About the WSC Study
When the Wisconsin Sleep Cohort Study began over 30 years ago, very little was known about sleep apnea and little attention was given to sleep problems. Today, the field of sleep medicine has grown tremendously, and the general public is more informed about the importance of sleep. The findings from the studies conducted by the WSC Study have played a large part in helping to improve sleep and health, thanks to the generous contribution of time and effort of our participants “sleeping for science.”
Establishing the Wisconsin Sleep Cohort Study
Between 1989 and 1993, full-time employees of 4 Wisconsin State agencies were sent a short survey about their sleep, general health, and demographics. A subset of respondents were invited to participate in the cohort. The initial research focus of the Wisconsin Sleep Cohort Study was to understand the prevalence of sleep apnea, so individuals with a diagnosis or high risk of sleep apnea were invited to participate, and individuals without a high risk for apnea were selected to match the high-risk individuals in age and sex, in a ratio of 1.5:1.
The Wisconsin Sleep Cohort Study officially began in 1989, and between 1989 and 2003, 1,545 individuals completed their initial overnight sleep study (polysomnography), daytime nap studies (the Multiple Sleep Latency Test), a basic physical exam, and a survey about their sleep, mental health and physical health. Participants were invited to repeat these studies approximately every 4 years.
An Evolving Research Focus
As knowledge has grown about the science of sleep and the importance of sleep health, the research focus of the Wisconsin Sleep Cohort Study has evolved to address emerging scientific questions that are important for public health.
Focus on Sleep-disordered Breathing
The initial research focus of the Wisconsin Sleep Cohort Study was to understand the prevalence of sleep apnea. The publication in the New England Journal of Medicine in 1993 had world-wide recognition, showing that sleep apnea was far more common than previously believed. In 2013, a new publication in the American Journal of Epidemiology showed that the prevalence had increased significantly over 20 years. This information is important for driving progress in diagnosis and treatment of sleep-disordered breathing.
Focus on Cardiovascular and Metabolic Health
As scientific evidence emerged of a link between sleep, cardiovascular health and metabolic function, more detailed measures were added to the surveys and laboratory studies to better understand the relationship. These include measures of blood pressure and body habitus, a blood panel, electrocardiography (EKG), echocardiography, arterial tonometry, retinal tonometry and questionnaires about cardiovascular health history.
Some key findings from this era include that there is a dose-response association between baseline sleep apnea and risk of hypertension after 4 years of follow-up; sleep apnea is associated with subclinical carotid artery disease (plaques and intima-media thickness) after 10+ years of follow-up ; and severe sleep apnea is associated with higher risk for coronary heart disease and heart failure over a decade later.
Focus on Women’s Health
To better understand how sleep changes during menopause, a subset of middle-aged women from the WSC Study completed in-home sleep studies every 6 months across their pre-, peri- and post- menopausal years. This allowed us to capture their menopause transition, shedding new light on how sleep changes during this important life event. Key findings published in 2017 were that sleep-disordered breathing increases across the menopause progression, and that the increase is independent of aging and changes in weight.
Focus on Narcolepsy
Narcolepsy is a chronic neurological sleep disorder characterized by excessive daytime sleepiness and fragmented nighttime sleep. Many patients remain undiagnosed, and available treatments are inadequate. Nap studies are the gold standard test for narcolepsy, and have been included in the Cohort protocols since the beginning of the study. These, in combination with physiological recordings and surveys have contributed to a better understanding of the disease, and ongoing research into better diagnostic tools, including using Artificial Intelligence and Machine Learning to analyze sleep signals (Mignot studies: study 1, study 2, study 3, study 4.)
Focus on Aging
Cohort participants continue to share their time and effort as they get older, and this has created an unrivaled resource for learning how sleep changes as we age. New grants have supported the addition of measures of falls and balance, cognitive performance and the retirement transition.
One group of publications has examined changes in sleep patterns across the transition to retirement. Some key findings on this topic include that when people retire, they tend to nap more and sleep longer and later, and that people who have insomnia are also more likely to retire early due to poor health.
Another theme has been understanding how sleep-disordered breathing impacts health as we age, and factors that might contribute to healthy sleep across the life course. People who are more physically active tend to have better quality sleep and less sleep-disordered breathing as they get older, compared to people who are less physically active. Another key finding was that older people with sleep-disordered breathing report less daytime sleepiness that younger people with sleep-disordered breathing. This is important information for clinical care, where daytime sleepiness is one of the factors considered when determining whether a patient might need to be assessed for sleep-disordered breathing.
Current Study: How does sleep in midlife affect health in later life?
The current wave of testing is focused on understanding how sleep throughout midlife contributes to metabolic, cognitive, and physical function in later life.
The Future of the Wisconsin Sleep Cohort Study
We are extremely grateful to the participants for continuing to give their time and effort. The data collected from WSC Study participants has led to many important papers that have been published in leading medical and public health journals. A full list of publications is available here.
The Wisconsin Sleep Cohort Study welcomes collaborations from researchers. Researchers interested in using Wisconsin Sleep Cohort Study data are encouraged to view a more detailed summary of available measures here. Guidance for accessing data and collaborating with the cohort are available here.
Timeline of Protocols and Data Collection Elements
The WSC Study has been continuously funded by grants from the National Institutes of Health (NIH), including the National Heart, Lung, and Blood, Institute; the National Institute on Aging; and the Center for Health Care Research and Policy. The WSC Study is additionally supported by the University of Wisconsin Institute for Clinical and Translational Research.