Chronobiology and Photoperiodic Effects on Our Health: The Benefits of Summer!

Sunshine and happiness. Summer days are more than just relief from shoveling snow and slipping on ice. There are known health benefits of light due to the brighter longer days. The variation in brightness produces photoperiodic (seasonal) health changes. One of the most important photoperiodic benefits we northerners get is in the extra production of vitamin D during the summer sun days. Did you get the loose it lecture or the blood is clogging lecture from your doc this winter. Well, look forward to improvement there too. Blood cholesterol levels improve in the summer months. And this is not just skipping the French fries for the watermelon (although that will help your cholesterol, well, watch the watermelon, it's about the highest sugar fruit you'll find, so try to find others!). The LDL cholesterol, so often called “bad” cholesterol, is lowest in summer. This was true even for patients on lipid lowering medication, and it has not exactly linked to the increased levels of exercise in summer, although patients do exercise more in the summer than they do in the winter. Along with this surprising finding some researchers, for the trial PROVE-IT found there were less myocardial ischemic events (fewer heart attacks) in summer months as compared with winter months. Interestingly low Vitamin D levels are also associated with hypertension,vascular diseases and heart failure. Individuals suffer less from depression in the summer. Seasonal Affective Disorder (SAD) is a condition of depression or sadness that occurs during the dark winter months,and exposure to the brighter days, especially bright light in the morning seems to be both preventive as well as curative. No one has ever discovered why, but it seems to have a specific effect on brain chemicals that causes this. However, SAD has rarely been reported in individuals over the age of 55! Why this should be we do not know. We do know that the pineal gland rhythms do begin to significantly blunt as we age, in fact the gland calcifies and begins to show up on an x-ray. Knowing that SAD is more rare in the longer light filled days physicians have begun to employ light to treat a variety of conditions: Bright light is now used to treat SAD and the bright light therapy has been used for a number of other psychological conditions including non-seasonal depression, bipolar depression, chronic depressive disorder, ante- and postpartum depression, late luteal phase dysphoric disorder, circadian phase sleep disorders, jet lag, shift work problems, behavioral disturbance, insomnia and inorganic dementia. Much work remains to be done, and scientists have to correlate the light therapy with the levels of the corresponding hormones and brain transmitters that are responsible for the eitiologies of the various condition. Chronobiology, the study of our daily biological clocks, has been thought more worthy of dinner conversation than a serious discussion at your check up. Mystics thought that we had a secret vestigial third eye known as the pineal gland. It got this reputation because of the photoresponsive cells of the gland in lower vertebrates. The philosopher RenĂ© Descartes believed the pineal gland was the seat of the soul. And cyclic behaviors became the rage to study. In my field, it’s the “woman’s cycle” but we have known rhythms in how often we get contractions when pregnant and sex drive cycles too! But menstrual cycles not with standing, scientists are discovering many physiological functions are controlled by 24 hour rhythms. Our lung functions best at 4 in the afternoon and poorest at 4 AM, as a result the worst asthma episodes are from 10 pm at 7 AM and this almost exactly parallels the lowest levels of ;cortisol which occurs at midnight, a hormone that can combat inflammation, which then peaks around 8 AM. This phenomenon has been called nocturnal asthma and about 75% of serious asthmatic attacks are during these night hours. Actually many hormones and brain chemical transmitters have to work in together to achieve this sequence of events that bring about the orderly circadian rhythms that make up human physiology. The pineal gland primarily secretes melatonin thought to be the primary regulator of our biological clock. Newly reported in March 20, 2009 issue of The Journal of Biological Chemistry by a group of researchers at the National Institute of Health was that the activity of over 600 genes of the pineal gland act in synchrony over a 24 hour period of time. And the retina has active function of many of these genes, which can help explain the link with the length of daylight and the summer season. There is much to learn, the pineal gland is controlled by the suprachiasmic nucleus at the base of the brain. The suprachiasmatic nucleus has a role in coordinating the signals from the retina to the pineal gland and has become to be called The Mind’s Clock. So we are gradually coming to understand that time of day is critical in the function of our physical selves. Now before you get so excited about sunshine and bathing your retina, remember, these things are seasonal too: summer diarrhea in children, herpangina infections in young adults, lyme disease, mold allergies, and several dozen other common illnesses including more colds. One of the newest studies has shown it's more likely that you will have become anorexic if you were bone in spring or summer (least likely in the fall), a very odd, second generation effect of light apparently, if we are to believe this new research . So why not get your jar out and get that sunscreen on, and don’t forget to slather some disinfectant on your hands! HAPPY SUMMER!


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