Grant: Doctoral Award - Frederick Banting and Charles Best Canada Graduate Scholarships

Studies of both women and men working night shifts have demonstrated links between shift work and some cancer sites, such as breast, endometrium, colon and prostate. Many scientists think that these relationships are determined partly by increased exposure to light during night shifts, which can decrease levels of melatonin, a hormone produced in a pattern that follows daily rhythms, which can increase cancer risk. These daily (circadian) rhythms are coordinated by a set of eight "clock" genes. Some variants of these clock genes may be linked with cancer risk, although the mechanism through which this occurs is not known. Further, it is unclear whether the observed effect of these genetic variants on cancer risk occurs independently or whether the effects of clock genes and light at night exposure on cancer risk may be related. This research will examine the relationships of both light at night exposure and clock gene variants with melatonin levels and breast cancer risk. Links with melatonin will be investigated through a longitudinal study of female rotating shift nurses, where light exposure is assessed using a light data logger and melatonin levels are obtained from blood, urine and saliva samples. Blood samples will also be used to characterize clock gene variants. The relationship between clock genes and breast cancer risk will be examined through another study that involves individuals with and without breast cancer, where again blood samples will be used to determine the presence of clock gene variants. This project will contribute to the understanding of the biologic mechanisms underlying the relationship between shift work and cancer. Since shift work is a necessary component to many occupations, a greater understanding of these mechanisms will aid in the development of shift work patterns that are best for health.