When we aired Lights Out! in December viewers asked some interesting questions via facebook and twitter. We contacted Dr. Richard Stevens at the University of Connecticut Health Center for answers.
What affect does moonlight have on the sleep cycle? What type of light does it emit? How does this affect people sleeping outside?
Dr. Stevens: Light from the moon is similar in spectrum (color content) as the Sun because it is reflected sunlight. However the intensity is, of course, far lower. A full moon on a clear night will yield less than 1 lux, a measure of light intensity, whereas the Sun on a clear day at noon would measure over 100,000 lux. The Moon's intensity is below a level that has been shown in human subjects to have a measurable effect on melatonin production at night (Brainard et al., 2001).
What happens in northern climates where winter has little sunlight and summer very much? Do people need different amounts of sleep during different seasons? How is the circadian cycle affected?
Dr. Stevens: Melatonin level and duration have an impact on sleep and there is evidence from Finland that, during winter, people tend to have greater melatonin production than during summer (Kauppila et a., 1987). However, this is based on studies of small numbers of people. There is also evidence of a lack of variation in sleep duration over the seasons in the far north of Norway (Johnsen et al., 2012). These apparent discrepancies among scientific studies are a general issue in science of any kind - so we don't really have a concrete answer to that question.
In this case, the results of each study undoubtedly depend in part on whether a person lives in a major city or in the country-side. What is clear is that humans need sleep wherever they live, and that increasing numbers of people in the modern world are not getting enough.
What are the breast cancer rates of Inuit women who live in sunlight six months of the year?
Dr. Stevens: The idea that women of indigenous populations in the far North might have lower breast cancer risk was studied by Erren and Piekarski in 1999. They reasoned that during winter such people would have a maximum of melatonin production during a 24-hour period because of the dark sky most of the time, and the use of only enough light for subsistence during the day. During summer, when the Sun may not set at all, people would still sleep in darkened habitats for six to eight hours. Thus, over the span of a year, total melatonin production would be higher than at lower latitudes. There are a limited number of studies of breast cancer in far north groups (reviewed by Stevens, 2009) and those that have been conducted support Erren and Piekarski's hypothesis.
Of course, indigenous peoples have been fast abandoning their indigenous lifestyles over the last several decades as electricity has invaded even the most remote parts of the world.
Does taking melatonin supplements at night help re-balance the sleep cycle?
Dr. Stevens: There is much interest in the use of supplemental melatonin to aid sleep and to better adjust after trans-meridian air travel. It also holds promise for helping profoundly blind persons to maintain circadian synchrony with the rest of society, and perhaps also helping shift workers better cope with the time of day constraints of their jobs (Blask, 2009).
However, an important caveat is that melatonin is a hormone, and although short term toxicity seems to be nil, we do not know the long term consequences of taking daily pharmacologic doses. In addition, the timing of a supplemental dose during the day is crucial; melatonin taken at the wrong time can disrupt the circadian rhythm instead of support it.