In a study, 52 women performed two stressful tasks -- a series of timed math problems, and making a speech defending their innocence after being falsely accused of wrongdoing, according to Davis, a researcher at Arizona State University in Tempe.

The stressful tasks triggered an increase in systolic blood pressure in oral contraceptive users who smoked, particularly if they smoked immediately before performing the stressful task, the study findings show. Overall, cardiovascular reactivity to stress was higher in oral contraceptive users, but only if they were also smokers.

In all smokers, regardless of whether or not they used oral contraceptives, stress was associated with raised total cholesterol, low-density lipoprotein ("bad") cholesterol, and triglyceride levels in the blood. Davis also observed an increase in fibrinogen, a blood-clotting protein, following stress among all women in the study, according to the report in the March issue of Health Psychology.

The exact mechanisms underlying these interactions between oral contraceptive use, smoking, and stress are unclear.

It is possible that stress causes blood vessel constriction, which, combined with an increase in blood viscosity, or "stickiness," may be the reason that smokers who take oral contraceptives are at increased risk for blood clot formation. This risk may also contribute to an increased risk for heart disease, Davis concluded.

SOURCE: Health Psychology 1999;18.