It’s the midst of winter, which means an estimated 10 million Americans are in the throes of Seasonal Affective Disorder. The depressive disorder—appropriately abbreviated as SAD—causes symptoms including hopelessness, sadness, fatigue, insomnia, and difficulty concentrating.
We aren’t yet sure how SAD works or what causes it, but vitamin D lamps have become increasingly popular as a possible treatment.
Does a sun-imitating lamp actually help SAD-sufferers, though? Not necessarily. In fact, doctors warn that if used incorrectly, the excess UVB rays could lead to burns or skin cancer—and that there’s already a more effective and safer treatment for SAD on the market.
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Here’s the theory behind vitamin D lamps: During the winter, you spend less time in the sun and are less exposed to the UVB rays that trigger our bodies to produce vitamin D. Vitamin D deficiencies have been linked to symptoms like pain, muscle weakness, and depression—symptoms that sound quite a bit like SAD. Those high-intensity UVB lights could stimulate vitamin D production and ease SAD symptoms.
But we don’t quite know if these vitamin D lamps work. Part of the problem is that “we just don’t know” what causes SAD, Michael Holick, a professor of medicine at Boston University, told The Daily Beast.
Holick said a promising “speculation” is that the brain makes vitamin D in the brain to regulate the enzymes that convert the precursor of serotonin—a neurotransmitter linked to feelings of well-being and happiness—into serotonin. In mice, supplemental vitamin D has been shown to boost serotonin levels. UVB rays also help the body produce endorphins, a group of hormones associated with happiness.
But the literature is inconclusive about how SAD works and can be treated. One 1999 study in The Journal of Nutrition, Health & Aging found that for seven subjects who received one month of phototherapy, there was “no significant change in depression scale measures.” (Seven patients is an extremely small sample.)
More recent studies found that vitamin D supplements did not improve depressive symptoms. Studies testing tanning beds have shown some mood improvements, but they have not been widely evaluated as a treatment for SAD.
There’s also the risk of too much UV exposure. Most vitamin D lamps clearly state that they should only be used briefly, usually for about five minutes at a time. But if a consumer didn’t follow those rules, they’d run the risk of sunburns or skin cancer, said Terako Amison, an assistant professor of clinical psychiatry and behavioral sciences at Vanderbilt University.
“Obviously UV rays have the potential to be damaging to the skin—so people have to be careful to follow the rules in terms of the distance they place between themselves and the machine,” Amison told The Daily Beast.
Amison also warned that some medical conditions—like glaucoma, cataracts, and diabetes—can be exacerbated by exposure to UV light even if the lamps are used properly. Patients with bipolar disorder should also be cautious, she said, because the light exposure could induce mania.
“If a person is going to consider [vitamin D lamps], first they need to consult with their health care professional, to get their vitamin D levels checked and see if they are deficient,” Amison said, “and if so, to have a conversation with their health care provider about if there are safer ways to replete their Vitamin D levels such as oral supplementation.”
Fortunately, there’s a more promising treatment option: bright light lamps, also known as phototherapy. These lamps—which emit light about 100 times brighter than your typical light bulb—don’t use UV rays, and are based on an entirely different theory: that seasonal affective disorder stems from a disturbed circadian rhythm.
“My recommendation has always been bright light therapy,” Holick said, arguing that “the major cause for SAD is likely your inability to suppress melatonin, because of the inadequacy of both the duration and intensity of the sunlight in the wintertime.”
When functioning correctly, the circadian rhythm works like a 24-hour internal clock that regulates sleep and wake cycles, Holick explained. When it’s dark out, the pineal gland starts producing melatonin, a chemical that makes you feel sleepy. Morning light suppresses the pineal gland, which reduces melatonin levels and makes you feel more awake.
But when there’s less light available in the winter, some people lose the ability to suppress melatonin as effectively—which can lead to persistent feelings of fatigue and depressive symptoms.
Holick and Amison say that bright light therapy—indirect light at 10,000 lux, for 20 to 30 minutes each morning—is one of the best options for patients seeking relief from SAD.
“It does work, no question about that,” Holick said. He prefers blue light therapy, which he says provides the optimal wavelength to shut down melatonin production in the pineal gland.
And while Amison said that “the gold standard for light therapy is the traditional [white] bright light box,” both types are likely “equally efficacious” when it comes to alleviating depressive symptoms.
Some evidence shows that light therapy has been a beneficial treatment.
A 2005 meta-analysis from The American Journal of Psychiatry concluded that “bright light treatment and dawn simulation for seasonal affective disorder and bright light for nonseasonal depression are efficacious.” But the analysis warned that “Many reports of the efficacy of light therapy are not based on rigorous study designs.”
A 2015 Cochrane review echoed that concern. The review scanned 91 relevant papers, but could not find a single study that was rigorous enough to be included in the review. “Given that comparative evidence for light therapy versus other preventive options is limited,” the authors wrote, “the decision for or against initiating preventive treatment of SAD and the treatment selected should be strongly based on patient preferences.” The review doesn’t invalidate the many studies suggesting the benefits of light therapy—but it does suggest that more work needs to be done.
SAD is still a mystery. But if a patient is looking for a light at the end of the winter tunnel, they should probably choose a non-UV one.
