Melatonin and Seasonal Affective Disorder

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Melatonin and Seasonal Affective Disorder

Consistently, research into seasonal affective disorder (SAD) has found impairment in melatonin synthesis in the brains of people with the condition1. Melatonin is released by the pineal gland in response to darkness and it causes drowsiness.

Among those with SAD, production of melatonin in response to darkness is delayed, which results in higher levels of the hormone during the day. This has lead researchers to point an accusative finger at melatonin as a possible cause.

However, there are problems with this assumption. For example, research into light therapy (a common treatment for SAD) conducted by Lewy, Sack, and Singer at the Oregon Health and Science University found that melatonin levels do indeed return to normal levels after light therapy. But, 30% of people with SAD don’t respond to it, even though their melatonin levels returned to normal. There is no improvement in their symptoms which puts a big question mark over the relationship between melatonin and seasonal affective disorder.

A study of 68 participants (34 receiving melatonin and 34 receiving placebo) conducted by Lewy, Lefler, Emens, and Bauer in 2006 hoped to solve the issue of non-response to light therapy3.

Lewy found that people who don’t suffer from SAD have a six-hour interval between the time the pineal gland begins to secrete melatonin and the middle of sleep. This interval for people with SAD is either longer or shorter than six hours.

Test subjects with shorter intervals were given melatonin in the afternoon, and people with longer intervals were given melatonin in the morning. These subjects were compared to a placebo group and people who took the melatonin at a random time. When the hormone was taken at the right time (i.e. the groups matched to their interval), subjects had significantly less depressive symptoms than the comparison groups. This outcome may account for the results found among non-responders and the lack of effect amongst the larger sample size. Based on this result, evidence exists for a complex relationship between melatonin and seasonal affective disorder.

Facts about Seasonal Affective Disorder

  • Seasonal affective disorder symptoms include depressed mood, fatigue, loss of interest in sex, oversleeping, weight gain. and an increased appetite for carbohydrates1
  • Estimated rates of seasonal affective disorder vary from between 4-10%
  • Incidence increases as hours of sunlight decrease during the winter months
  • Women suffer from seasonal affective disorder more than men
  • There is also a mild subsyndromal type of seasonal affective disorder often referred to as S-SAD
  • When the two mild and normal types are included together, the incidence may increase to 21% of the United States population


1. Miller AL. Epidemiology, Etiology, and Natural Treatment of Seasonal Affective Disorder. Alternative Medicine Review, 2005; 10 (1), 5-13.

2. Lewy AJ, Bauer VK, Cutler NL, and Sack RL (1998). Melatonin treatment for winter depression: A pilot study. Psychiatry Research, 1998; 77: 57-61.

3. Lewy AJ , Lefler BJ, Emens JS, and Bauer VK. The circadian basis of winter depression. Proceedings of the National Academy of Sciences USA 2006 April 28th.