Charles Andrew Czeisler (born November 1952) is a Hungarian-American physician and sleep and circadian researcher.Czeisler, Charles A. E-mail interview. 24 April 2013. He is a leading researcher and author in the fields of the effects of light on human physiology, circadian rhythms and sleep medicine.
Background and education Czeisler graduated from Harvard College, magna cum laude in 1974, with a degree in biochemistry and molecular biology. His undergraduate thesis was focused on cortisol timing release."Charles Czeisler." Interview. The Science Network. N.p., June 2009. Web. 23 Apr. 2013. <http://thesciencenetwork.org/programs/sleep-2009/charles-czeisler-2> He then studied at Stanford University, where he received his Ph.D. in neuro- and bio-behavioral sciences in 1978 and his M.D. in 1981."Faculty Profile: Charles A. Czeisler, PhD, MD, FRCP." Division of Sleep Medicine: Harvard Medical School. Harvard College, n.d. Web. 10 Apr. 2013. As a graduate student at Stanford, Czeisler continued his research in Dr. William Dement's lab. Dr. Elliot Weitzman, who both worked with and mentored Czeisler, influenced Czeisler to study sleep. Today, Czeisler is the Baldino Professor of Sleep Medicine and Director of the Division of Sleep Medicine at Harvard Medical School. Additionally, he works as the Division Chief of Sleep Medicine at Brigham and Women's Hospital in Boston, Massachusetts."Division of Sleep Medicine." Brigham and Women's Hospital. The Division of Sleep Medicine, 25 Jan. 2013. Web. 11 Apr. 2013.
Czeisler has spent over 40 years researching the relationship between light and human physiology, particularly, the physiology of the human circadian clock. He teaches a course at Harvard College on Circadian Biology for undergraduate and graduate students."MCB 186. Circadian Biology: From Cellular Oscillators to Sleep Regulation." Harvard: FAS Registrar's Office. The President and Fellows of Harvard College, n.d. Web. 11 Apr. 2013. He was ultimately inducted into the Phi Beta Kappa honor society at Harvard College in 1999. In addition to his work at Harvard Medical School and Brigham and Women's Hospital, Czeisler is a Diplomate of the American Board of Sleep Medicine, an elected member of the National Academy of Medicine, the International Academy of Astronautics and the American Clinical and Climatological Association, and a Fellow of the Royal College of Physicians, American Society for Clinical Investigation, and Association of American Physicians.
Family life Czeisler was one of Tibor Czeisler and Wanda Victoria Murzyn's three children. In 1993, Czeisler married Theresa Lynn Shanahan M.D. They now have three children and live in the Boston area. In his free time, Czeisler enjoys swimming, playing pickleball, and slalom waterskiing.
Research interests Czeisler's research focus is the neurobiology of human circadian rhythm, the functions and physiology of sleep, the epidemiology and public health consequences of sleep disorders, and the applications of circadian and sleep principles in clinical medicine and occupational safety and health. He also examines the relationship between the circadian oscillator and sleep homeostasis, including a landmark 1980 Science paper demonstrating that sleep episodes were correlated with the circadian phase of the body temperature rhythm at bedtime and not with the length of prior wakefulness. Czeisler's research interests encompass many areas, including the effects of light on human circadian rhythms, the role of sleep and circadian rhythms in metabolism, the impact of shift work on health and productivity, and the effects of melatonin and melatonin receptor agonists on humans.
Czeisler investigates how the physiological system works to reset the human central circadian pacemaker, located in the hypothalamus and called the suprachiasmatic nucleus (SCN).Joseph S. Takahashi, Hee-Kyung Hong, Caroline H. Ko & Erin L. McDearmon "The genetics of mammalian circadian order and disorder: implications for physiology and disease" Nature Reviews Genetics 9, 764-775 (October 2008) Among his most salient contributions to this research area are a pair of seminal Science original research articles published in 1986 and 1989. The first, entitled "Bright light resets the human circadian pacemaker independent of the timing of the sleep-wake cycle," provided convincing evidence that light influences the human circadian pacemaker, contributing to control of daily variations in physiologic, behavioral, and cognitive function. This finding challenged the then-common idea that synchronization to the 24-hour day accomplished either through social contacts or the sleep-wake schedule. This scientific breakthrough was featured on the front page of The New York Times in June 1989.
Czeisler then led the discovery that light transduced by non-visual input (melanopsin activation) could reset the circadian clock in patients without sight. This indicated that some blind humans can entrain to light through non-visual photoreceptors. Czeisler found that intrinsically photosensitive retinal ganglion cells (ipRGCs) influence both the circadian clock and visual perception, indicating that ipRGCs contribute to "visual" light perception even in the absence of rod and cone photoreceptors. Significantly, this challenged the misconception that rod and cone photoreceptors were the sole receptors for photo-entrainment in humans. In 2002, Czeisler published a study that defended the long-held notion that mammals do not have extra-occular photoreceptors. The findings of his study definitively refuted those of the famous 1998 Science publication, "Extraocular Circadian Phototransduction in Humans," which had reported that bright light behind the knees can help regulated human circadian photoentrainment. Czeisler's study debunked the 1998 publication.
Czeisler has examined the effects of sleep deprivation on the sleep-wake cycle and circadian rhythms, and how this impacts attention performance. He found that bright light duration impacts the circadian pacemaker, melatonin suppression, and sleepiness."Annual Sleep in American Poll Exploring Connections with Communications Technology Use and Sleep". National Sleep Foundation. March 7, 2011. He has also discovered that even room lighting can suppress melatonin production and its duration. Czeisler has also dedicated a portion of his career to examining the effects of light timing, duration, intensity, and wavelength on resetting the pacemaker through ipRGCs, which contain the photopigment melanopsin.
Czeisler's work has many important applications. He showed that sleep deprivation could have adverse consequences affecting obesity and diabetes, among other health problems. He has also investigated the effects of chronic sleep deprivation and restriction, night shifts, and circadian disruption, on neurobehavioral performance and metabolism. Furthermore, Czeisler studied how sleep deprivation impairs the psychomotor performance of night shift workers (2009-2014), specifically surgeons (2009-2013) and residents (2010), police officers (2004-2008),"Sleep disorders linked to poor health and reduced occupational performance in police officers". National Sleep Foundation. Jan 3, 2012 and truck drivers (2012). Other research interests of his include studying wakefulness, sleep deprivation and how it can be prevented, and such influences on the clock as exercise and age. Czeisler's research has been applied to medicine, space travel, and night occupations including shift-work.
As of August 2023, Czeisler has published more than 300 scientific articles, which have accumulated more than 80,000 citations, leading to an h-index of 138.
Summary of selected contributions 1980 – Demonstrated that human sleep duration and organization depend on its circadian phase. 1981 – Characterized and named Delayed Sleep Phase Syndrome (aka Delayed Sleep-Wake Phase Disorder) 1986 – Discovered that light resets the human circadian pacemaker, not social cues or sleep-wake cycles as previously thought. 1989 – Characterized the profound sensitivity of the human circadian clock to light. 1995 – Discovered that blind people can still retain sleep rhythms if their eyes remain intact. 1996 – Characterization of the dose-response relationship between light and circadian phase 1999 – Determined that the average intrinsic circadian period in humans is 24.18 hours, not over 25 hours as previously thought. 2002 – Invalidated reported findings of a study claiming bright light behind the knees impacted human circadian rhythms.Post, Sarah. "Bright Light behind the Knees Is Just Bright Light behind the Knees." Genome News Network. Craig Venter Institute, 16 Aug. 2002. Web. 22 Apr. 2013.Campbell, Scott S., and Patricia S. Murphy. "Extraocular Circadian Phototransduction in Humans." Science. American Association for the Advancement of Science, 16 Jan. 1998. Web. 23 Apr. 2013. 2004 and 2005 – Demonstrated the risks of extended-duration shifts by medical residents, and health and performance benefits of reduced work hours. 2006 – Published on the benefit of modafinil for excessive sleepiness in people with shift work disorder. 2011 – Discovered that women have, on average, shorter intrinsic circadian periods than men 2012 – Demonstrated that prolonged sleep restriction with concurrent circadian disruption impairs glucose regulation and metabolism 2015 – Revealed that evening use of light-emitting devices negatively affects sleep, circadian timing, and next-morning alertness
Advocacy in sleep health and occupational safety In a 1999 interview with the Harvard Gazette regarding his team's characterization of a near-24-hour human circadian period, Czeisler noted that "accepting the near-24-hour period means that all the ideas about daily human rhythms that we take for granted must be rethought.""Human Biological Clock Set Back an Hour." Human Biological Clock Set Back an Hour. N.p., n.d. Web. 24 Apr. 2013. Understanding the internal circadian period makes problems dealing with jet-lag, night shifts, and sleep schedules in orbit more approachable
Guided by the significant real-life implications of his research, Czeisler is a strong advocate for healthy sleep habits. In consulting with the Boston Celtics, Portland Trail Blazers, and Minnesota Timberwolves for the National Basketball Association (NBA) and Cleveland Browns for the National Football League (NFL), he emphasized sleep as the "third pillar of health" alongside nutrition and exercise.Ortiz, Maria B. "To Sleep, Perchance to Win." ESPN. ESPN Internet Ventures, 4 December 2009. Web. 23 April 2013. He instituted structural changes to the teams' schedules to allow for healthier sleep habits, including pushing morning practices into the afternoon and the '2 a.m. rule' which prevents players from traveling if they are going to arrive at their hotel later than 2:00 am.Flannery, Paul. "Person of Interest: Charles Czeisler." Boston Magazine. Metrocorp Inc., May 2011. Web. 22 Apr. 2013.
According to Czeisler, sleep deficiency poses a significant individual and public health hazard as demonstrated by the significant contribution of drowsiness to workplace accidents and motor vehicle accidents. In an interview with the Harvard Business Review, he explains that companies should seek to address this problem by setting behavioral expectations and scheduling policies for employees to avoid accruing sleep deficit.Czeisler, Charles. "Sleep Deficit: The Performance Killer A Conversation with Charles A. Czeisler by Bronwyn Fryer." Harvard Business Review. Bronwyn Fryer. Boston: Harvard Business Review, October 2006.