IMPORTANCE of SLEEP....for Health
How the Cycles of Light and Darkness Affect Your Health and Wellbeing
January 19, 2014 |
By Dr. Mercola
While it may not be immediately obvious as to why, light is actually crucial to your health. I've always believed that you could have the ideal lifestyle with respect to the food you're eating, the water you're drinking, and exercise, but if you don't sleep well, you're just not going to be optimally healthy.
Poor sleep inevitably leads to health problems. Maintaining a natural rhythm of exposure to daylight, and darkness at night, is an essential component of sleeping well.
Researcher Dan Pardi, who is employed by the Behavioral Sciences Department at Stanford University, also works with the departments of neurology and endocrinology at Leiden University in the Netherlands.
"I look at how sleep deprivation, or not getting enough sleep or the amount of sleep that you need, can influence decision making and cognitive processes like reaction time, memory, impulsivity, and how that relates to food choice," he explains.
He's also the CEO of a new start-up company called Dan's Plan, which seeks to help people optimize their health by maintaining good sleep habits.
How Much Sleep Do You Really Need?
Your sleep requirements change across your lifespan. Most infants will sleep a good percentage of the day. By adulthood, the amount of sleep typically settles somewhere around seven to nine hours. According to Pardi, the average, across a sample population, is about eight hours of sleep per night.
That said, sleep requirements are highly individual, and can change from one day to the next, depending on factors like stress, physical exertion, illness, pregnancy, and so on.
With so many variables, figuring out your optimal sleep requirement is a bit like a moving target. So, how can you tell you've achieved enough sleep? According to Pardi, the following three factors are part of the equation:
One of the easiest ways to gauge whether you've slept enough is to assess your level of sleepiness the next day. For example, if you had the opportunity, would you be able to take a nap? Do you need caffeine to keep you going? That said, research has shown that your own subjective rating of sleepiness is not always an ideal way to assess your sleep.
According to Pardi:
"The reason why is that after a few days of insufficient sleep or not getting enough sleep on a daily basis, the amount of sleepiness that you experience tends to saturate. It doesn't get much worse; it gets pretty bad over a few days, and then it actually levels out," he explains.
"If you were to measure objective measures of cognitive performance like reaction time, you would see that those would continue to get worse if you maintained an insufficient sleep pattern on a day-by-day basis. That's one of the big problems in our society today. It's that we basically accommodate feeling sleepy that that feeling starts to feel normal. But then we have continual impairment in how well our brain is performing.
Your mind requires proper sleep to be able to focus its attention on one particular task... That is one of the cardinal aspects of attention deficit disorder that can happen to both adults and children.
We're getting 20 percent less sleep on average as a population than we were in 1960s. That's equivalent to one whole night of sleep loss, which is also clinically meaningful, meaning, at that level of sleep loss we experience very significant issues."
How to Improve the Quality of Your Sleep
As mentioned earlier, the quality of your sleep has a lot to do with light, both outdoor and indoor lighting. The reason why light is important is because it serves as the major synchronizer of something called your master clock.
This master clock is a group of cells in your brain called the suprachiasmatic nucleus (SCN). As a group, these cells synchronize to the light-dark cycle of your environment. You also have other biological clocks throughout your body, and those clocks subsequently synchronize to your master clock.
"There are two levels of synchronizations taking place: the master clock with the environment and your body clocks with the master clock," Pardi explains. "So many different physiological factors will maintain a 24-hour pattern; whether that is eating behaviors, cell cycle, growth and repair process, or whether it's hormone patterns."
In the non-artificial light environment of our historical past, people basically experienced light according to when the sun rose and when it set. Now, with the advent of the light bulb, artificial light, high-definition televisions, and any number of lighted electronic gadgets, we're exposed to a lot more light over a 24-hour period, and a lot less complete darkness. This throws off all of your internal rhythms and clocks. There are significant consequences to this, including but not limited to:
Shift workers, for example, are known to have four- to five-folds higher rates of cancer than the average population. They also have higher rates of obesity and diabetes. But you don't have to be a classic shift worker to put yourself in this high-risk category. As explained by Pardi:
"There's a new type of shift work, where people go to work in the morning, they come home, they spend a little bit of time with their families, and then they go back to work on their computers... This is a pattern that a lot of people in the modern workplace maintain. Again, this new type of shift work is also throwing off our rhythms very significantly."
Exposure to Outdoor Light Is Critical for Maintaining Your Master Clock
Most people in Western societies spend the larger portion of each day indoors, which essentially puts you in a state of "light deficiency." In terms of light intensity, outdoor light is far more intense than indoor light. Light intensity is measured in lux units, and on any given day, the outdoor lux units will be around 100,000 at noon. Indoors, the typical average is somewhere between 100 to 2,000 lux units—basically two orders of magnitude less.
"We're not getting enough bright light exposure during the day, and then in the evening, we're getting too much artificial light exposure. Both of those have the consequence of causing our rhythms to get out of sync," Pardi says.
So, in terms of practical advice to help you maintain your master clock, you want to get bright light exposure during the day. Indoor light simply isn't intense enough to do the job. So-called "anchor light" anchors your rhythm, causing it to be less fragile, so that light at night has less of an ability to break your rhythm. As for how much light exposure you need, Pardi saysthe first 30-60 minutes of outdoor light exposure creates about 80 percent of the anchoring effect—a classic Pareto principle.
This is useful information indeed, as this means that even just going outside for half an hour at lunch time can provide you with the vast majority of anchoring light you need to maintain a healthy circadian rhythm. The ideal time to go outdoors is right around solar noon.
Exposure to Light Before Bedtime Hinders Sleep
Among other things, melatonin acts as a marker of your circadian phase or biological timing. In a nutshell, this hormone influences what time of day or night your body thinks it is, regardless of what time the clock on the wall displays. Somewhere between 50-1,000 lux is the activation range within which light will begin to suppress your melatonin production. Melatonin regulates your sleep cycle, and when it is suppressed, you may not feel sleepy enough to fall asleep. Insomnia can occur as a result.
One 2011 study1 compared daily melatonin profiles in individuals living in room light (200 lux) vs. dim light (3 lux). Results showed that, compared with dim light, exposure to room light before bedtime suppressed melatonin in 99 percent of individuals, and shortened melatonin duration by about 90 minutes. Furthermore, exposure to room light during the usual hours of sleep suppressed melatonin by more than 50 percent in 85 percent of trials. The authors concluded that:
"These findings indicate that room light exerts a profound suppressive effect on melatonin levels and shortens the body's internal representation of night duration. Hence, chronically exposing oneself to electrical lighting in the late evening disrupts melatonin signaling and could therefore potentially impact sleep, thermoregulation, blood pressure, and glucose homeostasis."
Simply closing your eyes is not enough, as even a tiny amount of light can penetrate your eyelids. You really need to make sure your bedroom is as pitch black as possible. I recommend installing blackout shades for this purpose. A far less expensive alternative is to use a sleep mask to avoid disrupting your melatonin production and circadian rhythm. Also keep in mind that digital alarm clocks with blue light displays will have a detrimental effect.
The Right Type of Indoor Lighting Can Counteract Effects of Evening Light Exposure
The four lighting factors that affect your circadian rhythm are:
When it comes to the wavelength of light, you want to make sure you're using the right tone of light in the evening. The ideal light tone for any light you keep on at night (including your alarm clock) is a reddish amber, certainly not blue or green. The red and amber will interfere least with your melatonin production. You also want to simply keep your lights as dim as possible, so investing in a dimmer switch may be a good idea.
You can also address this issue on your computer. Pardi recommends a free computer program called f.lux (see justgetflux.com2), which alters the color temperature of your computer screen as the day goes on, pulling out the blue wavelengths as it gets later. According to the site: the program "makes the color of your computer's display adapt to the time of day, warm at night and like sunlight during the day." There are also blue light-blocking glasses and special blue light-blocking bulbs you can buy. Pardi explains why blocking blue light works:
"Most of your listeners have probably heard of rods and cones in the eye. These are specialized cells that can transduce a photo signal into a nerve signal. But with those cells, that will go back to the primary visual cortex where we can turn light into images that we can understand and see.
A different type of cell in the mid-90s was discovered... [called] intrinsically photosensitive Retinal Ganglion Cell (ipRGC). It does the same thing. It actually will transduce light. But instead of going to your visual cortex, it goes to your master clock. Those cells are most responsive to blue light. If you can block blue light, you can actually create something called circadian darkness or virtual darkness. What that means is that you can see, but your brain doesn't think that it's daytime; your brain thinks that it's dark out. That is actually a practical solution for living with artificial light in our modern world... With more awareness, future digital devices will have red light [instead of blue]. Red or amber-toned light is much, much better."
Other Lifestyle Variables That Affect Your Circadian Rhythm
Besides exposing yourself to intense outdoor light during the day for a minimum of 30 minutes to an hour, there are other variables that can synergistically interact with your internal rhythms. Physical activity will affect your circadian clock, as will food consumption.
"For example, eating late at night is something that can decouple something called food-entrainable oscillator (FEO) from your master clock. Basically, your feeding patterns are in a rhythm that is orchestrated by the master clock. But you can decouple those rhythms by eating at a time that you usually don't eat – eating late at night," Pardi says.
He agrees that intermittent fasting is very promising in terms of its beneficial health effects. However, he stresses the importance of not eating too late. Ideally, you want to avoid eating at least three hours prior to bedtime. What you eat in the evening can also be a factor that keeps you from falling into restful sleep.
"There are different strategies about when to fast. Not eating breakfast is one. The risk to that is that you then have more hunger late at night. That can be problematic actually. You could completely negate the positive effects by eating too late. Another strategy is to just eat during daylight hours. You would eat in the morning, but you just wouldn't eat after darkness. I know of some people who are experimenting with intermittent fasting have benefitted. If you do skip breakfast, I would also put to have a rule where you don't eat within three hours of bed."
For Optimal Health, Keep Your Master Clock Timed Right
In short, if you want to get good sleep, you have to have properly aligned circadian rhythms. If you don't, the varying aspects of your waking/sleeping system will be working at the wrong time. Insomnia is a common side effect of an improperly timed circadian clock. You'll also end up being sleepy during the day. Worse yet, it can have a significantly detrimental effect on your brain function and ability to perform at school and work.
So first and foremost, you want to maintain natural and proper light rhythms. This includes exposing yourself to intense daylight, ideally around solar noon, for at least half an hour or more each day. A gadget that can be helpful in instances when you, for some reason, cannot get outside during the day is a blue-light emitter. Philips makes one called goLITE BLU. (You can find it on Amazon3 for less than $150.) It's a small light therapy device you can keep on your desk. Use it twice a day for about 15 minutes to help you anchor your circadian rhythm if going outdoors is out of the question.
Then, in the evening, you want to avoid the blue light wavelength. This can be done by using blue-blocking light bulbs, dimming your lights, and if using a computer, installing a blue light-blocking software like f.lux.4 Last but certainly not least, when it's time to go to sleep, make sure your bedroom is as pitch black as possible. For even more guidelines to help you get a good night's sleep, please see this previous article.