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With the change in seasons now fully upon us, days are getting shorter, and the risk of seasonal affective disorder is turning into very real suffering for literally millions of Americans. Most of this suffering can be prevented, if people recognize the cause of their symptoms and get help.

Seasonal affective disorder (SAD) most often visits patients during the fall or early winter. It has also been called "winter depression" or "winter blues," but its symptoms mimic major depression of any other kind-the distinguishing characteristic in this case being its connection to less sunlight. Those symptoms can include sadness, tearfulness, decreased concentration, decreased self-esteem, low energy, alterations in sleep patterns and appetite, loss of interest in hobbies and work and, in severe cases, thoughts of suicide.

If you have struggled with repeated bouts of depression in the past, it's very important to figure out if you can identify this kind of seasonal pattern. But SAD doesn't necessarily manifest itself with serious symptoms every year, so all of us need to be alert this year to whether we're burdened by it.

SAD costs the economy dearly in lost productivity from employees, employers and entrepreneurs fighting its symptoms. But it will also inflict an additional and very substantial financial burden on the millions of families directly affected, at a time when so many families are struggling already. That's one reason why SAD may be a bigger threat this year than the H1N1 flu, even though SAD gets a lot less attention.

SAD responds to the same treatments used to fight non-seasonal depression. Psychotherapy is tremendously helpful, as is exercise and, when indicated, medication. Another promising and safe treatment is transcranial magnetic stimulation (rTMS), which involves repeatedly stimulating a particular area of the brain using magnetic waves.

I have seen many, many of my patients also benefit tremendously from the use of bright light therapy, which involves sitting for a short time each day in front of specially designed portable lights (which are relatively inexpensive and widely available) that replicate sunlight (without exposing the user to any damaging "tanning" light). One of these devices is called the goLite, but just Googling "bright light therapy for depression" will bring up lots of choices. If fall and winter and "down" times for you, then get one of these lights and use it. It could change your life-for about $150.

It's time we took SAD very seriously, given the fact that it causes so much damage to so many lives and is so responsive to treatment. It's the psychiatric epidemic that comes every year-and one we already know how to defeat.

Dr. Keith Ablow is a psychiatry correspondent for FOX News Channel and a New York Times bestselling author. His book, "Living the Truth: Transform Your Life through the Power of Insight and Honesty" has launched a new self-help movement including