BIRMINGHAM, ALA. – Neither depression nor antidepressant use are associated with an increased risk of breast cancer among participants in the Nurses’ Health Study, according to an analysis of data from 67,120 women enrolled in the ongoing prospective cohort study.
Of the women included in the analysis, 2,904 had confirmed breast cancer as of the end of December 2012, including 2,333 with invasive disease. After adjusting for age, body mass index, and menopausal status, no statistically significant associations were seen between invasive or in situ breast cancer and depression or antidepressant use, Katherine W. Reeves, Ph.D. reported at the annual meeting of the American Society of Preventive Oncology.
The point estimates for the odds ratios were all below 1 for in situ disease, indicating a potential protective effect of depression, Dr. Reeves said.
“These were not statistically significant, so I would caution against overinterpreting the results, but it is kind of curious,” she said, noting that the finding may indicate that depressed women are less likely than nondepressed women are to have a mammogram – and thus are less likely to have the opportunity to be diagnosed with in situ disease.
When depression and antidepressant use were included together in the same model, they remained unassociated with breast cancer risk (odds ratio, 0.87), said Dr. Reeves of the University of Massachusetts Amherst.
Study subjects were an average age of 66 years, 8.7% were clinically depressed, and 9.7% used antidepressants. Data on depression and antidepressant use among Nurses’ Health Study participants were collected simultaneously beginning in 2000.
Depression and antidepressant use were self-reported, and depressive symptoms were confirmed using the five-item Mental Health Inventory.
The findings are encouraging; depression and antidepressant use are common and both have been hypothesized to increase breast cancer risk. Some prior studies have found a link between either depression or antidepressant use and breast cancer, and others have not – but most have had important limitations, including retrospective design and inclusion of major depression only, among others, she said.
“To me, though, the most important limitation is that previous studies have not evaluated depression and antidepressant use together,” Dr. Reeves said.
In the current study, which did consider both, no evidence was seen to suggest that depression or antidepressant use affects breast cancer risk.
“It’s typically very unexciting to have to report null results, but in this case, I think this is excellent news and really the best we could have hoped for,” she said, adding that although they are preliminary, the findings should be “very reassuring for the millions of women with depression and/or those using antidepressants.”
“Depression is a very serious medical condition. It deserves to be treated, and it’s nice that these women can take the antidepressants, which so effectively treat this condition without worry that they’re doing something that would adversely affect their breast cancer risk in the future,” she concluded, noting that more sophisticated analyses of the data are planned to consider additional variables, including treatment duration. The analyses will also be repeated in the Nurses’ Health Study II cohort, which is a younger cohort with a higher incidence of premenopausal breast cancer and a greater prevalence of both depression and antidepressant use.