A new Danish study tied long-term use of hormonal contraceptives to a slight increase in the risk of glioma, a type of brain tumor.
"It is important to keep this apparent increase in risk in context," said lead study author David Gaist, MD, PhD, of the Odense University Hospital in Denmark, in a press release. "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, according to the nationwide Danish Cancer Registry."
"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," Dr. Gaist said.
A glioma is a type of tumor that develops in cells surrounding nerve cells. Gliomas can appear in the brain and spinal cord. These tumors can vary in severity, but may require treatments like surgery or chemotherapy.
According to Dr. Gaist and team, gliomas are less common among women than men, suggesting that perhaps sex hormones play a roll. With this in mind, these researchers wanted to see whether use of hormonal methods of birth control could affect the risk of developing gliomas.
Hormonal contraceptives are a very common form of birth control that include the birth control pill, patch, injections and ring. These forms of birth control all use female sex hormones to prevent pregnancy.
Dr. Gaist and team looked at health registries in Denmark for the years 2000 to 2009. They studied more than 300 women between the ages of 15 and 49 who were diagnosed with a first-time glioma. They compared these cases to more than 2,000 similarly-aged females who had not been diagnosed with glioma.
After comparing the cases, Dr. Gaist and colleagues found a slight tie between the use of hormonal contraceptives and glioma risk.
Using hormonal birth control at any point was tied to a 1.5 times increased risk of developing glioma over women who didn't use hormonal birth control. When looking at women who had used hormonal birth control for a long time — five years or more — the risk was 1.9 times greater than among women who had never used hormonal contraceptives.
Dr. Gaist and team called for more research to explore the possible tie between hormonal birth control and brain tumors. Other factors could be involved, they noted.
This study was published Jan. 22 in the British Journal of Clinical Pharmacology.
A number of groups funded this research, such as the Danish Cancer Society and the University of Southern Denmark. Some of the study authors had research ties to pharmaceutical companies like Pfizer and Amgen.