The two studies in question were presented by experts from Wayne State University at the American Society of Reproductive Medicine's annual meeting in October. Data for the study came from the Women's Health Initiative (WHI). Yet according to the NHLBI, the findings bear no relationship to the findings from the WHI.
Senior WHI statisticians reviewed the two studies after their presentation. They found no evidence that oral contraceptives lower heart disease risk and said the breast cancer results might also have been misleading.
The findings are considered "exploratory" and "should not be used to reassure women about oral contraceptive use," Barbara Alving, MD, WHI director and acting NHLBI director, says in a news release.
The studies conflicted with past research.
"There is a large and reputable body of higher scientific evidence linking current oral contraceptive use to future increases in risk of stroke and heart attack, especially in older women and in smokers," Alving says.
Likewise, previous studies have linked recent use of birth control pills to an increased breast cancer risk. However, some types of oral contraceptives may cut the risk of ovarian cancer and slightly lower endometrial (uterine) cancer risk.
What was the problem with the studies? Design and interpretation flaws, Alving says.
The data came from postmenopausal women who were 50-79 years old when they enrolled in the WHI study. Results relied on the women's memories about their past oral contraceptive use and diseases they had developed. That doesn't always make for solid evidence.
"Because people can forget details, the best studies try to collect these data as close to the event as possible and to confirm any report of disease with hospital records," says Alving.