It’s estimated that most people spend one-third of their lives sleeping, but until recently, the links between sleep and health were not well understood. Recent research has identified relationships between disrupted sleep and increased risk of obesity, diabetes, cardiovascular disease, and some cancers, suggesting that sleep has significant effects on health and well-being.
There are an estimated 4.1 million shift-workers in Canada, and approximately 1.9 million regularly work shifts between midnight and 5AM; these workers are the largest group at risk of disrupted sleep. According to a Statistics Canada Survey of nurses from 2005, six percent of B.C. nurses work permanent night shifts, and an additional 45 percent work mixed shifts, including nights. This suggests that slightly more than half of all 38,000 registered nurses in B.C. suffer from regular circadian disruption due to shiftwork. In fact, in 2010, IARC classified shiftwork with circadian disruption as Group 2A, “probably carcinogenic to humans.” In particular, IARC identified increased breast cancer risk in night shift-workers.
The ICOS study (Improving Cancer-related Outcomes in Shiftworkers) is funded by the Canadian Cancer Society and led by Dr. Carolyn Gotay, Canadian Cancer Society Chair in Cancer Primary Prevention at the University of British Columbia. The study tested whether a sleep hygiene intervention for women who work shifts could reduce their risk of breast cancer.
Study participants were 47 women (including 23 nurses) from the Vancouver region. On average, these women had worked seven night shifts per month for more than 16 years. At baseline, about four in five (79 percent) reported poor sleep. Since obesity is an additional risk factor for breast cancer that is linked to poor sleep, participants also self-reported their BMI and were categorized as normal weight, overweight, or obese.
The sleep intervention consisted of 10, telephone-delivered cognitive behavior therapy (CBT) sessions. CBT is a psychotherapeutic method that focuses on changing unhealthy patterns of behaviour and thinking, and it has been endorsed as a first-line treatment for insomnia by a National Institutes of Health Consensus Conference and the British Medical Association. The intervention was delivered by an experienced sleep counselor.
Six months after the intervention, the proportion of participants reporting poor sleep had decreased by more than one-third, from 79 percent to 49 percent. This positive impact was maintained when we went back to the women six months later, a year after they began the study. The effect was stronger in women with BMIs less than 25, but it was also statistically and clinically significant in women who were overweight and obese. This promising finding suggests that a sleep hygiene program like the one used in the ICOS study can result in significant and lasting improvements in sleep quality in night shift-workers.
We are still analyzing other data collected in the study, including information about health behaviours, objective measures of physical activity, and biological indicators in blood and saliva. We are very grateful to the nurses who took part in this research – we couldn’t have done it without them! We’ve already learned a lot from this study, and we plan to build on our findings in future research. In particular, we are thinking about providing sleep hygiene sessions for nurses who are just beginning their careers as night shift-workers.
If you have comments about this idea, suggestions for other sleep research that would be helpful to you, or if you’d like more information about the ICOS study, please contact Jennifer Parisi, Communications Director at the Centre of Excellence in Cancer Prevention (communications@cancerprevent.ca).
About Dr. Carolyn Gotay, PhD
Carolyn Gotay, PhD, FCAHS is Professor and Canadian Cancer Society (CCS) Chair in Cancer Primary Prevention at the University of British Columbia (UBC). She also holds an appointment at the BC Cancer Agency. Dr. Gotay received her PhD in psychology from the University of Maryland, and she came to UBC in 2008 after positions at Gettysburg College, the University of Calgary, the (US) National Cancer Institute, and the University of Hawaii.