MEDICAL MATTERS:Can light therapy relieve symptoms of Sad, writes MUIRIS HOUSTON
AT THIS time of year, a number of patients will mention the evenings closing in and how it makes them feel like hibernating. They don’t feel depressed or lethargic, but they are aware of a natural tendency of going to bed a little earlier and sleeping a little longer. It’s not that they have seasonal affective disorder (Sad) – although that possibility must always be considered – rather it is an elemental expression of the daily and seasonal rhythms embedded in all animals.
Meanwhile people with Sad experience typical depression symptoms, such as low mood, energy loss and fatigue, as well as some atypical features, including a desire to sleep for longer, increased appetite and weight gain, all of which have a seasonal onset. Episodes of Sad typically last about four months; about 60 per cent of sufferers will experience annual bouts of illness, with a minority lucky enough to go into complete remission within several years.
What causes Sad? Genes that affect our metabolism of the neurotransmitter serotonin are implicated. Melatonin, a hormone secreted by the pineal gland during darkness, also has a part to play. This hormone is central to the regulation of our circadian (daily) rhythms and our circannual (seasonal) ones.
Researchers from Yale University have carried out some work that suggests people with “winter depression” or Sad experience a significant phase, or shift in their circadian rhythms. Most commonly the normal phases are delayed, although for some people with Sad they may be advanced. This has led to the use of both light and melatonin as phase-resetting agents for affected patients.
Although its mechanism of action is still unclear, it has been shown that blood levels of melatonin, which may be abnormally high at certain times of the day, are rapidly reduced by light exposure. Depending on when bright light is used, the body’s internal clock shifts ahead or is delayed when stimulated by light. These physiological time shifts could be the reason for a therapeutic response. On the other hand, the antidepressant effect may not involve rhythm shifts at all but rather overall changes in neurotransmitter levels.
Proponents of light therapy, which has been in clinical use since the 1980s, say patients should notice a marked improvement in symptoms within four or five days; symptoms often return in about the same amount of time when the lights are withdrawn. Some people take longer than the usual few days to respond to light, and so it may be worth persevering for a week or two before concluding that it doesn’t work. Most users maintain a consistent daily schedule of light exposures throughout the winter months. The usual “dose” involves 30 minutes of daily exposure to 10,000 lux light, generally in the morning.
Side effects of light therapy are usually mild: they include eye strain, headache, agitation and sweating. Reducing the dose of light may help these effects subside. And if you have pre-existing eye disease, such as macular degeneration or diabetic retinopathy, it’s best to get medical advice before purchasing a light-therapy box.
Various guidelines for Sad differ in their view of the role of light therapy. The American Psychiatric Association recommends light therapy as a time-limited trial in people with mild to moderate seasonal depression. In the UK, guidelines from the National Institute for Health and Clinical Excellence are more circumspect: they propose that patients with winter depression who wish to try light therapy in preference to antidepressant or psychological treatment should be advised that the evidence for its efficacy is uncertain.
A review in the reliable Drugs and Therapeutics Bulletin, noting the difficulty in comparing trials of light therapy, has the following advice: “Bright light therapy in the early morning, using a light box or dawn simulation, appears to be a reasonable first-line approach to relieve depressive symptoms, instead of, or as well as, drug therapy and/or cognitive behavioural therapy (CBT) when the patient has mild or moderate symptoms; people with more severe symptoms should be treated with antidepressant drugs, with or without light therapy or CBT.”