Compared to women who had never used an IUD, the international study found that those who had used the implanted contraceptive had almost half the risk for developing cervical cancer, which is caused by infection with the sexually transmitted human papilloma virus (HPV).
IUD use is known to reduce endometrial cancer risk. But the impact of the birth control method on cervical cancer and HPV infection has not been clear, says study researcher Xavier Castellsague, PhD, of Catalonia, Spain's Institut Castala d'Oncologia.
The study is published online The Lancet Oncology.
"The good news for IUD users is that this form of birth control does not increase the risk of HPV infection and it appears to lower the risk for developing cervical cancer," he tells WebMD.
Castellsague and colleagues analyzed data from 10 previously published studies that compared women with cervical cancer to women without the disease and 16 HPV frequency surveys conducted in 14 countries.
The researchers concluded that IUD use did not affect HPV infection risk. But IUD use reduces the risk for developing both major types of cervical cancer: squamous cell and adenosquamous carcinoma.
The risk for both cancers was found to be reduced by nearly half during the first year of IUD use. A similar level of protection was seen in women who had used the implanted birth control device for as long as a decade.
Why IUDs May Lower Cervical Cancer Risk
The researchers have several theories that may explain how the implanted contraceptive protects against cervical cancer.
IUDs are small, T-shaped plastic devices placed in the uterus by a health care professional to prevent fertilization and implantation of the egg. One type of IUD is wrapped in copper while another type contains a form of the hormone progestin.
One theory is that the procedure to insert or remove an IUD may destroy HPV-related lesions before they become cancerous. Another is that hormone-targeting IUDs affect the natural history of HPV infection.
It was not clear how many women in the studies used hormonal IUDs and how many used the copper-wrapped devices.
Castellsague says it is more likely that IUD-induced chronic, low-grade inflammation within the cervix could mobilize the immune system to fight HPV progression.
But the researcher says since cervical cancer is caused by persistent viral infection, inflammation may help the immune system keep HPV in check by blocking viral replication.
Strategies for Preventing Cervical Cancer
More than 100 million women across the globe use IUDs for birth control, but less than 1% of women in the U.S. use the devices.
American Cancer Society (ACS) senior epidemiologist Edgar P. Simard, PhD, says it remains to be seen if the protection is similar for copper IUDs and hormone-containing IUDs.
He adds that while the research should reassure women who use the contraceptive devices, IUD use is not likely to become a strategy for preventing cervical cancer in the U.S.
That's because two highly effective strategies -- Pap smear testing and vaccination against HPV -- are already widely used.
"Routine Pap smears have resulted in historical declines in cervical cancer and future declines may be attributed to HPV vaccination of girls during childhood," he says in a statement.
Simard says the findings should be confirmed in regions where both IUD use and cervical cancer are more common.
"Despite the importance of these results, routine cervical cancer screenings and HPV vaccination remain the most prudent methods of cervical cancer prevention," Simard notes.