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Most life on earth works in close alignment with the sun, and we’re discovering that more-and-more biological processes are governed by the workings of the associated Circadian Rhythm. The quantity, the quality and the timing of our exposure to sunlight is being increasingly understood to have a direct bearing on our sleep patterns. Our exposure to sunlight and our resulting sleep patterns in turn have a great influence on our physical and mental health.

Quantity and Quality

In societies where high intensity modern artificial lighting is not used, from aboriginal communities to Old Order Amish households, exposure to light at night is 3-5 times lower than in electrified homes due to the lower intensity of candlelight. By contrast, during daylight hours the opposite holds true. Such communities often spend far longer outdoors than we do; our artificial light intensity is much weaker than sunlight where waking hours can be 7 times gloomier than those of the Amish.

These relatively new cycles of brighter nights and duller days directly affect our Circadian Rhythm, leading to poorer sleep and upset of our melatonin levels. New research even suggests that sunlight exposure can itself change our risk of developing illness, from depression to diabetes. Clinical studies on shift workers who operate out of phase with their Circadian Rhythm have shown increased risk for metabolic syndrome, type 2 diabetes and cardiovascular disease.

Effects on administration of medicines

Awareness of our circadian rhythms can have surprising effects on the optimal time to take medication. It has been found in cancer treatment, for example, that the tolerance for chemotherapy can be directly impacted by the timing of treatment. Remarkably, side effects such as nausea and loss of appetite can be significantly reduced by timing the doses with people’s Circadian Rhythm. For example, the cancer drug oxaliplatin was initially considered to be very promising, but clinical trials found it too toxic for approval. However, some years later the medicine was revisited to see if it could be administered according to the principles of chronotherapy. Remarkably, not only was it better tolerated than earlier, but some studies even suggested that chronotherapy had even boosted the efficacy of the drug. This led to it being subsequently approved, and it is now considered a blockbuster drug that saves lives. Another interesting example is radiation therapy for cancer – if applied in the morning it results in more hair loss than doing so in the afternoon…because hair grows faster in the morning[i]!

These time-of-day effects are not only confined to cancer treatment. Recently, seasonal flu vaccine was discovered to generate four times as many protective antibodies if given between 9-11am, rather than six hours later[ii].


Our modern life brings enormous benefit, offering society the opportunity to enjoy healthier and longer lives. But benefits often bring unintended consequences. We are now beginning to understand that making modest adjustments to our lifestyle to try to restore our inherent Circadian Rhythm can itself bring improvements to our health.  Even for those who require medication, better outcomes can arise through little more than working with full awareness of our natural cycle – the Circadian Rhythm.