The Doctor Is In is an occasional series where JHU Press authors discuss the latest developments and news in health and medicine. guest post by Mark D. Miller, M.D. With the holiday season kicking off at Halloween these days (at least you'd think so from retail store decorations), many people begin to feel a sense of dread instead of high holiday spirits. Several factors can be responsible for this phenomenon: some people are shut-ins; others miss loved ones who have died or live too far away to visit; and still others feel empty because of commercialism or Seasonal Affective Disorder (SAD). SAD—which is sometimes called winter blues or cabin fever—is characterized largely by an energy crisis in the sufferer, who feels listless, avoids socializing, and experiences a decline in libido. SAD sufferers trend toward couch potato status. They shun activity, instead lounging around or staying in bed for long periods, then rise in the morning feeling unrefreshed. They often experience weight gain as a result of munching carbohydrates. To try to feel better, some take to drinking more alcohol, which compounds the problem further. What causes SAD? It turns out that humans are affected by the sun, much like bears that hibernate or birds that migrate. All three species collect light through their eyes and relay it to brain circuits that act like internal clocks. These “clocks” are, in turn, reset by prevailing sunlight. Sensing the shortening length of the day triggers the species-specific behaviors associated with the winter season. In a milder version of hibernation, most people will slow down their activity schedules, sleep longer, eat more, and gain a few pounds in the winter months, with a reversal in the spring. Just as hibernation helps bears to survive the winter, humans probably evolved to survive winters better by conserving energy. About 10% of the population experience a more severe version of this seasonal energy conservation, however, which disrupts their work ability and often their marital relationships. These individuals are poorly sensitive to day/night changes such that their biological clocks are not properly reset by the sun. As a result, their brains are not in synch with the 9-5 workday most of us operate within. This “out-of-synch” brain can produce the symptoms of SAD. How can SAD be helped? In short: get more light in your life! Increased light exposure is an especially effective remedy if you are of Mediterranean ancestry: living near the equator meant that it was not necessary for Mediterranean peoples to evolve a sensitive light/dark sensing capability (because it is always sunny!). Opening your drapes during the day, taking a walk outside in the morning, avoiding the night shift, traveling closer to the equator, taking up skiing, moving out of that basement apartment, and getting your cataracts removed all can improve or eliminate SAD symptoms. Special light delivery devices, which glow as brightly as a 7 a.m. sun (10,000 lux), can also help; so can sitting in front of a so-called “sun box” for 20-60 minutes every morning while you drink your tea or coffee. To learn more about treating the symptoms of SAD, check out the book Winter Blues, by Norman Rosenthal. A nice collection of light delivery devices can also be found on Amazon. Before you light up artificially, however, ask your physician to check your thyroid hormone and vitamin B12 and D levels. You can become fatigued or depressed if these blood levels are too low. Some people with SAD will require antidepressant medications in addition to more light, and those who already suffer from depression might benefit from adding light in the wintertime for those seasonal dips in mood. Don't just wait for spring to arrive: ask your doctor to help decide if you suffer from Seasonal Affective Disorder. Mark D. Miller, M.D., is associate professor of psychiatry at Western Psychiatric Institute and Clinic, University of Pittsburgh Medical Center. He is coauthor of Depression and Anxiety in Later Life: What Everyone Needs to Know and Living Longer Depression Free: A Family Guide to Recognizing, Treating, and Preventing Depression in Later Life, also published by Johns Hopkins. The information provided in this blog post is not meant to substitute for medical advice or care provided by a physician, and testing and treatment should not be based solely on its contents. Instead, treatment must be developed in a dialogue between the individual and his or her physician. This post has been written to help with that dialogue. The services of a competent medical professional should be obtained whenever medical advice is needed.