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San Diego Scientist Illuminates Link Between Light And Health

Evening Edition

Above: We all know that proper diet, exercise, and sleep can improve our health. But emerging research suggests we might want to consider something else, too. Something so ubiquitous, few of us ever stop to reflect on it. That something is light. KPBS science reporter David Wagner profiled one San Diego researcher who's illuminating the importance of getting light in the right amount at the right time.

Aired 8/7/14 on KPBS News.

Whether it's coming from the sun or a smartphone, light is abundant. But research suggests the wrong light at the wrong time of day can disrupt the body's natural rhythms.

Satchin Panda feels at home in the Salk Institute. Not just because of the prestige, but also because of Salk's unique architecture. 

"They built this institute with big glass doors and windows," Panda said.

At every turn, the building emphasizes one of Panda's abiding research interests: light. His lab sits two stories below the ground floor, but thanks to Salk's deep natural light wells, it's anything but dark and gloomy.

Floor-to-ceiling windows provide abundant natural light in Satchin Panda's lab, July 18, 2014.

"There is very little lab space inside that's not brightly illuminated," he said.

Panda grew up in India. And he can remember visiting villages back when they still didn't have electric light.

Now, he studies circadian rhythms. He's trying to understand how our biological clock keeps our bodies on a steady 24-hour cycle that determines when we eat, when we work, and when we sleep. 

And he's found that light plays a crucial role. But it's not necessarily the light we see. Even blind people have their daily rhythms regulated by light.

"That told us that there might be some unknown light sensor present in the eye," Panda recalled.  

That light sensor is called melanopsin. Panda knows it helps keep the body's internal clock ticking, because he once did an experiment on mice that lacked melanopsin.

The mice could see normally.  But when Panda simulated jet lag for the mice by adjusting the time of day when they were exposed to light, things got rough.

"A normal mouse would readjust to the day-night cycle within a week. But this mouse would take almost a month to adjust. And that was really fascinating because this mouse can see perfectly fine, but the light sensor that was resetting its clock was not there." 

Without melanopsin, the body struggles to intuitively know when it's time to wake up, and when it's time to sleep. That's because melanopsin plays an important role in regulating melatonin, a hormone that promotes sleep.

Satchin Panda at the Salk Institute, July 18, 2014.

Light helps keep melatonin down during the day. When light floods the melanopsin in our eyes, our body dials back on the hormone, keeping us alert. 

At least, that's how things should work. But the way Panda sees it, this system is getting hijacked by the typical 21st century lifestyle. 

"Nowadays, with artificial light, and with so much work to do, we constantly stay awake late into the night," Panda said.

We spend all day working indoors, shielded from natural light. Then we spend our nights bombarded with the bright displays of laptops and TVs and smartphones. 

"The question is, how does this lifestyle affect our clock on a daily basis, and whether this effect will guide our bodies on the way of health or disease in the long-term," he said.

There's reason to think we could be harming our health with all these wrong light signals at all the wrong times. Just look at medical data on workers who alternate between daytime and graveyard shifts, living totally out of sync with the natural light cycle.

"What has been shown is, shift work predisposes to quite a few chronic diseases," said Panda. "Like obesity, diabetes, certain kinds of cancers, and even dementia." 

Katie Schoolov

A Fitbit-like device that measures movement and the amount of light the wearer is exposed to.

But Panda says more data is needed to really drill down on the way light affects health. So he's getting people to wear light sensors around their wrists. 

"The whole idea is to see how much light you get exposed to during the entire day," Panda explained. "And we'll see whether that light level will affect how you are sleeping, how much you are active."

The idea of a Fitbit for light intrigued me, so I took one of Panda's sensors home. And I went about my routine, working, sleeping, running errands.

Ten days later I went back to Panda's lab to get the rundown on my light diet. Panda brought up a graph with bright yellow bars tracking my daily light exposure. 

Katie Schoolov

A graph showing David Wagner's light exposure and movement as measured by a device used in Satchin Panda's research.

The first thing I noticed was that I get very faint light when I'm in the office. A few yellow peaks mark my commute into and from work, but my chart is mostly dim, poorly lit valleys. There was one outlier, though: a day when I worked mostly outside.  

"You look at this day, then look at the sleep that night. You have very little hand movement in bed, so that means you were sleeping like a baby," Panda said. 

He said little-by-little, people are becoming more conscious about the link between light and health.

Some people now use light therapy to treat their depression. And developers are making software that filters out bright light from computer displays at night to help the body's melatonin production. He'd like to see architects fill offices and other buildings with more light.

"People who are building these structures, are they factoring in what we are now learning from the effect of light on human behavior and health?" 

If you can't bring the workers outdoors, Panda says maybe we can figure out a better way to bring the outdoors in for the workers. 

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