The sun's apparent motion through the sky each day regulates many of the body's hormonal and biochemical processes. In 2002 a new sensory system was discovered in the human eye. This is not involved in vision: it is there to receive and respond to light, sending signals directly to the body's biological clock. This clock, in turn, regulates the secretion of hormones and neurotransmitters in the brain, including melatonin and serotonin. These have a direct influence on our health and the amount of light and darkness we expose ourselves to dictates how much of them is secreted and when.
As well as being our external timekeeper, the sun is our primary source of vitamin D. Solar radiation can trigger skin cancer in susceptible individuals but, paradoxically, the rays that cause tanning and burning are the same ones that synthesise vitamin D in the skin. This has long been known to be essential for strong bones and teeth, but recent research shows that it also plays a pivotal role in maintaining a healthy immune system. There is now a substantial body of evidence that low levels of vitamin D may increase susceptibility to some very common and potentially fatal conditions such as heart disease, stroke, depression, osteoporosis, cancer of the breast, colon, prostate and pancreas, multiple sclerosis, diabetes, and tuberculosis. There is little vitamin D in the normal diet - so anyone who stays indoors when the sun is out may have very low levels of it. And just at the time that scientists are beginning to work out how vital vitamin D is to our health, others are starting to recognise just how common vitamin D deficiency really is. A number of recent studies have found disturbingly low levels of vitamin D across all age groups in Britain, North America, Australia, the Middle East and elsewhere. According to one recent estimate, about one billion people worldwide may have inadequate levels of vitamin D. Even rickets is making an unwelcome return in countries where it was thought to have been eradicated.
Recent discoveries about light and health confirm that light, and especially sunlight, has a profound effect both on our immune systems and our emotional stability. There is a growing body of evidence that the light levels needed to promote wellbeing are much higher than those required for vision, which are the ones typically used in modern indoor environments. There is also evidence that much of the urban population has inadequate vitamin D levels; and that this is due to a lack of sunlight. This presentation discusses contemporary medical research which supports the ancient principle that sunlit environments can be healthier than those that exclude the sun's rays.