Cognitive behavioral therapy may be better at treating seasonal affective disorder than light treatment, according to research published in the American Journal of Psychiatry.

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SAD causes depression in the winter months.

Seasonal affective disorder (SAD) is a form of depression that affects over 14 million Americans, ranging from 1.5% of the population in southern states like Florida to over 9% in the northern regions of the country. An estimated 10-20% of all cases of recurrent depression follow a seasonal pattern.

SAD has been known for over 150 years but was not officially named until the early 1980s.

It is believed to be caused by a hormonal imbalance triggered during the shorter days of winter. In people with SAD, the late winter sunrises interfere with circadian rhythms and cause levels of the sleep hormone, melatonin, to remain high into the morning. This results in fatigue and depression.

The symptoms include fatigue, weight and appetite changes, oversleeping, loss of interest in hobbies and social activities, difficulty concentrating and low mood. Feelings of anxiety and irritability may also occur, as well as difficulty concentrating, remembering details and making decisions.

Light therapy has been considered the gold standard for treating SAD. It involves timed, daily exposure to bright artificial light of specific wavelengths using a light box. However, according to the National Institutes of Health (NIH), nearly 50% of people do not respond to light therapy alone, so it may be combined with cognitive behavioral therapy (CBT) and antidepressant drugs.

Fast facts about SAD
  • SAD affects 6% of Americans
  • Women are more likely to be affected than men
  • January and February are the most difficult months.

Learn more about SAD

A team led by Prof. Kelly Rohan, of the University of Vermont, started by studying 177 participants using light therapy for 30 minutes each morning at home for 6 weeks. The duration was adjusted over time to maximize response and reduce side effects.

Some participants then continued the daily light exposure at home until spring and were offered access to a light box again the next winter.

The others received a special form of CBT twice a week for 50-minute sessions over 6 weeks. The CBT sessions taught them to challenge negative thoughts about dark winter months and resist behaviors like social isolation that affect mood.

In the first winter after the initial treatment, both groups reported comparable relief from seasonal depression. Both treatments effectively appear to reduce the depressive symptoms of SAD, with no statistically significant differences between them.

By the second winter, nearly 70% of light therapy subjects had given up on the light treatment.

Depression recurred in 46% of those using only light therapy, compared with 27% of people in the CBT group. Depressive symptoms were also more severe for those in the light therapy group.

It seems that light therapy is more effective at addressing acute episodes, while CBT is more likely to prevent relapse in future winters.

Prof. Rohan says:

Light therapy is a palliative treatment, like blood pressure medication, that requires you to keep using the treatment for it to be effective. Adhering to the light therapy prescription upon waking for 30-60 minutes a day for up to 5 months in dark states can be burdensome.”

CBT, meanwhile, is a preventive treatment. Once its basic skills are learned, the impact will last, giving a sense of control over symptoms.

The researchers suggest that given that the difficulty in persisting with light therapy, and the large number of Americans suffering from the recurrent disorder, CBT may be the better treatment option in the long term.

Medical News today has previously reported on a possible link between SAD and changes in serotonin levels.