A new study has reported that women who regularly use pain killers have lower circulating levels of estrogen, which could reduce their risk of breast or ovarian cancer. The study was designed to investigate the relationship between use of aspirin, nonaspirin nonsteroidal anti-inflammatory drugs (NSAIDs), and acetaminophen and circulating sex steroid hormone levels. Prior population studies have reported that regular use of analgesics may decrease the risks of breast and ovarian cancer. The study included 740 postmenopausal women in the Nurses' Health Study. Participants self reported their analgesic use in either 1988 or 1990 and provided a blood sample during the period 1989 to 1990.

Significant inverse trends were observed between the estimated number of aspirin tablets per month and concentrations of estrone and estrone sulfate. Participants who used NSAIDs (aspirin and nonaspirin) at least 15 days per month had significantly lower levels of estradiol compared with women with no NSAID use. Frequency of use of all analgesics (aspirin, other NSAIDs, and acetaminophen) was found to be inversely associated with concentrations of estradiol, free estradiol, estrone sulfate, and the ratio of estradiol to testosterone. The authors conclude that postmenopausal women who regularly use aspirin and other analgesics may have lower estrogen levels than nonusers, which could contribute to a decreased risk of breast or ovarian cancer among them.