Maybe it's just me, but when winter drags on and so many days are too cold, too windy or too icy to get out in the sun, my sense of well-being heads south. It gets difficult to crawl out from under the covers. I crave carbs more, can't seem to get alert in the mornings and struggle with brain fog, lethargy and a lack of real passion for anything.

As it turns out, I'm not the only one. The National Institute of Health estimates more than 36 million Americans suffer depressive symptoms brought on by winter. What's going on here? Why is this time of year, with its shorter days and less sunlight, so tough for so many of us? What is it our bodies need from sunlight?

Is it just vitamin D? That's what I assumed when I lived in gloomy Portland, Ore., where the dark clouds hang overhead for nine months at a stretch. It must be a lack of vitamin D, which leaves the whole city in a state of depression by January. After five years there I thought I had "acclimated." I actually had just gotten accustomed to living with a low level of depression. Then I moved to sunny Colorado and it felt like someone had flipped on a light switch in my soul!

Then, over the years I got used to the abundant sunshine. Now a mere week of gloom can send me into a noticeable funk.

It's called Seasonal Affective Disorder, or SAD, which can range from fairly mild to a serious clinical depression. It isn't just limited to places like Portland and Alaska; even here in sunny Colorado Springs it can be difficult to get enough natural sunlight this time of year, especially if you work in a windowless cube, drive to work in the dark, and your west-side home is already swallowed up in the shadows of the mountains by the time you return there.

As I researched light therapy, the No. 1 AMA recommended treatment for SAD, I found the science behind it fascinating. It isn't really about a vitamin D deficiency. It seems there is a part of the brain, the Suprachiasmatic Nucleus or SCN, which acts as a master body clock regulating the body's circadian rhythms, including the sleep/wake cycle and the mood/energy cycle. The SCN controls the timing and volume of the body's production and dispensing of hormones and neurotransmitters.

Timing is very important. Morning sunlight is the natural signal taken in by melanopsin photoreceptors in the retina and carried along the optical nerve to the SCN, telling it "OK, brain, it's time to wake up and start making serotonin." Serotonin makes the body feel positive, alert, energetic and ready to take on the day.

These light signals also suppress the production of melatonin during the day. At night, the natural signal of darkness tells the brain it's time to produce melatonin, extracting it from serotonin. Melatonin causes the body to withdraw, pull back, mellow out and prepare for sleep. Melatonin produced during the day, makes it hard to focus and makes a person lethargic, sleepy, irritable and blue, if not downright depressed.

The good news is light therapy can be an effective substitute for morning sunlight when the real thing is hard to come by. Special light boxes can be used to reset the body clock, stimulate production of serotonin, and suppress the production of melatonin.

Early light therapy researchers recommended using a full-spectrum lamp with a strength of 10,000 lux to be effective. But more recent studies at Thomas Jefferson Medical University have narrowed in on the specific spectrum of blue light wavelengths to which the SCN responds the most dramatically. By focusing on this spectrum, the 446 - 477 nanometer range, which is five times more effective than other wavelengths, cutting edge light therapy devices are able to give you better results in less treatment time with more convenient, less harsh, UV-free portable light boxes. 10,000 lux is no longer necessary.

Recent light therapy research has also confirmed these lights can be helpful in the treatment of other types of depression, sleep disorders and a host of other ailments. The antidepressant impact of light therapy is very real and generally can be felt within just a few days. It has dramatically helped me!

Depression, seasonal or otherwise, can rob you of productivity, joy and pleasure, reducing your existence to a struggle to get through the day. Fortunately, you don't have to grit your teeth and suffer through it. There are options. Light therapy might just be worth a try.

For more information, go to: www.bestlighttherapy.com