Abstract
The primary aim of this thesis was to test the hypothesis that there is a lower prevalence of breast cancer among blind women with no perception of light (NPL) compared to those with light perception (LP). Secondary aims included examination of reproductive outcomes and quantification of the 24 h production of the urinary metabolites oestrone-3-glucuronide (e1g) and 6-sulfatoxymelatonin (aMT6s) among women with LP and NPL. A final aim was to determine the prevalence of circadian rhythm disorders using physiological parameters for classification. A survey (n = 1392) and field study (n = 130, NPL n = 40, LP n = 90) were conducted in blind women. Among survey participants, NPL women reported an earlier age at menarche (age 12.2±1.5 versus 12.5±1.6 years, p < 0.01), which appeared to be related to age at loss of LP (trend p < 0.01). Breast cancer risk was lower among women with NPL compared to women with LP (confounder-adjusted OR = 0.42, 95% CI = 0.21-0.85). The 24 h output of urinary metabolites e1g and aMT6s did not appear to be related to differences in light perception (confounder-adjusted p = 0.42), menopausal status (confounder-adjusted p = 0.86), or circadian type (confounder-adjusted p = 0.34). Among field study subjects with LP 49% were classified as normally entrained, 17% were abnormally entrained, 28% were non-entrained and 6% were unclassifiable. Of those with NPL, 40% were classified as non-entrained 33% were classified as normally entrained 25% were classified as abnormally phased and 3% were unclassified. The results of this of this thesis demonstrate that blind women with NPL have a lower risk of breast cancer, an earlier menarche and are more likely to have an abnormal circadian rhythm compared to those with LP. These differences do not appear to be related to differences in e1g or aMT6s.