By Richard Harkness
Enquirer contributor

Question: My daughter takes birth control pills and I'm concerned because, like hormone replacement therapy, they contain estrogen and progestin. Since hormone replacement therapy was found to increase the risk of breast cancer, wouldn't the pill do the same?

Answer: Many women are rightfully wondering about this. Raising concerns even more is the observation that estrogen doses in birth control pills are substantially higher than those used in hormone replacement therapy (HRT).

Even so, the news is much better for oral contraceptives: According to the latest study, birth control pills don't appear to boost the risk of breast cancer.

How to account for this seeming paradox? One possible explanation is that oral contraceptives use a different form of estrogen than the HRT used in the research studies. Another, and perhaps more likely, explanation is age. Cancer risk increases with age, and women who use the pill are younger than those who use HRT.

Past epidemiologic research has yielded conflicting results on a possible link between oral contraceptives and breast cancer. A 1986 study of more than 8,000 women found no increased risk of breast cancer. In contrast, a 1996 review of numerous studies indicated a slightly increased risk, which was thought to go away 10 or more years after stopping oral contraceptives.

The latest study was published in a recent issue of the New England Journal of Medicine. It evaluated more than 9,000 women ages 35 to 64 years, an age group thought to be at higher risk of breast cancer. As it turned out, researchers found no increased risk of breast cancer among women who were currently taking oral contraceptives or who had taken them in the past, including those with a family history of breast cancer.

The one caution light in this study: There seemed to be a small increased risk of breast cancer in older women (ages 45-64 years) currently on oral contraceptives compared with women in the same age range who had used oral contraceptives in the past. However, because the number of women in this age group was very small, more research is needed.

As with HRT, oral contraceptives have been associated with increased cardiovascular risk. These problems were more common with older oral contraceptives, which contained higher amounts of estrogen than today's oral contraceptives. Smoking really ratchets up the risk, particularly in women over age 35 on oral contraceptives who smoke more than 15 cigarettes a day.

The good news is that healthy, nonsmoking women who take low-dose oral contraceptives appear to have no increased risk for heart attack or stroke, and much less risk of blood clots.

E-mail rharkn@aol.com.