Intrauterine devices may offer some protection against cervical cancer, a large review of studies has found.

The studies were conducted from 1985 to 2007 in Europe, Asia and South America and involved nearly 20,000 women. After controlling for many health and behavioral factors, the researchers found that using an IUD reduced the risk of cervical cancer by 45 percent, compared with never using one. The review, published online last week in Lancet Oncology, said the protective effect was apparent in the first year of use and continued for as many as 10 years.

Women who choose to have IUDs inserted are more likely to have been screened for cervical cancer, but the researchers found that screening was not a factor in the reduced risk. And women with IUDs were no more or less likely than women without them to be infected with human papillomavirus, the main cause of cervical cancer. Rather, the researchers suggest, the insertion of an IUD might provoke an immune response to HPV.

The data underscore two important points, according to the lead author, Dr. Xavier Castellsagué, an epidemiologist at the Catalan Institute of Oncology in Barcelona, Spain. First, having an IUD does not change the risk for HPV infection. And second, IUD use is associated with a reduction of almost 50 percent in the risk for cervical cancer.