Month: May 2021

Recently, my brother mentioned he was sleeping better since he got new prescription glasses with a blue-light filter. He wears his glasses mostly for reading screens (both computer and smartphone) during the day while at work. So I was intrigued, but a little skeptical: could daytime use of blue light-filtering glasses make a difference in how well he slept? How, when, and why blue light affects us seemed like good questions to pose to an expert before deciding whether those glasses could help me, too.

What is blue light?

Visible light includes a short segment of wavelengths tucked into the electromagnetic radiation spectrum. Together, the wavelengths of visible light captured by our eyes are translated into white light by our brains.

You may remember looking through a prism to bend the wavelengths that make up white light into a rainbow of colors. At one end of this rainbow, blue light shades toward violet. Sunlight has a lot of light at all visible wavelengths.

Measured in nanometers (nm), visible light wavelengths range from 400 to 700 nm. Blue-light wavelengths lie between about 450 and 495 nm. And different slices of blue-light wavelengths have different effects on our bodies, including on sleep and alertness.

How does light affect our bodies?

In addition to helping us see, light also has nonvisual effects on the body, says Dr. Steven Lockley, a neuroscientist at the Division of Sleep and Circadian Disorders at Harvard-affiliated Brigham and Women’s Hospital.

The 24-hour circadian clock in the brain regulates sleep and wake cycles, hormonal activity, eating and digesting, and other important processes within the body. “Special photoreceptors in the eye detect light to control our circadian rhythms,” he says. These cells contain a nonvisual photopigment called melanopsin, which is most sensitive to 480 nm light at the blue-green end of the visible light spectrum. Other visual photoreceptors called cones allow us to see even shorter wavelengths of blue-violet light at around 450 nm.

How can blue light affect sleep?

During the day blue-enriched light is desirable, because it helps synchronize our circadian clocks to a 24-hour day. So, exposure to a regular light-and-dark cycle is vital to achieve and maintain good sleep.

Stimulation from certain wavelengths of blue light helps us stay alert, whether this comes from a natural source like the sun in daytime hours, or from electronic devices that emit blue light. While the stimulation is helpful during the day, at night it can interfere with sleep. Blue-light exposure in the evening — for example, binging a TV series on your laptop right before bed — will stimulate the melanopsin-containing cells and alert the brain, making it think it is daytime. That can make it harder to fall asleep and may affect the quality of your sleep.

Blue-light filtering: Can it help a tired body and tired eyes?

Although a recent systematic review suggested that blue light-blocking glasses may help people with insomnia, Dr. Lockley says there’s not enough detail about the studies to draw that conclusion. Most commercially available blue light-filtering glasses, and special coatings added to prescription lenses, aren’t standardized. So you have no way of knowing which wavelengths are being blocked, and whether this affects only visual function, or important nonvisual functions such as alertness and the circadian clock. Also, the timing, duration, and nature of the nighttime light exposure in the summary of these studies was not clear.

If you want to block stimulating blue light that could interfere with sleep, avoid screen use as much as possible after dusk — especially within two to three hours of bedtime. You can also try using computer software that reduces the amount of blue light emitted. Examples include Night Shift (available on Apple devices) or f.lux, a free download available for all computers and related devices. You should also try to address other issues that affect your sleep.

To help reduce eye strain, a common concern for people who use screens often, the American Academy of Ophthalmology advises taking regular breaks using the 20-20-20 rule. Every 20 minutes, look away from your screen at an object about 20 feet away for about 20 seconds.

You should also get as much daylight exposure as possible in between screen use to provide a strong circadian and alerting stimulus, particularly if you spend most of your time indoors.

As for my brother, he doesn’t watch much television and tends to prefer reading print books in the evenings. He agreed that he might be experiencing a placebo effect from the blue-light filter on his new glasses — or simply that he is sleeping better now that he has the correct prescription, and therefore less eye strain.

As the holiday season approaches, there’s a lot to keep in mind. Let’s just start with the easy questions: Who’s hosting Thanksgiving? Who’s making the turkey? The stuffing? Dessert?

But as we embark on our second round of holidays during the COVID-19 pandemic, we all have additional questions and decisions to make about how to keep everyone safe:

• Inside or outside? While outside is safer, it may be too cold where you are to consider dining outdoors.
• Is it necessary to wear masks or keep a physical distance? That depends on everyone’s vaccination status, recent exposures, and risk tolerance.
• Must everyone be vaccinated? For many, this one’s a dealbreaker. Some hosts may insist. And some family and friends may come only if everyone is vaccinated.

The role of COVID testing could be changing

We know a lot more about testing for COVID-19 than at this time last year:

• PCR tests. This is still the most accurate test of current infection. It detects small amounts of genetic material from the virus that causes COVID-19. But it often takes days to get the result back.
• Rapid tests. This is typically an antigen test. It detects small bits of viral protein using similar technology to that used in pregnancy tests. An advantage of this type of testing is that the results are back in minutes. And while these tests have a higher rate of false negatives than a PCR test, getting a negative result strongly suggests you aren’t contagious. Even if you are infected, a negative result suggests there’s too little virus to infect others, at least at the time of the test. So, rapid COVID tests could be used as a way to screen people just before an activity during which exposure is possible — like Thanksgiving or other holiday gatherings.

One approach is to offer testing for each person as they arrive. It might slow the reunion process down a bit, but only for a few minutes. If a visiting friend or family member tests positive, they should leave along with anyone else they might have already exposed. The next step for them would to be to quarantine while waiting for results from a PCR test.

Cost, availability, and other limits of rapid testing before gatherings

While rapid testing may be a useful way to reduce your risk as holiday gatherings approach, it’s not perfect. Cost per test is high, generally $10 to $40 in the US. That’s especially hard for people with limited resources and those at higher risk for infection and complications from COVID-19. Rapid tests may be hard to find, too, although the Biden administration has vowed to address lack of availability by pledging several billion dollars to expand rapid testing. The health department in your community may be able to help you find test sites.

The FDA has given emergency use authorization to nearly 40 different tests, and research suggests that different brands vary widely in their accuracy. Currently, there are no specific recommendations from experts about which rapid test is best.

Additionally:

• Results only apply to the time that the test is performed. You could have a negative test today despite being infected and a positive test tomorrow. These false-negative results may occur because it’s so early in the infection that there isn’t much viral protein present. Or it could be because of how the sample was obtained — maybe the swab wasn’t inserted deeply enough into the nose or wasn’t twirled around for long enough. Repeated testing can be helpful to address the concern of false-negative results; in fact, some tests specifically recommend repeat testing within a few days.
• False-positive results may occur. A test may indicate infection when no such infection is present. It’s what happened on a now-infamous episode of The View. Two hosts quickly exited the set during a live broadcast because their COVID tests were positive. Soon after, their results were declared incorrect after further testing was done. Although false-positive results should be quite rare, manufacturing problems may make them more likely. In fact, some tests have been recalled because of an unexpectedly high rate of false-positive results.
• Be prepared to download an app and follow instructions carefully. Rapid tests for COVID-19 typically require you to download an app and connect your phone or computer to the testing device through the app. Then you need to use a swab to collect a sample from inside your nose, apply the swab to the chemicals from the kit, and wait 15 minutes or so for your device to tell you the result. It’s not a particularly intuitive or consumer-friendly process. Many people may find it challenging.

The bottom line

Despite its limitations, rapid testing for COVID-19 is a strategy worth considering for holiday gatherings or group activities during which exposure to the virus is possible. Ideally, simplified rapid testing will become readily available at low (or no) cost soon. So, think about putting rapid COVID testing on your holiday to-do list, and consider offering tests to guests before you sit down for the turkey. It doesn’t take long, and the turkey probably won’t be ready on time anyway.