Melatonin Disruption Seen With Self-Luminous Tablets

Nancy A. Melville

September 12, 2012

September 12, 2012 — Light emanating from self-luminous tablet computers can suppress levels of the sleep hormone melatonin, potentially having a negative effect on the body's circadian rhythm, new research suggests.

Researchers with Rensselaer Polytechnic Institute's Lighting Research Center in Troy, New York, have previously explored the effects of light from computer monitors and 70-inch televisions but found little to no suppression of melatonin.

But the availability of tablet devices raise new concerns, not only because they emit optical radiation at short wavelengths near the sensitivity for melatonin suppression but also because they are often viewed for hours on end and at close range, said lead author Mariana Figueiro, PhD.

"The main issue with tablets and computer screens, and less of an issue with TV, is that the device is placed close to the eyes, so light at the back of the eye, which is what matters for the circadian system, is increased with proximity of the source," said Dr. Figueiro, an associate professor and director of the LRC Light and Health Program at the Lighting Research Center.

Their findings were published online July 31 in Applied Ergonomics.

Participants viewed tablets without goggles, through orange-tinted goggles capable of filtering out radiation that can suppress melatonin, and through clear goggles fitted with blue LEDs to suppress melatonin.

Nocturnal Melatonin

In a small study to investigate how self-luminous tablet display screens affect nocturnal melatonin, Dr. Figueiro and her colleagues measured melatonin suppressions in 13 participants after exposures to backlit tablet devices (Apple iPads) viewed under 3 experimental conditions.

Under one condition, the tablets were viewed through a pair of clear goggles fitted with 470-nm (blue) light from light-emitting diodes (LEDs), which served as a "true positive" condition because the blue light is known to be a strong stimulus for suppressing melatonin.

Under the second condition, the tablets were viewed through orange-tinted glasses that filtered out the short-wavelength radiation, representing a "dark control" condition. In the third condition, no glasses or goggles were worn.

The iPad display is approximately 9.7 inches diagonally and is backlit with LEDs. The tablets in each viewing condition were set to full brightness.

Each of the participants also wore dimesimeters, small light meter devices that were developed at the RPI Lighting Research Center. The devices are worn near the eye and continuously record circadian light and activity levels.

Although the results showed no significant melatonin suppression after 1 hour of normal exposure, the suppression after 2 hours was significantly greater than 0 (P = .006).

"Our study shows that a 2-hour exposure to light from self-luminous electronic displays can suppress melatonin by about 22 percent," the authors write.

The dimesimeter measurements indicated that the level of photopic illuminance from tablet use can vary significantly according to the type of task being performed and the distance from the device to the eyes.

Illuminance levels ranged from 5 lux, which would typically not affect melatonin levels, to 50 lux, which could have a significant effect over 2 hours.

Type of Task

"The type of task will influence the color of the background," Dr. Figueiro explained. "White background, such as with Microsoft Word documents or Facebook, emits more light than darker backgrounds, like movies or black screen with white fonts. And for the same light being emitted by the device, the farther from the eye, the least amount of light at the retina."

Teens and adolescents may be particularly prone to the melatonin-suppressing effects of tablet device usage, and not just because they are known to be heavy users, Dr. Figueiro noted.

"Studies suggest that adolescents are more sensitive to light in the evening and will respond more to an evening light," she said. "Having said that, the effect can occur in any population."

Melatonin onset occurs approximately 2 hours before natural bedtimes, Dr. Figueiro explained. "If one suppresses the onset of melatonin in the evening, it will delay the timing in which the biological clock will tell the body to fall asleep."

By disrupting normal sleep patterns, the suppression of melatonin has been implicated in other health issues, including an increased risk for obesity and other serious disease, such as breast cancer.

One easy solution is for tablet users to adjust the brightness of their devices at night to allow less interruption with normal circadian rhythms.

Dr. Figueiro and her colleagues also suggest the potential development of more "circadian-friendly" electronic devices.

"Since a large portion of the population spends most of their waking hours in front of a self-luminous display, it is important that manufacturers and users have a tool to increase or to decrease circadian stimulation delivered by their self-luminous displays," they write. "However, it is also important to consider how and how long these devices are used."

A Real Concern

Asked to comment on these findings, William Kohler, MD, a spokesperson for the American Academy of Sleep Medicine, pointed out that melatonin is key in regulating the body's circadian rhythms, and the ability of light from handheld or close-range electronic devices and tablets to disrupt melatonin is indeed a concern.

"The concern is that the bright light inhibits the production of melatonin, which acts on the suprachiasmatic nucleus, a group of neurons in the anterior hypothalamus. This is basically our pacemaker and allows us to be alert," explained Dr. Kohler, who is director of the Florida Sleep Institute in Spring Hill.

The findings offer some early insights into the potential effect the devices can have on sleep patterns, he added.

"It was interesting that the researchers did show the melatonin was suppressed not only with the bright light, but also the duration and the type of light."

"But we're in a virgin field of expanding knowledge right now, and it's exciting because almost every week there is new research coming out on therapies for sleep problems."

The study was funded by Sharp Laboratories of America. Dr. Figueiro and Dr. Kohler have disclosed no relevant financial relationships.

Appl Ergon. Published online July 31, 2012. Abstract