Better Sleep Starts with Better Light

How Light Affects Your Sleep

Light plays a major role in how your body knows when to wake up, when to feel alert, and when to prepare for sleep. This process is largely guided by the suprachiasmatic nucleus, or SCN, which acts as the body’s master clock.

The light-detecting cells in our eyes notify the SCN when there is light outside. These cells are especially good at detecting blue light, which is naturally found in sunlight. This is helpful in the morning because it tells the body that the day has begun. The problem is that blue light in the evening can send the body the wrong message.

When the body is preparing for sleep, exposure to blue light can make it harder for the brain to recognize that night has arrived. In practical terms, this means the timing, amount, and source of light we are exposed to can influence how well we sleep.

Sleep experts commonly point to four important strategies.

Get Sunlight First Thing in the Morning

Being exposed to sunlight first thing in the morning sends your SCN a simple message: good morning.

After spending the previous few hours in darkness, your system is more sensitive to light in the morning. That means even a relatively small amount of morning light can be effective in helping your body recognize that the day has started.

This does not mean looking directly at the sun. You should never stare at the sun because it can permanently damage your retina. The goal is simply to get natural outdoor light into your eyes safely.

Spend Time Outside During the Day

Spending time outside during the daytime helps as well, even when it is cloudy. Outdoor light is still much brighter than indoor light, which is one reason daylight exposure can be so useful for supporting the body’s internal rhythm.¹

Being outside helps make the master clock more robust. It also helps synchronize that central clock with the outside day and with the peripheral clocks throughout the body.

In other words, light exposure is not only about waking up in the morning. The light you get throughout the day helps reinforce your body’s internal rhythm.

Be Mindful of Screens at Night

Blue light-emitting screens can interfere with sleep, especially when they are used close to bedtime. Some experts recommend avoiding screens at least an hour before your usual bedtime.¹

The effect may depend on the type of screen and how close it is to your face. A television across the room does not appear to be as disruptive as a phone, tablet, or computer screen held close to the eyes. The amount of natural light you get during the day may also matter. If you were exposed to a lot of outdoor light earlier in the day, you may be less affected by screen light at night.¹

Children are more sensitive to light, which means they may be more affected by evening screen exposure. A 2024 National Sleep Foundation consensus statement found that screen use can impact sleep health across the lifespan, with special concern for children and adolescents.²

Sleep in a Cool, Dark Room

Many experts agree that a good sleep environment should be cool and completely dark. If you wake up in the middle of the night, it is best to avoid turning on bright lights, especially devices that emit blue light, such as a phone or tablet.

The evidence for this recommendation is strongest in children, though the body of evidence continues to evolve for other age groups. As sleep researcher Erin Flynn-Evans explained, “The influence of light never ceases to amaze me in that every year it seems we learn something new about how powerful light is and how [even] little light exposure is impactful.”¹

The Bottom Line

Your body is constantly paying attention to light. Morning sunlight helps tell your brain the day has started. Daytime outdoor light helps strengthen your internal clock. Evening blue light can confuse that system, especially when it comes from screens close to your face. A cool, dark room helps protect the sleep environment your body needs.

Better sleep does not always begin at night. Often, it begins with the light you get first thing in the morning and the light you choose to limit before bed.

References

1. “Screen Time and Sleep: It’s Different for Adults,” Restorative Sleep, Stanford Lifestyle Medicine, August 8, 2024. https://longevity.stanford.edu/lifestyle/2024/08/08/screen-time-and-sleep-its-different-for-adults/

2. Lauren E. Hartstein et al., “The Impact of Screen Use on Sleep Health across the Lifespan: A National Sleep Foundation Consensus Statement,” Sleep Health 10, no. 4, August 2024, 373–384. https://doi.org/10.1016/j.sleh.2024.05.001

More sleep can double your testosterone

More sleep can double your testosterone level

Older men can sometimes double their testosterone levels by getting more sleep, according to a human study that Plamen Penev of the University of Chicago published in Sleep.

Not enough sleep
Nearly all of us probably get too little sleep, mainly because we are seduced every day by the technology around us. It enables us to generate light at night, provides us with 24-hour entertainment and information through electronic media, and makes it possible for us to have contact with each other whenever we want. Every evening, when our body tells us that it's time to sleep, we can also do a thousand other things instead.

Sleep & hormones
Too little sleep messes up our hormone balance. It makes our body less sensitive to insulin for example. Dutch researchers recently showed that after just one night of four hours' sleep, young men's insulin sensitivity went down by twenty percent [J Clin Endocrinol Metab. 2010 Jun;95(6):2963-8.] and that of diabetics by a quarter. [Diabetes Care. 2010 Jul;33(7):1573-7.]

In the latter case, lack of sleep is clinically relevant, so doctors could advise diabetics who react insufficiently to their medicines to get more sleep. "Sleep duration might become another therapeutic target to improve glucoregulation in type 1 diabetes", the Dutch researchers say.

Sleep & testosterone
Testosterone is also affected by amount of sleep. That's not so strange, as our bodies make much more testosterone when they're asleep than when they're awake. [J Clin Endocrinol Metab. 2005 Aug;90(8):4530-5.] The figure below is from the study mentioned here. It shows how much testosterone is present in the blood of 22-32 year-old men while asleep and during the rest of the day.

The better men sleep, the higher their testosterone level rises while they are asleep. [J Clin Endocrinol Metab. 2001 Mar;86(3):1134-9.]

In the average male over forty, the testosterone level goes down by 1-2 percent per year, but researchers occasionally come across men in their eighties with a testosterone level you'd expect in a young man. Add to that the fact that many older men – but not all men – sleep less and less deeply as they get older, then you automatically think of the idea that Plamen Penev wanted to test in his study: does the testosterone level decrease in older men because they sleep less?

Penev based his theory on, among other things, research done by Eve Van Cauter, a sleep researcher at the University of Chicago who has celebrity status in the field of endocrinology. Van Cauter discovered early in the 21st century that men in their forties make less testosterone while sleeping than men in their twenties.[J Clin Endocrinol Metab. 2003 Jul;88(7):3160-6.]

Study
Penev measured the amount of testosterone 12 slim, healthy, non-smoking men aged between 64 and 74 had in their blood in the morning. He also got the men to wear a small gadget around their wrist, which enabled him to see how many hours per night the men slept. That varied from 4.5 to 7.5 per 24 hours. The longer the men slept, the figures below show, the more testosterone there was circulating in their blood.

The men that slept the least had a testosterone level of 200-300 ng/dl. That's a normal amount for men of this age, but it's on the low side. The men in the study who slept the most had a testosterone level that was twice as high: 500-700 ng/dl. That's a level you'd expect in healthy young men.

Conclusion
"These findings suggest that complaints of poor or insufficient sleep in otherwise healthy older men can be associated with a more pronounced age-related androgen decline", writes Penev. "Eliciting such sleep complaints in the physician's office may facilitate the judicious interpretation of lower testosterone levels in the older male patient."

Before men consider doing testosterone therapy, they might first measure the amount of sleep they get. And 'measuring' is different from 'guessing' or 'estimating'. Most people overestimate the number of hours that they sleep. This was also the case in Penev's study. The men thought that they slept seven and a quarter hours per day on average, but Penev's recordings showed that they only slept six hours a day.

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Reference: Sleep. 2007 Apr;30(4):427-32.

4 Reasons Why You Need Quality Sleep

1. Want leaner legs? - Phase 1 & Phase 2 detoxification happen during sleep, if your sleep is poor you will have higher body fat on the lower body. Also, it will be more difficult to lower stored body fat on Thighs, Hamstrings, Knee, Calves

2. Sleep deprivation can increase inflammation, which will lead to a reduction in insulin sensitivity. Which will lead to a increase in body fat over time due to insulin resistance.

3. Sleeping just one less hour can lead to a increase of hunger as much as 45% according to one study on sleep & nutrition habits.

4. Sleep is a opportunity for the body to repair itself. Most restorative functions of the body happen overnight, so poor sleep will comprise your ability to recover from your training sessions.