The iPad Hangover

Within the last few decades there have been massive developments in portable technology. High-powered devices have now become lightweight, convenient, and affordable. Many activities, like book reading, have been digitized. With the development of this technology, what once had been a common pastime to help get us to sleep may now actually be doing the opposite by causing a shift in our circadian rhythm for sleep.

A circadian rhythm is essentially an organism's daily internal clock. In humans it accounts for many of our physiological fluctuations throughout the day. A major molecule that affects our sleep biorhythms is melatonin. Many have heard of melatonin used as a sleep aid, and for good reason. Melatonin is a hormone that is released by the pineal gland in the brain and is involved with sleepiness and sleep regulation.

Melatonin production is heavily influenced by sunlight interacting with retinal pigments. When light hits the retina, arylalkylamine N-acetyltransferase production is depressed^[1]. Arylalkylamine N-acetyltransferase is an enzyme that catalyzes a crucial step in melatonin biosynthesis. Therefore, when light is absent, melatonin concentration builds and sleepiness ensues.

What happens when the retina is exposed to light during sleepy time hours? Research has shown that exposure to artificial light at night suppresses melatonin levels^[2] and increases alertness^[3]. When melatonin is suppressed, the body is tricked into thinking it is still daytime and the circadian rhythm can shift^[4], especially when this happens repeatedly. This shift makes it difficult to fall asleep. When a person can’t sleep due to (light-induced) melatonin suppression, that signals there has been a shift in the biological clock, relative to the normal 24-hour circadian cycle. As seen in Figure 1, levels of hormones in the body such as melatonin and cortisol fluctuate throughout the day. If the time course of one hormone is thrown out of whack, sleep and other physiological outcomes may be shifted as well.

Figure 1: Variation in melatonin and cortisol throughout the day

But why is this a problem? There is no definitive explanation^[5] as to why we need sleep, but we know that chronic deprivation is detrimental to our immune system^[6], ability to perform^[7], memory^[8], and a laundry list of other things in regard to general health.

Without question, sleep is important. In fact, chronic suppression of melatonin via evening light exposure has serious implicated health risks, such as cancer^[9]. Such conditions are frequently seen in shift-workers, like nurses and fire fighters. The International Agency for Research on Cancer, an agency directly related to the World Health Organization, has classified shift-working as a probable carcinogen. Shift work represents an extreme of altered sleep patterns, but the mechanisms behind cancer incidence due to altered melatonin secretion and circadian rhythm shifts have been widely researched^[10].

Cancer risk aside, there are other legitimate reasons to study this phenomena, as it directly relates to performance (both mental and physical) and general health. The aim of this study is to quantify the effects of light-induced melatonin suppression, caused by iPad use before sleep, on sleep quality and feelings of lingering sleepiness after waking up.

The title of this paper includes “light-emitting eReaders”, but it is important to note that the experimental arm of this study was conducted exclusively with Apple iPads.

This was an inpatient randomized crossover study that included twelve healthy individuals who had all abstained from stimulants (which was lab-verified), and were otherwise free of any disorders that affected sleep quality and sleep patterns. Three weeks before the study began, the participants adhered to a strict sleep schedule of 10:00 p.m to 6:00 a.m, which was verified by logs, call-ins, and wrist actigraphy (which measures movement patterns).

The study participants lived on the premises for the duration of the study. Sleep schedules were fixed at 10:00 p.m to 6:00 a.m.

For five days in a row, four hours before lights out, but in otherwise dim light, the study participants either:

1. Used an Apple iPad on maximum brightness
2. Read a print book

Lighting conditions were kept tightly controlled throughout the duration of the study. The iPad was at a fixed angle and distance (about 1.5 feet away) from the participants face to ensure equal light exposure between participants. Study participants were able to pick whatever literature they wanted, with the exception of comic books (possibly due to different light reflections with colorful comics) and technical reading (possibly sleep inducing). Participants remained in their beds at a fixed angle for the entirety of their reading period, except for a 15 minute break at the 2.75 hour mark.

The research group measured:

1. How long it took the participants to fall asleep and sleep activity
   • Polysomnography (PSG) was performed on nights four and five. PSG records all biophysical activity and patterns during sleep.
   • Electroencephalography (EEG) concurrently measured brain activity.
2. Melatonin levels
   • On the fifth night, blood was drawn hourly and suppression was measured by comparison to starting measurements.
3. Alertness and sleepiness
   • Self reported: participants completed a dimly-lit computer generated survey both one hour before sleep and approximately six times during their first waking hour.
   • Physical measurements: EEG was taken upon waking under reproducible conditions. Study participants were asked to be still and stare at a black dot for 3 minutes. Riveting.
4. The group measured the spectral output of several commercial e-reader devices at the same distance the face was placed from the e-reader during the time of the experiment.

Study participants adhered to a strict waking and sleeping schedule during the study. Before bed, each participant read for several hours, using either an iPad or a print book.

iPad use consistently suppressed night-time levels of melatonin, which were significantly lower than when paper books were used. In fact, reading paper books resulted in no suppression. Once the lights were dimmed, the melatonin onset peak was shifted to a later time period with iPad use when compared to paper book use. Effectively, the iPad artificially inflated the length of the “day” perceived by the brain, by about an hour and a half! This shift in circadian rhythm for iPad users happened even though the room lights were dimmed.

These changes in melatonin were associated with changes in sleep patterns of the participants. On average, the iPad users took about 10 minutes longer to fall asleep when compared to paper book readers (at around 25 minutes, compared to 15 in the paper book group).

Coincidentally, there was also a decrease of Rapid Eye Movement (REM), or dream-inducing sleep, by about the same amount of time. However, the total amount of time spent sleeping, the efficiency of that sleep (defined as the percentage of time in bed spent actually asleep), and time spent in non-REM sleep were not significantly different between groups. While the exact function of REM sleep is not fully known, one theory is that it’s involved in memory consolidation. As an analogy, computer hard drives can accumulate fragmented segments of memory after long periods of usage, and “defragmenting” the hard drive is a function of the Windows operating system to remedy that (or at least it was in the 2000s). A reduction in REM could have a multitude of impacts, including potential disruption of the blood brain barrier^[11], which is theorized to be involved in a variety of conditions such as multiple sclerosis and Alzheimer’s disease^[12].

Keeping in mind the suppressed melatonin levels and decreases in REM sleep, iPad users reported lower levels of sleepiness in the evening. EEG readings confirmed this by showing less power in the delta/theta frequency ranges (associated with sleep and drowsiness) when compared with print book readers. The following morning, iPad users were much sleepier than print readers. It took iPad users on the order of hours to “fully recover” from their sleep episode and gain full alertness after waking in the morning. Chronic use of these devices before bed may impair wakefulness, to the point where iPad users might not feel truly awake until late morning.

Data for the print book readers was essentially the opposite, with greater feelings of tiredness in the evening and increased wakefulness in the morning. This increase of tiredness in the morning experienced by iPad users is likely related to decrease in REM sleep, and might be explained by the circadian phase shift. Since the wake times were set between the groups, and the phase was shifted to a later time, the study participants who used iPads essentially woke up when their body thought they should still be sleeping. If sleep and wake times were not regulated, it’s possible that this may not have been observed. However, since most people must wake at a particular time (but not go to bed at a particular time) it’s easy to see how these issues quickly compound.

The iPad’s peak light output is in the blue range of the visible spectrum at 452 nm. The physiological effects from this blue light makes sense given the light output of human’s original light source: sunlight also peaks under 500 nm, and melanopsin pigment^[13] in the human eye absorbs in a peak range of about 480 nm. It’s not unrealistic to posit an “artificial sun” response when exposed to these higher energy photons. Even though this wavelength may not seem as bright to humans when exposed to an equal power of white light (which peaks at 612 nm), what mostly matters to the brain is the excitation of the correct eye pigments to depress the production of the arylalkylamine N-acetyltransferase, which in turn decreases circulating melatonin.

In the short term, a person may get acute sleep onset insomnia due to a shift in circadian rhythm. However, using electronic devices that emit blue light may have biological ramifications in the long term, especially since chronic melatonin suppression had been linked to an increased risk of various types of cancers. Unlike in this study, though, most people self-select their bedtimes (and to a lesser extent wake times). If a self-selected bedtime and wake time are not aligned with the body’s natural circadian rhythm, this, combined with blue-light exposure, may further exacerbate the phase-shift phenomenon and lead to chronic issues associated with sleep deprivation.

Lastly, a four-hour read time was established in this study, when many people may spend even longer times in front of a screen (either TV, computer, tablet, or phone) from afternoon to bedtime. The effects of longer exposure times are unknown, while tablet and phone displays continue to get brighter each year.

Study participants using iPads before bed took about ten minutes longer to fall asleep, experienced less REM sleep, and found it much harder to feel fully awake in the morning than people that read print books before bed.

The findings are somewhat scary for the average person who loves the Internet, which houses a vast collection of research on nutrition and health issues (and cat pictures) that can easily keep you up for hours. Back-lit tablets suppress and delay melatonin, affect EEG, negatively affect sleep quality, and hinder the ability to wake up in the morning. But do the findings of this rigorously controlled study apply to free-living humans?

At first glance, it may seem difficult to translate the data to the typical person not staying in such controlled conditions. But this is not the case. On the one hand, study participants remained in a bed (in a reclined position) for almost the entire duration of the study with an IV inserted and electrodes stuck to their heads. On the other hand, this may actually be a decent model system for the typical inactive adult.

Assuming a person works for eight hours per day at a desk (staring at a light emitting screen), sleeps for eight hours per day (but probably less) and then spends four plus hours per day using electronic devices for entertainment rather than work, it’s probably not much different than the lab setting. The study participants also had to adhere to regular eating and sleeping times. Taking these things into account, it is likely that the negative effects of this study may even be understated. This study only had people in a phase shifted state for five days, where a person may be chronically phase shifting for years. This may lead to chronic infections, general malaise, premature fatigue/overtraining, and even precursors to metabolic syndrome^[14].

The use of blue-light emitting devices is growing at a consistent rate. The use of these devices near bed time is likely to interfere with the body’s natural sleep patterns. Continued interference may lead to chronic sleep issues, which are linked to a host of negative conditions listed above. The study is not clear about how quickly this phase shifting takes place and how quickly it can be corrected. Since there are quantifiable differences between the two experimental groups, and both groups went through each condition, it is safe to say that these phase transitions can be altered over the course of days.

Take note that there is nothing uniquely bad about iPads or even tablets in general. Phones, laptops, and televisions are all devices that emit blue light at substantial levels.

Q. If I wanted to time my iPad use to avoid a phase shift, what is recommended?

If a four hour exposure (from 6:00 p.m. to 10:00 p.m.) leads to a 1.5 hour phase shift, then presumably a substantially shorter exposure time ending much earlier in the evening would lead to less phase shifting and more appropriately timed melatonin secretion. But further research would be needed to know specifics. Keep in mind that if the four hour exposure occurred much earlier, in the daytime hours, melatonin would already be suppressed by sun/light exposure and you wouldn’t have to worry.

If you have to use a tablet/laptop/phone at night, it may be helpful to dim the screen as low as possible, while still being able to read. One way to get around this is using blue-light blocking glasses, which have amber lenses and hence make you look quite silly (but also smart and innovative compared to friends/mates that may mock you.) As seen in Figure 2 these have been shown to allow for melatonin production, and hence improve sleep quality and potentially even mood^[15]. If you can’t or won’t use these glasses, but still want to use your device at night, consider free programs such as “f.lux” for laptops or other alternatives for mobile devices. These automatically make the screen dimmer and more red as the sun sets. Some apps can even lower screen brightness more than a device allows on its own.

Figure 2: Effect of light and blue-light blocking glasses on melatonin

Q. Can supplementing melatonin help to restore altered sleep rhythm?

If melatonin is used as a sleep aid in order to fall asleep during the time of maximum sleep propensity, this is plausible. Examine.com has a very extensive article on melatonin and its proper supplementation protocol. Melatonin may be an option for artificially attenuating the down-shifted melatonin peak if an iPad is used before bed. That being said, melatonin isn’t the only determinant of circadian rhythm, so artificially restoring melatonin levels probably won’t eliminate all the negative effects of bright electronic devices.

So while the specific efficacy of melatonin for phase shift caused by iPads hasn’t been researched, there is a cheaper and simpler solution. Occam’s razor dictates that the simplest answer is often correct – rather than putting a bandaid on the problem of shifted sleep, you could work on enforcing a habit of natural light exposure. Some sunlight during the day, and no bright light in the hour or more before bed. It sounds tough, but starting slow (for example, shifting device use a bit earlier each week) can make the transition easier.

The study authors noted that the relatively easier time printed-book readers had in falling asleep is actually similar to the effect size of the popular insomnia medication Lunesta. Simply constraining bright light to earlier hours could be an effective and side effect free treatment option for those with sleep issues.

Q. Should I have any issues with my e-ink device?

No, the “spectrum” of the e-ink device is comparable to a regular paperback book. However, some e-ink devices now have front-lit capacity, where light is directed on to the screen, rather than projected through it. There is no peer reviewed data on spectral emission from those devices in this study, but anecdotally some of these devices appear to have somewhat bluish hues (as opposed to the yellow of certain lightbulbs). Reading these devices on a dim brightness setting with room lights turned off may be comparable or even better than reading a print book with dim room lighting, since less of your field of vision will be lit. This has not been formally studied though.

Bulbs that can change color and brightness automatically, such as the Philips Hue, are increasingly popular. While you don’t have to go out and buy fancy smartphone-controlled light bulbs (although they are kind of cool), at least dimming your room lights at night^[16] can greatly help melatonin secretion. What about the lucky people who can sleep with lights on, maybe falling asleep to the TV or while your partner is awake? They’re not so lucky after all – sleeping with the lights on causes sleep to be shallow with more likely arousals^[17] in the middle of the night.

Even being exposed to low intensity blue light, like those blue LEDs on power cords, can make you more drowsy the next morning^[18]. So it can pay dividends to be more aware of what kind of light surrounds you throughout the evening all the way into slumber time.

Q. Will using a blue-light emitting device during the day interfere with my sleep patterns?

This is unlikely, as the mechanism of this phenomena is associated with delayed melatonin accumulation. Melatonin is at imperceptible levels during the day, so there would be no quantifiable effect of inhibiting its synthesis with blue light. The sun emits the very same wavelengths in appreciable amounts.

Most all modern back-lit portable electronic devices emit high-energy blue light. The human eye is sensitive to blue light exposure, leading to suppressed melatonin production. This suppression of melatonin production causes a shift in sleep patterns. Hence, sleeping out of line with your natural endogenous sleep patterns may lead to chronic sleep deficiency. Chronic sleep deficiency and consistently impaired melatonin production may increase the risk of many inconveniences, disorders and diseases.

While other health topics (such as low carb vs high carb) may be subject to many more studies, one of the most important but undercovered health issues may be the downstream effects of poor sleep caused by using these devices at night.