Humans, like most animals, are affected by sunlight or the lack of it, both physically and emotionally. But some people are affected much more than others. During the shorter, darker days of late autumn and winter, especially in more northern regions, they may experience a type of clinical depression called seasonal affective disorder (SAD), which can be likened to the general winter malaise and lethargy that many of us experience but is more severe and debilitating.
People with SAD feel hopeless for no evident reason, lose interest in people or things they normally enjoy, are fatigued and unproductive, have difficulty concentrating, sleep too much, and find it hard to get out of bed. They tend to eat more (especially carbs), which, together with less physical activity, often leads to winter weight gain. Then in the spring or early summer, they recover.
Even though SAD goes away on its own when the days get longer, it can last a full five months, which is a long time to be miserable. Fortunately, there are several ways to treat and possibly even prevent it, notably light therapy, though there’s no one-size-fits-all treatment. If you have symptoms like the ones mentioned above, it’s important to consult your doctor or a mental health professional. Don’t try to self-diagnose and self-treat. In the meantime, here are answers to some basic questions about SAD.
How many people have SAD?
The most commonly cited figure is 5 percent of Americans, on average, though estimates range from 1 to 10 percent, depending on the populations surveyed and criteria used. At least two-thirds of sufferers are women, who are also more prone to nonseasonal depression. In addition, many more people have a milder, shorter-lasting form of SAD often called the “winter blues” (technically known as subsyndromal SAD).
The symptoms of SAD usually start during early adulthood and tend to decline in older age. Its incidence rises at higher latitudes—that is, with increasing distance from the equator, north or south. Thus, only 1 percent of Floridians may suffer from SAD, versus 10 percent of Alaskans.
SAD often runs in families, and several genetic factors have been proposed to help explain this. It also occurs more frequently in certain ethnic groups. For instance, while SAD rates are high in Scandinavia, they are low in Iceland, which is also far north. And a 2013 study focusing on the largest immigrant groups in Norway found that those from Iran had a much higher rate of wintertime SAD than those from Sri Lanka.
How can SAD be distinguished from other forms of depression?
They are identical, except for SAD’s timing. Rather than a unique diagnostic condition, SAD is simply seasonally recurring depression. According to the standard definition, people have SAD if they’ve had a seasonal pattern of depressive episodes for at least two years, with no other explanation for the mood changes and no nonseasonal episodes, and they’ve had this general pattern of depression in some previous years as well.
What causes SAD?
Researchers have been studying SAD for more than three decades. They have proposed several mechanisms to explain how light deprivation during winter may cause depression, though it’s unclear why this affects some people much more severely than others.
Light deprivation can disrupt the body’s internal clock (circadian rhythm), which responds to environmental cues, notably light and darkness. With longer periods of darkness, the body’s production of melatonin increases; this hormone induces sleep and influences mood.
Light deprivation also affects levels of certain neurotransmitters (such as serotonin), which help regulate mood, energy, and appetite. Even variations in retinal sensitivity to light may play a role in some people.
How does light therapy work?
It attempts to replace the missing daylight and replicate its effects in the body—for instance, reducing melatonin production. Typically, you sit about 12 inches from a special light box, positioned above eye level, first thing in the morning for about 30 minutes.
The device emits a controlled amount of light (usually cool white light), much brighter than ordinary lamps and with a filter for ultraviolet rays.
The light shines into your open eyes, but you don’t look at it; you can read or do work.
Most people with SAD experience an antidepressant effect within a few weeks, though some respond after the first session—while others get little or no benefit. Light therapy must be done every day, well into spring. If you know it helps, you can start doing it in the fall before SAD sets in, as a preventive measure.
The timing and dosing of light should be tailored to your circadian rhythm (and other factors) by a mental health professional who is knowledgeable about the therapy and can recommend specific light boxes. That’s important, since the devices are available without a prescription and are not regulated by the FDA—and their marketers make many confusing claims. Some are approved by Underwriters Laboratory (UL), which tests and certifies consumer products for safety, though not for effectiveness.
Light therapy is generally safe, but when used incorrectly it may cause agitation, headaches, eyestrain, and nighttime sleeplessness. People with bipolar (also called manic-depressive) disorder or eye diseases should, in particular, get expert advice before starting light therapy.
The nonprofit Center for Environmental Therapeutics provides advice about how to select light boxes, which you can discuss with your health care provider. The devices generally cost $150 to $300.
Are there different types of light therapy?
Some lamps emit blue light as well as white light, which further reduces melatonin production and increases alertness. It’s not clear if this is superior, and there are concerns about potential eye damage. “Dawn simulators” gradually turn on light in the morning to awaken you, in an attempt to reset your body clock. Research on them has been limited and inconclusive.
Light-emitting visors are also marketed for SAD, but there’s no convincing evidence they are effective. Even more questionable is Valkee, a small Finnish device marketed for SAD that looks like an iPod with earbuds and projects light into your ear canal. Not surprisingly, a small 2013 study found it to be no more effective than a placebo device.
What about antidepressants?
Limited research has found that SSRI antidepressants, which act on serotonin levels in the brain, are effective in some people with SAD. The small placebo-controlled studies used fluoxetine (brand name Prozac) or bupropion (Wellbutrin); the FDA has approved bupropion specifically for SAD. Still, because these drugs can have adverse effects, light therapy remains the first-line treatment.
Will therapy or counseling help?
Short-term cognitive behavioral therapy (CBT) has been found to be beneficial in studies on people with SAD. The cognitive part helps identify and then reframe recurring negative thoughts, attitudes, and expectations that exacerbate symptoms.
The behavioral part of CBT identifies pleasurable ways to help people get out every day and feel better, such as having lunch with friends, going out for a walk, or doing volunteer work. It’s not as easy as it sounds for people deep in depression. One study published in 2009 found that six weeks of CBT (twice a week) worked as well as light therapy, and that it had a carryover benefit the following winter.
Can vitamin D supplements or tanning beds prevent or treat SAD?
Studies testing vitamin D supplements for depression have had inconsistent or inconclusive results. Blood levels of D drop in the winter because the skin produces it only when exposed to ultraviolet rays from strong sunlight, and it’s tempting to think that the vitamin may play a role in wintertime depression. Research has indeed linked low vitamin D to depression in general, but it’s unclear whether it is a cause or effect of depression—or just a marker for spending little time outdoors.
Unlike properly designed SAD light boxes, tanning beds emit ultraviolet rays and thus boost vitamin D production, but should not be used because of the risk of skin cancer.
What about simply getting more daylight?
That may be all you need to do for milder forms of seasonal depression. But if you have been diagnosed with SAD, it’s unlikely to be enough, since winter light is weak. Still, it may help as an adjunct to the treatments mentioned above. Try to maximize your daylight exposure by getting up and out early, exercising outdoors, making your house brighter, sitting near windows on bright days, and taking a winter vacation in a sunny locale, if possible.
Published December 15, 2014