Till Roenneberg

Aside from human chronobiology, Roenneberg has significantly contributed to other aspects of the chronobiology field. He has done extensive work on dinoflagellates, a unicellular organism, and has been able to show that even this simple organism is capable of possessing two independent rhythms, providing evidence that a single cell can have two different oscillators. In addition, his work on dinoflagellates has been able to show that these two independent oscillators differ to a significant extent in that they respond differently when treated with various light pulses. They found that the two oscillators have varying sensitivities to different types of light. The B-oscillator is most sensitive to blue light while the A oscillator is sensitive to both blue and red light.[4][5][6]

Roenneberg has also completed work on Neurospora crassa, determining the masking qualities of entrainment through a Frequency (gene)-null circadian oscillator. He observed in the period of spore production (conidia bands) the phenomenon of masking, an unexpected effect on circadian entrainment due to a particular zeitgeber (such as light[7] or temperature). Masking has significant implications not only for future studies – which must attempt to demask affected data – but also in relation to entrainment in everyday life.[8]

One of Till Roenneberg's most renowned accomplishments is the development of the Munich Chronotype Questionnaire (MCTQ). As a collaboration with Martha Merrow at LMU Munchen, the MCTQ samples sleep and circadian rhythm data from more than 25,000 participants. Unlike other chronotyping methods, which address the psychology of sleep, the MCTQ measures the phase angle of entrainment,[9] the difference between an organism's intrinsic circadian period and the environmental light cycle. Thus, this questionnaire is the first to use a biological foundation, rather than psychology to determine the basis of sleep schedules.[10]

Questions about work day and free day sleep schedules, work details, and lifestyle provide data to aid in the understanding of the interplay of biological clocks and social influences. Such research has led Roenneberg to his theory of social jet lag. The MCTQ categorizes each participant into one of seven chronotype groups and utilizes data on participants’ midsleep phase and sleep debt to survey what “type” of sleeper each person is, such as late sleepers, slightly late sleepers, early sleepers, and others. From these data, the MCTQ offers methods to make up for sleep debt (if any), and offers suggestions on what to do to wake up earlier or sleep later.

This chronotype questionnaire is important because it delves into the social aspects of circadian rhythms. By testing behavior rather than directly testing genetic factors, the MCTQ may offer new information regarding how the effects of external factors, including geographic location, seasons, obesity, social jet lag, or shift work,[11] may relate to genetic predispositions of circadian rhythms.[12]

Roenneberg released a book in March 2012 titled Internal Time: Chronotypes, Social Jet Lag, and Why You're So Tired where he explains the concepts behind circadian rhythm to the masses. One of the major points in his book is, "Early birds and night owls are born, not made."[1] Roenneberg wanted to rid people of labels such as "lazy" that frequently get placed upon those who wake up late. With this book, he wanted to deliver his point that these sleep patterns are due to people's genetics and are not from choice. He discusses how everyone is born with an internal clock, and living a lifestyle in dissonance with this inherent biological clock puts individuals at greater risk for health problems. Roenneberg introduces the term “social jet lag," saying it is more dangerous than normal jet lag because social jet lag forces individuals to persistently go against their biological clock in a consistent light/dark cycle. In this book, he defines social jet lag as “the difference between midsleep on free days and midsleep on work days." Free days are defined as days without an alarm clock, where one naturally wakes up, and work days where one wakes up with an alarm clock. Midsleep is defined as the midpoint of an individual's sleeping period.[13] One of the significant health risks of social jet lag is obesity,[14] and Roenneberg claims that for every hour of social jet lag, the probability of being overweight increases by approximately 33%.[15] In fact, social jet lag is so prevalent that Roenneberg claims that 87% of the population of Central Europe suffers from social jet lag to some degree.[1][16]

Roenneberg also claims that adolescents, biologically, have an internal clock that causes their midsleep to fall later than young infants and adults. Thus, teenagers are not lazy, but are simply following their internal rhythms by going to sleep later and waking up later. This late midsleep pattern changes after adolescence, but at different points for men and women. Women's midsleep changes around age eighteen, while men's midsleep changes at the age of twenty-one. Forcing teenagers to wake up early, against their internal rhythms, leads to stress. As many studies have shown, stress leads to unhealthy decisions such as smoking and drinking.[17]