UW researchers develop more effective light therapy for seasonal affective disorder

With the days getting shorter and the rain setting in, many Pacific Northwesterners are already feeling the effects of seasonal affective disorder, or SAD. The disorder is thought to be caused by the body’s internal clock being disrupted by a lack of sunlight in autumn and winter months. Treatments include antidepressants and exposure to bright lights that mimic sunlight. As covered in OPB’s “All Science. No Fiction.,” researchers at the University of Washington have developed a new type of light therapy that could more effectively treat the symptoms of SAD.

Jay Neitz is the Bishop Professor of Ophthalmology at UW. He co-authored the study and joins us with more details.

Note: The following transcript was transcribed digitally and validated for accuracy, readability and formatting by an OPB volunteer.

Dave Miller: From the Gert Boyle Studio at OPB, this is Think Out Loud on OPB. I’m Dave Miller. With the days getting shorter and the rain setting in, many folks in the Pacific Northwest are already feeling seasonal affective disorder (SAD). SAD is thought to be caused by the body’s internal clock being disrupted by a lack of sunlight in autumn and winter. Treatments include antidepressants or exposure to bright light that mimics sunlight. But as covered by OPB’s “All Science. No Fiction.,” researchers at the University of Washington have developed a new type of light therapy that could more effectively treat this seasonal depression.

Jay Neitz is the Bishop Professor in the Department of Ophthalmology at the University of Washington. He co-authored a recent study about this and he joins us now. It’s great to have you on Think Out Loud.

Jay Neitz: It’s great to be here.

Miller: With the caveat that you’re not a medical doctor or a mental health professional, can you just give us a brief overview of what seasonal affective disorder is?

Neitz: So it’s not actually certain. As you said, this is what we think causes it. That idea does mean that it’s consistent with some of the things that work in order to prevent it. Every organism on Earth has the challenge that we live in two different environments every day. We live in an environment in the daytime where it’s light and the nighttime where it’s dark. We have to be able to deal with that. Our behavior needs to be very, very different in those two times a day. And the way organisms deal with it is that they have a clock inside of their heads. That clock dictates different behaviors during the daytime. Human beings are diurnal, so we’re more active during the daytime than during the nighttime. But it’s really important that the internal clock inside of our head is properly synchronized with the actual changing from daytime to nighttime every day.

The thought is, the clock becomes delayed, relative to Earth time, about what time it’s light and what time it’s dark. So over a period of time, as the clock becomes more and more delayed, we don’t want to go to bed at night. Our clock is telling us it’s still time to get up. But in the morning, it’s very difficult to get up. We’re groggy and we have to drink coffee and use an alarm. And as this kind of mismatch between what we have to do every day in order to function and our internal clock gets greater and greater, this is what’s believed to cause seasonal affective disorder.

Miller: How fast or slow do our internal clocks normally run compared to clock time, external human-devised, 24-hour clock time?

Neitz: The 24-hour clock time is actually devised by how long a day is.

Miller: Fair enough.

Neitz: On average, human beings’ internal clocks actually have a period, not 24 hours, but a period of about 24 hours and 20 minutes. What that means is our internal clock – of most people – tends to run slow. And it used to be that people had mechanical watches and they were pretty used to, every couple of days, resetting your clock to keep it … because most watches don’t really have exactly the same period as they’re supposed to. And now we’re not so used to that because most people use the internet to know what time it is.

So our internal clock runs slow. Really, we need to reset that clock, ideally, every single day to make it so that we make up for that 20 minutes where our clock is misset. And there is only one thing that can reset that clock, and that’s exposure to light.

Miller: What’s the best understanding for the mechanism of how it is that our body resets its own clock?

Neitz: The only access our brain has to the outdoor environment and the light is through our eyes. And we all know that we use our eyes in order to see. But there are also special cells inside of our eye that communicate directly with the internal clock inside of our head. We don’t have conscious access to the activity of those [specialized] cells. But they are cells that communicate with the clock and reset it. So that’s what’s understood, that there are these special cells.

Miller: How has light therapy for SAD typically worked?

Neitz: Circadian biology is kind of a new field. It just started back in the 1960s. People discovered that certain animals had an internal clock that could be reset by light. And it didn’t take very much light in order to do that. Then they began to do some experiments with humans and try to demonstrate that humans could reset their clocks by light. And it turns out that those attempts were not very successful, and people began to just make the lights brighter and brighter and brighter. When they got really bright – they were more equivalent to sunlight outdoors – then they were able to successfully reset people’s clocks. So it just became clear that in order to reset the human clock, it requires very bright lights.

Then people had the idea that, OK, if that’s true, and if SAD is a disorder that’s caused by a disruption of the circadian clock, then what you need to do is have a really, really bright light in order to reset our clock. The lights that were originally available cost a lot of money and they were super bright. People were instructed to get up early in the morning, sit directly in front of this giant light and stare into it for 20 minutes. But people complained [that] it was so bright, it made them squint, it gave them headaches. It was expensive and they couldn’t go about their day if they had to stay in front of this very bright light.

Miller: I remember also hearing that even the angle of the light was important. Has that been part of the standard thinking, that it has to be high enough above you to mimic a sun a little over the horizon?

Neitz: There’s some evidence for that. The idea is that the cells in our eye probably are concentrated in the lower part of our retina, so that when you’re looking up, you actually go down through your eye and are hitting this lower part of the visual field. So that’s probably true, yes.

Miller: So what’s different about the therapy that you and your fellow researchers have been looking into? What’s different than this very bright light that has been the norm since light therapy has been used?

Neitz: About 20 years ago, researchers here at the University of Washington discovered that these neurons that are inside of our eyes, that communicate with the clock, are actually color sensitive. They’re excited by either blue or longer wavelengths like yellow and orange, or vice versa. So if they’re excited by blue, they’re inhibited by orange lights or vice versa. And so they’re very sensitive to changes between blues and oranges. The question is why would the cells in our eyes that communicate with the clock be sensitive to changes from blue to orange? The answer is that, if I asked you the question outdoors – and we’re someplace where the light’s pretty bright – “What time is it?” You wouldn’t have a good idea. You might be off by many hours. It’s daytime. And the same token, if it’s dark and I said, “What time is it?” You wouldn’t know.

But if I said, right now, “The sky is shades of blues and oranges,” you’d right away [say] it’s either the sunrise or the sunset. And each of those times, the peak of sunrise and sunset, only lasts a few minutes. If you had some idea whether it was sunrise or sunset, you would actually know what time it is within some number of minutes. So it makes perfect sense that our internal clock would be sensitive to, basically, detect the sunrise and sunset. Then [we would] be able to set our clock and say, “OK, it’s sunrise, so now I’m gonna synchronize my internal clock to the sunrise or the sunset.”

Miller: So my understanding is that you have engineered an LED light that very quickly goes back and forth between these two light colors: blue and orange. How much more effective was that system in changing our internal clocks than the old standard, very bright light that was a part of SAD treatment?

Neitz: Yes, so let me just say why it needs to be so bright if it’s white. White light contains both short wavelengths like blues and long wavelengths like yellows and oranges. One of those excites the cells and the other one inhibits it. All white lights are, basically, very very ineffective at activating these neurons that communicate with our brain. So that explains why regular dimmer lights didn’t do anything. Basically, the combination of wavelengths at the same time was shutting them down.

What we decided to do, now knowing what the cells really like to see, is this alternation between blue and orange. That’s the kind of thing we want to do. What it’s mimicking is if you went out and viewed the sunrise and sunset, often there are stripes of blue and orange. And as you move your eyes around, you would see kind of alternating bursts of blue and orange. That’s what our light does.

Miller: Does it look like a constant flickering between blue and orange? That sounds unpleasant.

Neitz: Well no, it doesn’t. It turns out that these neurons inside of our head that communicate with the clock, they like to see that the blue and orange alternate very rapidly – 19 times a second. So that really doesn’t stimulate our normal color vision. So these lights maybe have a tiny, tiny bit of flicker, but it basically looks like a normal white light like you would have in your house. It doesn’t have this sense of going to blue and orange.

Miller: What do you think would happen if people used these lights all the time, morning to night, always flooding our senses with this light that gives the signal that it is either sunrise or sunset?

Neitz: So these neurons talk to a bunch of different parts of our brain, including the parts of our brain that have to do with our mood and our alertness. If we got up and looked at this light early in the morning, it would reset our clock. And once it reset, then we continued to look at it, it doesn’t reset it anymore. But it actually can help improve our mood and make us feel more energized. As long as you stopped looking at that, somewhere in the middle of the afternoon, I think you’d find that you’d be happy and productive, and your clock would be reset.

But you don’t want to look at this light into the late afternoon and evening. Because light, at that time of day, would cause a phase delay. And the commercially available bulbs are smart, and they automatically have a mode where they turn on and give you this wake up, set your clock mode in the morning. Then they have kind of an intermediate mode, and then they go to a calming mode during the late afternoon and evening.

Miller: Jay Neitz, thanks very much.

Neitz: OK, thank you.

Miller: Jay Neitz is Bishop Professor in the Department of Ophthalmology at the University of Washington.

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