Sleep health

Blue light may not affect your sleep-wake cycle, study finds

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Researchers say that blue light may not significantly affect a person’s circadian rhythms. AleksandarNakic/Getty Images

  • Blue light from the sun is vital in regulating a person’s sleep-wake cycle.
  • New research suggests that blue light does not affect a person’s “internal clock.”
  • The findings further our understanding of the effects of light on sleep quality and duration.
  • Previous studies have shown that blue light from devices can damage the eyes and negatively impact sleep.

Of the seven colors in the visible light spectrum, blue lightTrusted Source is the one most people know and talk about.

The majority of light coming from the sun is blue light, making it vital in helping to regulate a person’s sleep-wake cycle.

However, blue light is also the type of light emitted by computer screens, smartphones, tablets, and LED televisions.

Previous research shows that too much exposure to blue light from technology devices can potentially damageTrusted Source the eye’s retina, lead to digital eyestrainTrusted Source, and negatively affect sleep quality and durationTrusted Source.

Now, a new study by researchers at the University of Basel in Switzerland suggests that blue light may not affect a person’s “internal clockTrusted Source.”

The study was recently published in the journal Nature Human BehaviourTrusted Source.

How does light affect circadian rhythm?

Ganglion cellsTrusted Source are a type of photoreceptor in the eye that plays a role in the sleep-wake cycle.

The other two photoreceptors in the eye — rods and cones — convert light coming into the eye into electrical signals relayed to the brain, providing vision.

First study author Dr. Christine Blume, a psychologist at the Centre for Chronobiology of the University of Basel in Switzerland, explained to Medical News Today:

“In humans, the main effect of light on the internal clock and sleep is mediated via specialized light-sensitive ganglion cells in the retina, which are maximally responsive to short-wavelength light around 490 nanometres. This was well-established even before our study. However, there was reason to believe that the color of light, which is encoded by the cones, could also be relevant for the internal clock, because also cone-signals serve as an additional input to the internal clock. The question was, whether this input is also relevant.”

Effects of blue light vs. yellow light on sleep

For this study, Dr. Blume and her team recruited 16 human participants who were exposed to a blueish light, a yellowish light, and a white control light for one hour before bedtime.

Researchers designed the lights in a way that they activated the color-sensitive cones in the retina in a controlled manner and the stimulation of the light-sensitive ganglion cells was the same in all three conditions. This allowed scientists a way to separate the light properties that might affect the sleep-wake cycle.

Dr. Blume said they decided to focus on blue and yellow light in this study as a study in 2019Trusted Source on mice found that yellowish light had a stronger effect on the mice’s rest-activity cycle than blueish light.

“The most striking changes in brightness and light color (i.e., changes from orange to blueish or vice versa) occur around sunrise and sunset, marking the beginning and end of a day,” Dr. Blume noted.

“Thus, especially changes along the blue-yellow dimension may be relevant for the internal biological clock.”

Variation in light color does not affect circadian rhythm

At the conclusion of the study, researchers reported they found no evidence that the variation in light color along the blue-yellow dimension played a relevant role in affecting human circadian rhythm.

“Rather, our results support the findings of many other studies that the light-sensitive ganglion cells are most important for the human internal clock,” Dr. Blume said.

The researchers still recommend people reduce their exposure to short-wavelength light emitted from smartphones and other technology devices — despite what color it may be — before going to sleep, as they can affect circadian rhythm.

“The problem is that in everyday language we often refer to the short-wavelength light to which the specialized ganglion cells are most sensitive as ‘blue light’,” Dr. Blume explained. “This is despite the fact that the light does not have to be perceived as blue.”

“Our results support the findings of many other studies that the light-sensitive ganglion cells are most important for the human internal clock,” she continued.

“Therefore, short-wavelength light — misleadingly often termed ‘blue light’ — should be reduced in the evening, for example by dimming computer screens and using a night-shift mode. Avoiding screen time before bed can also help, as the things we do on our phones often delay sleep.”

Many factors affect the body’s ‘internal clock’

After reviewing this study, Dr. Benjamin Bert, an ophthalmologist at MemorialCare Orange Coast Medical Center in Fountain Valley, CA, told MNT that this study was interesting as it tried to show that while light color may not make a difference to a person’s sleep-wake cycle, other aspects that could.

“They talked about low melanopic lightTrusted Source, which still is trying to get rid of the short wavelength light, in order to allow for an easier time of going to sleep,” Dr. Bert continued.

“But I think what we’re really seeing is that it’s so multifactorial that trying to figure out one specific thing that could be contributing to these issues or these concerns needs a lot of research to flush it out.”

MNT also spoke with Dr. Alexander Solomon, a surgical neuro-ophthalmologist and strabismus surgeon at Pacific Neuroscience Institute at Providence Saint John’s Health Center in Santa Monica, CA, who said the modulation of a person’s internal circadian rhythm is rather complex.

“There is a master ‘clock’ set by melanopsin cellsTrusted Source — which are still most sensitive to blue light — but other activities such as meal timing and exercise can feed back to that master clock as well,” Dr. Solomon added.

Decreasing light exposure before bed may improve sleep

Dr. Solomon said if a person is having difficulty sleeping and waking at a regular time needed for their lifestyle, one change could be to use blue light-blocking glasses or a similar phone or screen setting, but also to decrease overall exposure to bright light.

“Quite frankly, as shown by this study, a bright enough yellow light or medium brightness normal lighting is equivalent to a dim blue light after a certain time,” Dr. Solomon explained.

“There can be many other factors that play a role in difficulty sleeping, and seeing a sleep specialist/hygienist may be helpful before attributing it to a single factor such as light exposure,” he added.

Dr. Bert agreed: “Usually when we’re looking at something, we’re also activating the brain, which makes it harder for us to kind of calm down and be able to easily go to sleep.”

“It would still be a good practice to take a break from anything that is projecting light into your eyes a few hours before trying to go to sleep and just give yourself some time to relax and let your brain calm down as well to ease you into sleep.”

— Dr. Benjamin Bert, ophthalmologist

Poorer sleep health associated with elevated CVD risk

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Poor sleep health was associated with increased risk for experiencing CVD, according to data published in Scientific Reports.

Researchers reported that for each component (regularity, satisfaction, alertness, efficiency, duration and sleep actigraphy) of a composite sleep health measure, participants experienced an incrementally larger risk for CVD compared with those with healthy sleep.

Heart clock

“Insufficient or poor sleep is a significant risk factor for heart disease. Studies have mostly used single sleep measures (often focusing only on sleep duration, quality or insomnia). However, a composite of multidimensional sleep health may be more predictive of heart disease than single sleep measures,” Soomi Lee, PhD, assistant professor in the College of Behavioral and Community Sciences at the University of South Florida School of Aging Studies, and colleagues wrote. “Our approach lends itself to characterizing a ‘sleep health’ message that will be more effective in motivating the public to engage in multiple sleep health behaviors that may have synergistic effects on decreasing the risk of heart disease.”

For this study, researchers utilized the data of 6,820 individuals (mean age, 53 years) from the Midlife in the U.S. study (MIDUS) to evaluate whether composite measures of sleep health were associated with CVD. Researchers assessed two sleep health composites: the first, based on self-report only, assessed regularity, satisfaction, alertness, efficiency and duration of sleep; the second was based on each of the previous self-reported variables plus sleep actigraphy.

The outcome of CVD was also self-reported (MI, angina, valvular disease, atrial septal defect, ventricular septal defect, CAD, CHD, ischemia, arrhythmia, heart murmur, HF and/or other). Hypertension was excluded as a sleep health-related CVD.

Sleep health and CVD risk

After full adjustment, researchers reported a significant association between self-reported sleep health and risk for heart disease, with each unit increase in measures of poor sleep health associated with a 54% greater risk for CVD (adjusted RR = 1.54; P < .001). For each unit increase in measures of poor sleep health from the second composite including actigraphy, researchers observed a 141% greater risk for CVD (aRR = 2.41; P < .001).

Lee and colleagues proceeded to conduct a sensitivity check using unweighted sleep health composites and reported generally consistent yet weaker findings, with a 14% greater risk for CVD with each additional dimension of poor sleep (aRR = 1.14; P < .001). The association between poor sleep health and CVD failed to meet statistical significance in the sensitivity check using the unweighted self-reported second composite plus actigraphy (aRR = 1.22; P = .073).

Subgroup analyses by sex and race

Lee and colleagues noted that women reported more sleep health problems based on the first composite but not the second composite that included actigraphy. Although men were more likely to report CVD compared with women, sex did not moderate the association between sleep health and risk for CVD.

Although Black individuals experienced the highest number of unhealthy sleep variables and the highest prevalence of CVD, researchers reported that sleep health and CVD risk were more strongly related in white participants compared with all other races in the self-reported second composite plus actigraphy (P = .001).

Moreover, the slope for the association between more sleep health problems and increased risk for CVD was similar between both Black and white participants (P = .151), but other races and ethnicities did not follow the same pattern.

“The current study shows the importance of considering ‘co-existing sleep health problems’ within an individual to assess the risk of heart disease,” the researchers wrote. “Findings revealed having more sleep health problems may increase the risk of heart disease in middle adulthood. Results were consistent between two independent samples using different sleep health composites (using self-report only and both actigraphy and self-report). Despite known differences in the prevalence of sleep and heart disease by sex and race, the association between sleep health and the risk of heart disease did not generally differ by sex and race in our study. The findings highlight the importance and utility of assessing multidimensional sleep health in predicting the risk of heart disease and potentially other health outcomes.”

Sleep Apnea Has Moved Past Darth Vader Masks

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People with sleep apnea need not suffer anymore. Long gone are the days of only one or two mask options and loud, noisy and bulky CPAP machines. You can find relief if you have been diagnosed with sleep apnea — or think you may have sleep apnea — but do not want to be strapped to a mask that reminds you of Darth Vader.man sleeping with sleep apnea mask

Sleep apnea is a potentially serious sleep disorder in which breathing repeatedly stops and starts. You may have sleep apnea if you snore loudly and you feel tired even after a full night’s sleep.

“I have been helping patients with sleep apnea for 20 years and have seen many changes in continuous positive airway pressure (CPAP) machines that deliver air pressure through a mask placed over your nose while you sleep,” says Kara Grottke, Mayo Clinic Health Systemrespiratory therapist. “The air pressure is somewhat greater than that of the surrounding air and is just enough to keep your upper airway passages open, preventing apnea and snoring.”

Older devices would take up most of your nightstand, and the machine would keep both you and your significant other awake at night. Or, if you were able to adjust to the noise coming from the machine, you were waking up every hour to readjust your mask because the fit just wasn’t made for the curves and uniqueness of your face.

The machines now are small enough they can be held in one hand and, when coupled with a good mask seal, are whisper-quiet when in use. Manufacturers have heard the consumer and agree that one or two sizes do not fit all. There also are many mask options, sizes and styles from which to choose:

  • Nasal-style masks are small, lightweight and fit over your nose.
  • Pillow-style masks fit just under your nostrils. These are quite small and feel like hardly anything is on your face.
  • Full face-style masks fit over your mouth and nose, but they are much more lightweight and look and feel very different from the big bulky masks from years ago.

“I understand that the thought of going to bed with something attached to your face and blowing air may seem undesirable,” adds Grottke. “However, I continually hear from patients that they didn’t realize how much they were missing out on before they used a CPAP machine. They knew they were tired, and that untreated sleep apnea had many health consequences, but they didn’t know how good they could feel.”

Using a CPAP machine can be frustrating at first, but it is important to stick with it. With time and patience, CPAP can positively affect your quality of life and health.