It's that time of year again, the days are shorts, the cloud ceiling lower, our joints and bones creaky in the dampness. While animals go into hibernation for the long, cold months, we humans must learn to cope with change. Like all animals, we follow a circadian rhythm which allows us to prepare for seasonal change. It is said that unless we live by the light, we cannot obtain "optimum health and longevity."

The circadian rhythm affects our brain chemistry, hormones such as testosterone, estrogen and cortisol, heart function, muscular strength and endurance and blood pressure. An area in the brain releases melatonin, which helps to induce our sleep cycle. Melatonin is released at the end of the day when light fades. When the sun rises and melatonin stops being released and we wake up.
      This explains why we have longer sleep cycle through the winter, and shorter in the summer.
      Melatonin is a very important hormone. It is responsible for causing birds to migrate. The winter causes melatonin to rise and testosterone to decrease. So much so that breeding nearly stops in wild animals. The menstrual cycle in females in the far North with very little sunlight also stops for the winter. The increased amounts of melatonin, (and potentially the decreased amounts of estrogen/testosterone)are responsible for SAD or seasonal affective disorder. So if you feel a reduced sex drive and urge to hibernate during the cold Canadian months, you are normal.
      Now there's nothing wrong with supplementing with melatonin if you have sleep problems. It helps to promote restful sleep, and is a good way to battle jet lag, being in front of a computer too long, or disturbed sleep patterns.
     If you are feeling sluggish and unmotivated in the winter be sure to take an omega 3 supplement. There is a direct correlation between omega 3 intake and depression in areas with reduced amount of daylight. Omegas have a role in the production of serotonin and reduce inflammation and the production of inflammatory cytokines. Vitamin D deficiency is also associated with mood disorders and SAD. Supplementing with 800-1000IU daily can improve mood. I find light therapy to be the most effect way to treat seasonal blues. If you have a history of depression or SAD I highly recommend starting therapy in October, to catch symptoms before they really start to take you down.
Life Extension Foundation's information on SAD