Tulane Center for Circadian Biology (TCCB) researchers are co-investigators on a three-year, $1.6 million Department of Energy grant – led by John Hanifin, PhD, assistant professor of neurology, and co-investigator George Brainard, PhD, professor of neurology, at Thomas Jefferson University – to test how different types of daytime lighting – standard fluorescent bulbs versus blue-enriched LED lights – impact health and sleep quality in humans.
"Actually, it was preliminary data generated by experiments performed here at Tulane that helped to lay the groundwork for this grant," said
David Blask, MD, PhD, professor of structural and cellular biology and associate director of the TCCB.
The studies – conducted by adjunct instructor Robert Dauchy, MS – showed that mice living under lighting that is richer in blue wavelengths compared to those raised under typical cool white fluorescent light had significant beneficial impacts on their physiology and overall health.
"We here at Tulane were the first in the world to perform these experiments," said Dauchy. "In the
first study, we implanted immune-compromised rats with human prostate tumors and then placed them in either blue-tinted cages or standard clear cages," said Dauchy. The material the cages were made out of was identical; only the color of the cages was different.
Dauchy and his team exposed both populations to standard white fluorescent lighting, but as light passed through the blue-tinted cages, the animals inside received an enhanced peak of blue-appearing light. "What we saw was a huge amplification – six or seven times higher than we would normally see – in the melatonin signal at night in the animals in blue cages," said Dauchy.
"The duration of the nighttime melatonin signal was also expanded by a few hours, resulting in a prolonged biological night," said Blask. "This wasn't merely a statistically significant amplification; it was monumental!" Not only did melatonin production and duration increase, but Dauchy and Blask also saw a corresponding diminished growth and metabolism in the implanted tumors. "They were growing much more slowly in the experimental population as compared to controls, as if the animals had been treated with a melatonin supplement," said Dauchy.
"Industries around the world are currently transitioning to LED lighting," said Dauchy. LED bulbs are cost-effective because they last about 40 years, they can plug right into standard fluorescent ballasts, and they don't heat up, vibrate or produce noises like fluorescent bulbs. "And – importantly – they are enriched in the blue-appearing portion of the visible spectrum, meaning they produce a light similar to the sunlight we've evolved with outside during the daytime," said Dauchy.
The study team wondered whether there would be a measurable biologic difference between animals exposed to standard cool white fluorescent lighting – the kind commonly used in most office buildings – to those exposed to LED lamps during their normal daytime cycles.
They used three different types of study mice – two strains with genetic defects preventing or severely diminishing melatonin production and one – the C3H – with a pronounced melatonin rhythm. Half of each population was exposed to blue-enriched LED light in the daytime and the other half to cool white florescent lighting.
"We found once again that in the melatonin-producing C3H mouse, both males and females, we had remarkably amplified nighttime melatonin production that carried over into the daytime," said Dauchy. "We also saw much lower levels and more stabilized circadian rhythms of the stress hormone corticosterone, as well as metabolic biomarkers including insulin, leptin, glucose and lactic acid in the melatonin producing animals in the blue-enriched LED light environment." And the melatonin-producing animals were growing at a much more youthful rate than the control animals.
"Bob's pioneering studies provided the driving force behind the current DOE grant," said Blask. "This current project, in its simplest terms, is a human version of what Bob did with these animals."
The grant will test whether daytime LED lighting that is richer in blue wavelengths and more similar to the color spectrum found in natural daylight can improve measures of sleep, metabolism and overall health in human subjects.
The researchers designed two rigorous studies. In the first, participants will live in Thomas Jefferson University's Light Research Lab for seven days, day and night. During the day, they will live under steady fluorescent, cool or blue-toned, light conditions until bedtime. The same group will return at a later date for another seven-day stay under LED lights that are tunable: brighter and blue-enriched during the day, and dimmer and blue-depleted in the evening.
Requiring a participant to stay 24 hours a day ensures that researchers can control their light exposure very precisely, allowing them to make a stronger association between the light and changes in health status and sleep. The researchers will also measure hormones, metabolic biomarkers and aspects of sleep physiology using a wearable device that tracks movement.
A second study will look at conditions that are less controlled but more similar to the typical work environment. One group of participants will spend their day working under brighter, blue-enriched LED lighting, while another group will spend their workday in standard office fluorescent lighting. These participants will go home in the evenings and sleep in their own homes.
Dauchy and Blask will be responsible for the final phases of the study design by analyzing the participants’ blood samples for biomarkers, including glucose, insulin, leptin, cortisol, and melatonin.
"Currently, LED lighting accounts for about 30% of general lighting applications in buildings," said Blask. "It's predicted that by 2030 that should go up to about 80%. The lighting industry has touted the healthful effects of LED lighting but there has been little to no evidence to back that up. That's the point of this study. If it is true, that's incredibly important, and if it's not true, that's also incredibly important."
How does this relate to cancer? "The changes in metabolism resulting in better health for those animals exposed to blue LED lights during the day we think are really due to changes in melatonin," said Blask. "Those mouse strains with a genetic defect where they don't make melatonin didn't experience the advantageous changes even though they were exposed to the same exact conditions. For many decades, our team – which includes
Steven Hill, PhD, professor of structural and cellular biology and director of the TCCB – has been dedicated to studying the anti-cancer effects of melatonin. Our
previous work has shown that exposure to light at night suppresses melatonin production, and under those circumstances tumors develop, grow, metabolize and metastasize faster. Suppose we do the opposite. Suppose we can expose cancer patients to blue light during the day to optimize their nighttime melatonin signal, which we know is a circadian anti-cancer signal that also improves overall body and cancer metabolism. We could potentially optimally tune – just by that manipulation – their circadian system such that the cancers grow and metabolize more slowly and have less propensity to metastasize."
According to Dauchy, it all goes back to the "nature of things." "We've gotten away from how we evolved through the generations," said Dauchy. "When we were primarily an agricultural society, we were outside most of the day – being exposed to blue enriched light from the sun – and then coming in at night to almost total darkness and only being exposed to more melatonin-friendly yellow, amber or reddish light from fireplaces or candles. Now, at any time throughout a 24-hour day, we are exposed to the wrong type of light at the wrong time. We think that single issue may well be factoring into increased incidences of cancer, as well as metabolic diseases, diabetes and obesity. It's all a giant interaction with light and dark at the proper time of day."
