Winter does not officially begin until Dec. 21, but as the days grow shorter and sunlight exposure becomes scarcer, seasonal affective disorder (SAD) becomes more common. SAD is a type of depression that occurs during the late fall and early winter and often ends by spring or early summer. The exact cause of SAD is unknown, but research points to lack of light as the main contributor.

Do you have SAD?

For people to be formally diagnosed with SAD, they must meet the criteria for major depressive episodes coinciding with the fall and winter months for at least two years. Common symptoms of a major depressive episode include

• feeling hopeless or worthless
• losing interest in activities you once enjoyed
• having problems with sleep
• experiencing changes in your appetite or weight
• feeling sluggish or agitated.

Chemical imbalances

How does SAD occur? Sunlight exposure stimulates the hypothalamus, a part of the brain that helps control your circadian rhythm — the body’s internal 24-hour sleep-wake clock.

Lack of light can throw off your circadian rhythm. This can cause your brain to produce too much of the sleep hormone melatonin and to release less serotonin, the feel-good brain chemical that affects mood. The result of this chemical imbalance? You feel low and lethargic. Other common symptoms of SAD include lack of sexual energy, overeating (especially from craving high-carbohydrate and high-calorie comfort food), and social withdrawal.

SAD affects more than just mood. It is also associated with impaired cognitive function, including problems with concentration and working memory — like having trouble recalling just-learned information or finding the right words when speaking.

People who live in the northern states, where there’s noticeably less light in fall and winter, tend to suffer more from SAD than those who live in the south. A family history of SAD or depression also raises your risk.

Drugs and light therapy

The most common drugs used to treat SAD are antidepressants. Bupropion (Wellbutrin) primarily increases levels of dopamine, while selective serotonin reuptake inhibitors (SSRIs) and serotonin-noradrenaline reuptake inhibitors (SNRIs) increase mostly serotonin levels.

If medication is not for you, or you want to avoid drugs because of possible side effects, then light therapy may be a better option. The idea behind light therapy is to replace the missing sunshine with artificial light.

Light therapy uses light boxes that produce a bright white light. As far as your brain is concerned, artificial light works just like natural sunlight. Even if you don’t yet have the clinical signs and symptoms of SAD, using light therapy during the winter may help prevent it.

There are many light boxes available online. Here are some tips for finding the right one and using it correctly.

Get enough exposure. Your light box should have 10,000 lux exposure. ("Lux" is a measure of light intensity.) A bright sunny day is 50,000 lux or more.

Don’t stare. Keep your eyes open, but don’t look directly at the light. Keep the box in front of you or just off to the side and about a foot away. Spend your time reading, meditating, or watching TV.

Get enough time. You should absorb light for about 30 minutes a day. You don’t have to do it all at once, either.

Begin in the morning. Try to get in some light time before 10 a.m.

When days become longer and sunnier, you will use light therapy less often, or may even stop during the spring and summer except for the occasional cloudy weeks.

Light therapy is relatively safe, although there can be some minor, temporary side effects like headaches and irritability.

Also, some medications, especially antibiotics like tetracycline, can make your skin more sensitive to light, and if you have a family history of macular degeneration, exposure to light therapy over the years may increase your risk. If any of these situations applies, check with your doctor before trying light therapy.

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