Birth control pills could increase the risk of the most common type of stroke, according to a recent study.

Researchers from Loyola University Health System found that for healthy young women without any stroke risk factors, the risk of stroke associated with oral contraceptives is small. But in women with other stroke risk factors this risk is higher and significant, UPI reported.

More than 100 million women worldwide currently use oral contraceptives or have used them in the past. In the United States, there are about 40 brands of oral contraceptives and 21 brands of emergency contraceptive pills.

Researchers revealed that strokes associated with oral contraceptives were first reported in 1962.

Oral contraceptives increase the risk of ischemic strokes, which are caused by blood clots and account for about 85 percent of all strokes. In the general population, oral contraceptives do not appear to increase the risk of hemorrhagic strokes, which are caused by bleeding in the brain.

Researchers found that there are about 4.4 ischemic strokes for every 100,000 women of childbearing age. Birth control pills increase the risk 1.9 times, to 8.5 strokes per 100,000 women, according to a well-performed "meta-analysis" cited in the report, Softpedia reported. This is still a small risk; 24,000 women would have to take birth control pills to cause one additional stroke, according to the report.

They found that for women who take birth control pills and also smoke, have high blood pressure or have a history of migraine headaches, the stroke risk is significantly higher. Such women should be discouraged from using oral contraceptives, according to researchers.

The findings are detailed in the journal Medlink Neurology.