Boston, Massachusetts (PressExposure) October 22, 2009 -- Researchers at Brigham and Women's Hospital (BWH) have found that totally blind women have more than a 50 percent reduction in breast cancer compared to visually impaired women and that this same group of totally blind women have an earlier menarche, or first menstrual period, when compared to blind girls with some light perception. These findings are published online in two separate papers appearing in Cancer Causes and Control and Ophthalmic Epidemiology.
The role of light on human reproductive development is unclear and much of the research has been focused on the differences between blind women with varying levels of vision compared to women with no visual impairment. Researchers in these studies evaluated the differences in nearly 1,400 blind women who either had no light perception or were blind but retained some light perception.
In the first study, researchers report that of the 66 cases of breast cancer, there was a significant difference in the number of cases in each group even when controlling for known reproductive risk factors for breast cancer, with 11 cases of breast cacner in blind women with no light perception compared to 55 cases in blind women who retained some light perception.
In their second study, researchers looked at the age of the first menstrual period in these blind women and found that blind women with no light perception have their first period at an earlier age when compared to blind women with light perception. Researchers also found that the earlier the loss of light perception in blind girls, the earlier the age of the first period.
"These reproductive differences are opposite of what you would expect for a group with decreased cancer rates," said Erin Evans, the lead author on both papers and a doctoral candidate in the Division of Sleep Medicine at BWH. "An earlier menarche is associated with an increased risk of breast cancer in sighted women, so taken together; these two recent findings suggest that it is not reproductive differences that account for the lower risk of breast cancer among blind women. More research is needed to examine how production of the hormone, melatonin, and the internal circadian coordination may be responsible for this observed lower risk of breast cancer," she added.
"Although these findings are not entirely new discoveries, they are more detailed than previous research and provide additional insight into the role that light plays in cancer risk as it relates not only to blind women with no light perception, but also to shift workers and to those who sleep for short durations throughout the night," said Steven Lockley, PhD, senior author of the papers and a researcher in the Division of Sleep Medicine at BWH.