Philip J. Goscienski, M.D.
September 2006
Try as we might, it's hard to imagine life without artificial light. On any given evening in a typical modern home, scores of electric lights permit unrestricted work and play activity. Yet this age of illumination represents only a tiny fraction of the time during which Homo sapiens evolved in nothing but natural light. Our bodies still function on this ancient day/night pattern, the circadian rhythm. This rhythm influences hormone levels and numerous chemical processes. When early Stone Age people started using oil-burning lamps they set in motion a disturbance of this pattern and Thomas Edison's incandescent bulb magnified that disruption a thousand-fold. Only a few generations have passed since we have artificially lengthened our daytime, not long enough in evolutionary terms for our innate body rhythm to adjust.
Jet lag is a stark reminder of our body's natural day-night rhythm. Even frequent travelers never adjust to it completely. Skipping across several times zones within just a few hours puts us out of synch with the brain's production of melatonin, a hormone that influences sleep and wakefulness. Over the long term, when we suppress melatonin by increasing our exposure to light during the 24-hour cycle it may increase the risk of certain cancers.
Physicians have known for decades that shift workers are more prone to various illnesses and accidents than persons who work a regular daytime schedule. The body's release of cortisol (known as the stress hormone), growth hormone and testosterone is related to patterns of daylight. This hormone-release sequence became finely tuned over more than two million years and it should be no surprise that a gross disturbance of the pattern could cause major health problems.
Several factors influence our hearth rhythm. A healthy nervous system helps to regulate the way the heart responds to the normal stresses and variability of daytime routines. Shift work disturbs the balance of this nervous control. Over the long term it may contribute to a higher incidence of heart disease that has long been known to affect shift workers.
Employees on late shifts become less alert and their work becomes less efficient. They also average about one hour less sleep than day workers. All these factors contribute to fatigue and accidents.
Exposure to light increases levels of estrogen hormone, perhaps explaining why women who work night shifts have a greater incidence of breast cancer. Longer exposure to estrogen on an almost daily basis for several years could trigger changes in cells within the breast that lead to cancer.
Could exposure to longer periods of light affect male fertility? Sperm counts appear to be declining among Western populations whose day/night patterns have changed a great deal in the past century. One explanation could be that light-induced increases in estrogen levels that are barely measurable could affect sperm production.
Cancer cells grow faster during some parts of the day. One of the newer approaches to treatment is the proper timing of chemotherapy based on this observation.
Scientific interest in biorhythms is nothing new but recent advances in genetics and biochemistry are helping us to understand how the day/night cycle influences disease patterns and they might even determine what time of day is best to take antibiotics, heart and blood pressure medications, pain relievers and hormones.
Philip J. Goscienski, M.D. is the author of Health Secrets of the Stone Age, Better Life Publishers 2005. Contact him at drphil@stoneagedoc.com.