Abstract: Circadian rhythm disturbances parallel the increased prevalence of sleep disorders in older adults. Light therapies that specifically target regulation of the circadian system in principle could be used to treat sleep disorders in this population. Current recommendations for light treatment require the patients to sit in front of a bright light box for at least 1 hour daily, perhaps limiting their willingness to comply. Light applied through closed eyelids during sleep might not only be efficacious for changing circadian phase but also lead to better compliance because patients would receive light treatment while sleeping. Reported here are the results of two studies investigating the impact of a train of 480 nm (blue) light pulses presented to the retina through closed eyelids on melatonin suppression (laboratory study) and on delaying circadian phase (field study). Both studies employed a sleep mask that provided narrowband blue light pulses of 2-second duration every 30 seconds from arrays of light-emitting diodes. The results of the laboratory study demonstrated that the blue light pulses significantly suppressed melatonin by an amount similar to that previously shown in the same protocol at half the frequency (ie, one 2-second pulse every minute for 1 hour). The results of the field study demonstrated that blue light pulses given early in the sleep episode significantly delayed circadian phase in older adults; these results are the first to demonstrate the efficacy and practicality of light treatment by a sleep mask aimed at adjusting circadian phase in a home setting.
Alex’s Notes: I actually have an ulterior motive for talking about this study by researchers who filed a patent in the exact mask they are testing (conflict of interest anyone?). Based on a previous study that demonstrated the efficacy of a sleep mask delivering 2-second pulses of blue light every 1 minute for 1 hour on suppressing melatonin production in a laboratory setting, the researchers set out to see if similar results would be obtained with a more frequent blue light pulse, and also if this would translate into meaningful outcomes in the real world.
In the lab
Eleven young to middle-aged participants came to a lab on two consecutive Friday nights. During the entire 2-week experiment, they were asked to maintain a regular sleep/wake schedule and complete sleep/wake diaries (also for one week prior to beginning experiment) that recorded subjective bedtimes, wake times, caffeine consumption, and sleep quality.
They arrived at the lab around 10pm and were placed in a dim-lit room with red LEDs. At 11pm, each subject was asked to lie on a mattress and wear a sleep mask that delivered 120 blue-light (480nm) pulses of 2-second duration every 30 seconds for 1 hour. Blood was drawn as the sleep masked were energized (at 11pm), and again at 12pm when the subjects were woken and sent home. Counterbalancing across subjects, participants experienced a treatment night where the sleep mask was energized, and a dark control night, where the sleep mask was worn, but not energized.
On both nights, melatonin concentrations were not significantly different at 11pm. However, on the control night where the mask did not produce blue light, melatonin rose by roughly 30% within the hour. Conversely, when the mask was worn, melatonin production was suppressed by about 16%.
In the field
To see if the above results would produce anything meaningful, ten subjects averaging 70 years of age completed a 2-week field study with the same sleep mask used in the laboratory setting. During the entire 2-week period, the subjects wore a Daysimeter while awake (tool for measuring personal circadian light exposures and daily rest and activity levels), and an actigraph at all times (monitors rest/activity cycles).
The first week had the subjects lead normal lives, while the second week had them use the sleep mask which was programmed to start the blue light pulses 1 hour after bedtimes (12am) and continue for 2 hours, ending no later than 1 hour prior to the subject’s predicted core body temperature minimum (CBTmin; about 2-3 hours before natural waking). At the end of both weeks, the subjects collected their own saliva at home every 30 minutes between 6pm and 11pm for determination of melatonin concentrations. Additionally, they were asked to rate their sleepiness levels four times a day (waking, noon, dinner, and bedtime) using the Karolinska Sleepiness Scale (KSS) every day.
Dim-light Melatonin Onset (DLMO) was found to be significantly delayed after that blue light week by an average of 24 minutes. So where the average melatonin onset time was 8:27pm during the baseline week, it was 8:51pm after using the mask for one week. Self-reported sleepiness at dinner was also significantly lower after the intervention. Sleep quality and start times were not significantly different.
The authors want to emphasize that this study confirms that doubling the frequency of pulses from once per minute to twice per minute does not significantly increase the magnitude of melatonin production. They emphasize that this mask holds promise for those who suffer from circadian sleep disorders, as standard light box therapy is expensive and time-consuming.
My takeaway is the dangers of blue light around bed time. Even when we are sleeping, with our eyes shut, the blue light suppresses melatonin production. It is not as simple as going to bed, if we truly want to support our circadian rhythm, then we must make an effort to abolish all blue light around bedtime, and better yet, even before we go to bed so as not to suppress the hormone that makes us sleepy!
I don’t know, perhaps it is just me, but I feel like I was just slapped in the face by reality when I read this and realized that our eyelids are no match for blue light.