Study: Non-O Blood Type May Increase Stroke Risk Among Women Who Smoke, Take Oral Contraceptives

Preliminary research found that non-O blood type (A, B, or AB) may increase the risk of stroke among women who smoke and take oral contraceptives, according to research set to be presented at the American Stroke Association’s International Stroke Conference 2021, taking place virtually from March 17-19, 2021.

Some risk factors for stroke, such as older age and family history, cannot be controlled. Fortunately, several risk factors can be controlled, including not smoking, maintaining a healthy body weight, eating a healthy diet, being physically active, controlling high cholesterol and diabetes, and avoiding excessive alcohol use, according to the study authors.

In addition, oral contraceptives can also increase the risk of stroke in some women, especially those who smoke. Due to this risk, women who smoke and are older than 35 years of age should not take oral contraceptives, as previous research has shown that blood types, specifically non-O, also may increase the risk of stroke, according to the authors of the current study.

“We sought to determine whether blood group, specifically non-O blood group, increases the risk for stroke among oral contraceptive users,” said study lead author Steven J. Kittner, MD, professor of neurology at the University of Maryland School of Medicine in Baltimore, Maryland, in a press release. “The results of our small study suggest that this might be the case, but more data from other studies are needed to support or refute our findings. We did find that smoking markedly increased the risk of stroke in young women, regardless of oral contraceptive use, and this finding has been supported by numerous other studies.”

Using information from another study of early-onset stroke, the researchers compared the risk of stroke among women who smoked and used oral contraceptives, alongside a second analysis of women who only smoked or only took contraceptives. The study participants included 347 women who had experienced a stroke before 50 years of age, and a comparison group of 383 women without a stroke.

Additionally, the average age in both groups was 42 years, and approximately half of the patients were African American and half were white. All the participants lived in the Baltimore-Washington, DC, area and were enrolled in the Genetics of Early-onset Stroke study conducted at the University of Maryland School of Medicine between 1992 and 1996 or 2001 and 2003, according to the authors of the current study.

The research team found that women who both smoked and took oral contraceptives were nearly 5 times as likely to have a stroke compared to women who did not smoke or take oral contraceptives. Further, non-O blood type further increased the risk of early-onset stroke among women who both smoked and took oral contraceptives. Compared to women with O type blood who did not smoke and did not take oral contraceptives, those with non-O type blood who did both were nearly twice as likely to have a stroke.

These findings persisted after adjusting for other factors, including race, age, high blood pressure, diabetes, and migraine headaches. Blood type did not significantly affect stroke risk among women who either smoked only or took oral contraceptives only.

Women who smoked only were 3 times more likely to have a stroke than those who did not smoke, whereas women who took oral contraceptives only were nearly 4 times more likely to have a stroke compared to those who did not, according to the study authors.

“Women should follow established safety guidelines for the use of oral contraceptives, which recommend caution or non-use for women at higher risk for blood-vessel disease,” Kittner said in a press release. “Our study is intended to provide preliminary evidence for a hypothesis related to non-O blood group that will need to be confirmed; it does not present a finding that should be acted upon now.”

REFERENCE

Non-O blood type may increase stroke risk among women who smoke, take oral contraceptives. American Heart Association. https://newsroom.heart.org/news/non-o-blood-type-may-increase-stroke-risk-among-women-who-smoke-take-oral-contraceptives?preview=e13d. Published March 11, 2021. Accessed March 12, 2021.