Background: Shift work is associated with increased risk of cardiovascular disease and cancer, where decreased melatonin has been proposed as an intermediate in the causal pathway. The influence of physical activity on melatonin has rarely been studied in an observational setting, and it may be important in mediating the effects of shift work. We aimed to assess the influence of energy expended during physical activity of different intensities on melatonin among rotating shift nurses. We hypothesized that physical activity before the night shift would lessen the decrease in melatonin production that occurs with exposure to light at night. Methods: 123 female rotating shift nurses working at Kingston General Hospital were recruited over a one-year period. Physical activity and sedentary behaviours for each participant were recorded during both a day and a night shift using activity diaries, and analysis was restricted to activities between 3 p.m. and 7 a.m. Concentrations of urinary 6-sulfatoxymelatonin, a melatonin metabolite, in morning void urine samples were analyzed for each shift. Results: The average age of participants was 41 years, and 60% were overweight or obese (body mass index ≥ 25 kg/m2). An average of 6.9 and 5.2 hours of sleep were reported after the day shift and night shift, respectively. Sedentary behaviours such as standing and television watching accounted for over half of the total reported energy expenditure. During the day shift, energy expended in moderate and vigorous intensity physical activity between 3 p.m. and 7 a.m. was negatively associated with melatonin levels (p=0.024, R2 = 0.09). During the night shift, energy expended in sedentary behaviours was negatively associated with melatonin levels (p=0.008, R2 = 0.03). Conclusions: Physical activity energy expenditure explains only a small amount of melatonin variation, suggesting that other factors are influencing melatonin production, or that melatonin production is minimally effected by these patterns of physical activity. / Thesis (Master, Community Health & Epidemiology) -- Queen's University, 2010-09-01 11:22:35.915

Background: In 2007, the International Agency for Research on Cancer classified shift-work involving circadian disruption as a “probable carcinogen.” One proposed pathway for this relationship involves nighttime light exposure and subsequent decreases in melatonin production. It is postulated that melatonin, a cancer-protective hormone, may influence patterns of sex hormone production that in turn influence breast cancer risk. The purpose of this study was to investigate the relationships between night shift-work history, melatonin and sex hormone levels among shift-working women. Methods: 82 pre-menopausal nurses who work a rotating shift pattern of two days (7AM-7PM), two nights (7PM-7AM), followed by five days off participated in two study periods approximately six months apart (in summer and winter), each taking place during a day shift of the normal rotating shift pattern. Creatinine-adjusted melatonin metabolite concentrations were measured from morning void urine samples, and estradiol, estrone, progesterone and prolactin concentrations were measured from fasting blood samples taken at the same time. Other pertinent information was collected by measurement (weight, height) and by self-report via questionnaire. We examined melatonin-sex hormone relationships within each of two seasons, and across seasons, to investigate two hypothesized latency periods for influences of melatonin levels on sex hormones. Multivariate linear regression was used to explore relationships, with adjustment for confounders including age and body mass index. Results: An inverse relationship between melatonin and estradiol was suggested in winter (β = -0.13, p = 0.11), and a positive relationship was suggested for increasing estrone with increasing melatonin tertile in summer (p = 0.07), after multivariate adjustments. Melatonin was not associated with other hormones in either season. On investigation of a longer latency period, melatonin in the first season was not associated with sex hormones in the second season. While those working night shifts for 20 years or more had higher mean levels of estradiol, estrone and progesterone, results were not statistically different from those with a shorter history of night work. Conclusions: The results of this study do not provide evidence to support the proposed biological pathway involving altered melatonin and sex hormone levels as intermediates between shift-work and breast cancer risk. / Thesis (Master, Community Health & Epidemiology) -- Queen's University, 2010-09-14 11:42:06.201

Thesis (Ph.D.) -- University of Adelaide, Dept. of Obstetrics and Gynaecology, 1998? / Bibliography: leaves 162-197.

Thesis (PhD) - Swinburne University of Technology, Brain Sciences Institute, 2007. / Doctorate of Philosophy, Brain Sciences Institute, Swinburne University of Technology - 2007. Typescript. "April 2007".

Thesis (Ph.D.)--University of Calgary, 2000. / Includes bibliographical references.

Includes bibliographical references (p. 117-140).

Thesis (Ph. D.)--University of Hong Kong, 1994. / Includes bibliographical references (leaves 72-104).

Thesis (Ph. D.)--University of Hong Kong, 1994. / Includes bibliographical references (leaves 79-105).

Thesis (M. Phil.)--University of Hong Kong, 1999. / Includes bibliographical references (leaves 46-61).

Thesis (M.S. in Operations Research)--Naval Postgraduate School, September 2002. / Thesis advisor(s): Nita L. Miller, Samuel E. Buttrey, Susan M. Sanchez. Includes bibliographical references (p. 147-149). Also available online.