Women who are totally blind before the age of 65 have a significantly lower risk of developing breast cancer, according to the results of a study published in the
British Journal of Cancer.
Breast cancer is the second leading cause of cancer death in women in the United States, with approximately 200,000 cases diagnosed each year. Although several risk factors have been associated with breast cancer, the cause of the majority of cases of breast cancer remains unknown. Researchers continue to explore the causes and risk factors for this disease in an effort to improve methods for screening and prevention.
In the past, researchers have theorized that melatonin offers a protective effect against breast cancer. Previous experimental studies have indicated that increased nocturnal exposure to visible light reduces melatonin levels and leads to an increased growth of breast cancer. Although exposure to light suppresses the secretion of melatonin, this suppression occurs to a lesser degree in totally blind people.
In order to further investigate the melatonin hypothesis, Norwegian researchers conducted a cohort study of Norwegian visually impaired women. The researchers used data from the Norwegian Registry of Blindness to identify a cohort of 15,412 visually impaired women, of whom 396 were totally blind. The researchers then followed these women to investigate the incidence of breast cancer and evaluate the relationship between visual impairment and breast cancer risk.
The results indicated that blind women had a 35% reduced risk of developing breast cancer. Moreover, women who became totally blind prior to age 65 had a 50% reduced risk. The results did not indicate any association between visual impairment short of total blindness and breast cancer.
Since blind women are not ocularly receptive to light and may maintain melatonin production regardless of light exposure, the researchers concluded that this melatonin production may offer protection against breast cancer. Thus, the researchers concluded that their results support the melatonin hypothesis. (
British Journal of Cancer, Vol. 84, No. 3, pp. 397-399, 2001)