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How to treat SAD with light therapy

John Eagles
MB ChB MPhil MRCPsych
Consultant Psychiatrist
Royal Cornhill

For thousands of years, the effects of the seasons on our health and wellbeing have been recognised. Long before that, human beings may have benefited from going into a state of mild hibernation in winter and emerging, full of energy and vigour, in spring.(1)  Procreating in the spring or summer would have been advantageous, with children born in the following late winter/spring when better weather and more plentiful food supplies could be anticipated. Beginning to sleep and eat more as autumn approached would help to preserve energy and, for pregnant females, engendered advantages to both mothers and babies in utero. It is quite possible that seasonal affective disorder (SAD) constitutes the continuing symptoms of this attenuated hibernation, which was once an evolutionary advantage for Homo sapiens.

Symptoms of SAD
Recurrent episodes of affective disorder, occurring on a seasonal basis, are (perhaps self-evidently) the central feature of SAD. Typically, the episodes start in October/ November and remit in March/April. People with SAD are very often at their worst in January and February. Following remission in the spring, about a third of people suffering from SAD become mildly hypomanic; they are cheerful, overactive, extrovert, exuberant and have a reduced sleep requirement.
Many of the winter symptoms of SAD are shared with the picture of nonseasonal depression. These shared symptoms include:

  • Low mood (often worse in the morning).
  • Anergia.
  • Reduced activity.
  • Low libido.
  • Social withdrawal.
  • Irritability.
  • Anxiety and loss of interest/pleasure in previous activities.

It is more likely that fatigue will be described before low mood than would be the case in nonseasonal depression, and there are winter symptoms that are fairly specific to SAD:

  • Hypersomnia, with severely affected subjects feeling that they could sleep for 16 hours per day or more.
  • Daytime somnolence, often peaking in the late afternoon.
  • Increased appetite, often specifically for chocolates and/or carbohydrates.
  • Weight gain.

It adds credence to the diagnosis of SAD if people make a complete recovery from their symptoms during spring and summer.
Among sufferers of recurrent mood disorders, a recent study found that SAD was markedly under-diagnosed.(2) This is unfortunate given the effectiveness of treatment and underlines the importance of vigilance for the diagnosis in both primary care and psychiatric settings.

Estimates of the prevalence of clinically moderate to severe SAD in the UK average at around 3% of the population. However, many of us will recognise several of the winter symptoms mentioned above to some extent in ourselves. A study in the USA found that some degree of seasonal change in wellbeing occurred in 90% of the respondents.(3) It is important to appreciate that the symptoms of winter depression occur across a spectrum of severity; mild symptoms merit simple self-help measures, and only at the more severe end of the spectrum is light therapy and/or antidepressant medication required.
Females in the reproductive years are most susceptible to SAD. Moving to live at a "darker" latitude,  further away from the equator, also confers an increased risk of suffering from winter depression.

Some principles of management
Understanding that winter symptoms arise through reduced light levels, and reduced daylight is clearly important. It is also usually helpful to appreciate that symptoms exert "knock-on effects" upon each other. For example, SAD sufferers generally cease exercise in winter, contributing to further lethargy and weight gain, giving rise in turn to further despondency, increasing social withdrawal and so on. Targeting any of these symptoms will thus have a beneficial effect on other problem areas. For example, walking outside each day in winter can have the beneficial effects of exercise, daylight exposure, combating social withdrawal and reducing weight gain. Supportive psychological measures are usually helpful; sufferers should be reminded that their symptoms will remit, and it is often helpful to focus on the shortest day as a "winning post", whereafter spring is on the way.

Light therapy
The self-help measures mentioned above should be used initially and continued in tandem with other treatments. Light therapy (and/or an antidepressant) is indicated for people whose winter symptoms are sufficiently severe to cause significant disruption to their functioning, most notably in the areas of relationships and employment/childcare.
Light therapy works by replacing the "missing" light during the dark months of the year, and using it in the morning sends a message to the brain (via the pineal gland) that: "it's a bright sunny morning, lets get up and get going". This is the explanation I give to patients. At a more neurochemical level, some people will like to know that light therapy almost certainly acts by raising levels of brain serotonin, as many antidepressants do.
Therapy is usually provided by a lightbox, which mimics sunlight with the ultraviolet wavelengths removed. If tolerated, lightbox users aim for a brightness of up to 10,000 lux. This means getting quite close (about 20 inches with the average box) to the light source, while appreciating that brightness is related to the square of this distance. That is to say, if one moves twice as far away one receives only one-quarter of the brightness. The usual "starting dose" is 10,000 lux for 30 minutes each morning around breakfast time. There is good evidence that light therapy works better at breakfast time than later in the day.(4)
For some people with SAD, waking up and getting up on winter mornings constitute their greatest problems. These people may need their lightbox beside their bed to use while they "come to". Alternatively, they can use a dawn-simulating alarm clock. These come on at low illuminance 30-90 minutes before usual wakening time, gradually increasing in brightness. Perhaps because they may improve treatment adherence, one study found dawn-simulating alarm clocks to be more effective than lightboxes for the symptoms of winter depression.(5)
Significant side-effects from light therapy are fortunately not very common. Transient headache or blurred vision occur in up to 20% of lightbox users. Light therapy can cause mild agitation - an indication to reduce the dose - and can give rise to insomnia when used too late in the day.
Lightboxes usually retail at £100-250. However, many suppliers provide a three-week sale or return service. This is quite long enough to gauge effectiveness, since the speed of onset is fairly rapid. If light therapy is going to prove effective, most people are feeling more energetic and cheerful within the first week of treatment.


  1. Eagles JM. Seasonal affective disorder: a vestigial evolutionary advantage? Med Hypoth 2004;63:767-72.
  2. Shin K, Schaffer A, Levitt AJ, Boyle MH. Seasonality in a community sample of bipolar, unipolar and control subjects. J Affect Disord 2005;86:19-25.
  3. Kasper S, Wehr TA, Bartko JJ, Gaist PA, Rosenthal NE. Epidemiological findings of seasonal changes in mood and behavior. Arch Gen Psychiatry 1989;46:823-33.
  4. Lewy AJ, Bauer VK, Cutler NL, et al. Morning vs evening light treatment of patients with winter depression. Arch Gen Psychiatry 1998;55:890-6.
  5. Avery DH, Eder DN, Bolte MA, et al. Dawn simulation and bright light in the treatment of SAD: a controlled study. Biol Psychiatry 2001;50:205-16.

Seasonal Affective Disorder Association

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