Dear Mark: Seasonal Affective Disorder and Light Box Therapy

With holiday fun come and gone, it’s the time of year when we all truly settle into winter. Spring is a long way off at this point. The cold and darkness aren’t going anywhere any time soon. Most people find their way through the season with a mixture of enjoyment and impatience (and maybe a warm weather vacay), but others have serious reason to dread it each year. Few of us, I think, like giving up our extra hours of daylight. The relative darkness of winter, however, presents a particularly harsh challenge to those who battle SAD – Seasonal Affective Disorder – a form of depression associated with fall and winter’s more limited sunlight.

Dear Mark,

I’m curious if you’ve done any research into the viability of full spectrum light lamps in combating SAD. I can’t get outside much during the limited daylight hours this winter and I’m noticing a marked dive in my mood – I was diagnosed as clinically depressed in college and while I’ve been able to combat it mostly through living Primally, I’m finding it especially difficult this winter (again, probably due to the fact that I really can’t go out during the day right now.) So have you done any research or know of any studies stating how harmful or beneficial these lights are, especially regarding UV rays? Thank you!


Experts believe that reduced sunlight in fall and winter throws a wrench in SAD sufferers’ circadian rhythms and disrupts their bodies’ hormonal regulation, lowering serotonin levels and/or increasing melatonin for example. Those with SAD (not to be confused with the Standard American Diet) see their everyday lives upset by symptoms such as depression, fatigue, sleepiness, irritability, and concentration difficulties. The hallmark indication of SAD is timing of course: symptoms generally begin in the fall, peak in winter, and decline in spring as daylight hours increase.

Estimates vary but suggest between 4 and 6 percent of people in the U.S. have SAD. (An additional 10-20% of us experience a less serious form of “winter blues.”) Not surprisingly, folks farther north are more at risk than those of us who live closer to the equator. Women (particularly those in their 20s-40s) appear to develop SAD more often than men, but experts don’t know why at this time.

The most common form of treatment is, as Katie suggests, phototherapy. People with SAD are generally prescribed daily use of a light box that emits bright, full spectrum light intended to mimic natural daylight. Experts usually recommend doing the daily session as soon as possible after waking up. Important features of effective light therapy include blue light exposure and total intensity (lux) power. Light boxes/lamps should be 10,000 lux (much more intense than your average home light bulb) and should include blue light for full effectiveness (PDF).

Before buying one, make sure the model you’ve chosen is specifically for SAD therapy and uses blue and not white light. Also, the model should fit the 10,000 lux recommendation – within 1-2 feet distance from the device. (Having it right next to your face for half an hour each day will get old fast.) Expect to pay anywhere from $100-500.

Light boxes do present some risks. (Doesn’t everything in life come with a “but” at some point?) Some users report eye strain and/or headache following the initial sessions, but these effects generally subside. Less common (but still generally minor) side effects include nausea, agitation, and sleep difficulties. Ultraviolet light risks, as Katie mentions, aren’t a concern for light box users because these devices are purposely designed to filter out UV rays. (UV rays are used in other light therapy uses, such as phototherapy for certain skin disorders, which is why it’s essential your model is designed for SAD.)

In recent years, however, experts have warned of risks associated with prolonged exposure to blue light. Over time, blue light can potentially cause retinal damage and macular degeneration. Because blue light appears to be an important component of light therapy for many people with SAD, redirecting the light box or using glasses that filter it might decrease the therapy’s impact. (Kind of a Catch-22, isn’t it?) Research is beginning to look at other, potentially safer options, including the use of green light.

Right now there’s no overwhelming consensus or dramatic concern for this risk. Although the light needs to be directed toward your eyes, don’t look directly at the light box. Obviously, use your light box for the prescribed time each day (and no more), and talk to your doctor before increasing your exposure time. It’s probably a good idea to see an ophthalmologist each year to assess any early warning signs for eye damage. If you’re on a medication that makes your eyes more sensitive to light, it’s especially important to talk to your doctor before beginning light therapy.

Other risks involving light boxes relate to their overuse, which can swing the neurotransmitter pendulum in the opposite direction. Excessive exposure to light boxes can result in ongoing insomnia (especially if used late in the day) or – in some cases – mania. Although a half an hour a day might be the general recommendation, the optimum treatment time will be individual.

It’s important to know that phototherapy doesn’t fully turn around depression and associated symptoms in every person diagnosed with SAD. Those who’ve been diagnosed with SAD can take advantage of other therapeutic options. Vitamin D supplementation becomes a key treatment in some folks, particularly because vitamin D levels are closely tied to direct sun exposure. Research has also shown regular exercise to be an effective therapy for every form of depression. As for conventional anti-depressants, it’s true some people with SAD find relief with them, but the side effects for these medications present their own difficulties that must be measured against their potential benefits. There are alternative depression supplements like St. John’s Wort and – an always healthy option – fish oil. (I’d suggest getting thyroid levels checked as well, since thyroid function can fluctuate from season to season.)

Finally, a study from the University of Vermont showed that cognitive behavior therapy for SAD resulted in a lower SAD recurrence rate (5.5%) the following year than either light therapy (36.7%) or combination light therapy-cognitive behavior therapy (7%). (The combination therapy, however, was significantly more effective at inducing remission of SAD [80%] than either cognitive-behavior therapy or light therapy alone [both 50%].)

For the rest of us who might wonder if we fit the “winter blues” category or who are just feeling impatient already for longer, brighter days, the same core principles hold. Get outside as much and as early as possible. When indoors, expose yourself to as much light as you can during the morning and afternoon, but curtail light in the hours before bed. Invest in some full spectrum light bulbs, which won’t offer the boost of a therapeutic light box but can offer a better option than plain incandescent bulbs. Arm your well-being with plenty of physical activity, a good Primal diet, and some wisely supplemented vitamin D and fish oil, which are both used to prevent and treat forms of depression. Find a way to enjoy the season each day, and rest assured that spring will eventually come!

Have thoughts for Katie or suggestions for light box therapy? Thanks for reading today, and be sure to share your feedback.

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

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