Sleep and its Health Implications

Answers by Spencer Dawson, PhD, a sleep scientist, clinician and postdoctoral fellow in the Northwestern University Feinberg School of Medicine Department of Neurology.

Sleep need varies from person to person, similar to calorie needs. Recent recommendations are that adults obtain 7 to 9 hours of sleep per night. Obtaining fewer than 7 hours per night is associated with increased risk of a number of health consequences, as is sleeping more than 9 hours per night.

Yes, they do. The CDC recommends that school age children get 9-12 hours of sleep per 24 hours, and that teens get 8-10 hours. The brains of children and adolescents are still developing. Sleep is a critical time during which this development occurs.

Sleep quality may differ from night to night, even if sleep quantity remains the same. Timing of sleep, alcohol, caffeine, certain medications and outside disturbances can all worsen sleep.

In addition, it is important to make the distinction between sleepiness and fatigue. Sleepiness is directly related to our physiological need for sleep. The longer we have been awake, the sleepier we become. The longer we sleep, the less sleepy we become. Fatigue, on the other hand, is more closely related to energy levels and is determined by a number of different factors. These fatigue-inducing factors can include activity, diet, appetite, blood sugar, mood, illness, medications and other substances.

Timing is very important for sleep quality. Proof of this can be readily found by trying to work a night shift and sleep during the day, or traveling across several time zones. Our biological clock controls biological and behavioral processes that naturally cycle throughout the day (circadian rhythms), including aspects of our metabolism, keeping them synced up with the local light-dark cycle. Because our master biological clock is working really hard to keep us awake during the day and asleep at night, going to bed too early can mean you have a hard time falling asleep, and going to bed too late can mean you wake up too early.

What’s most important is consistency – this allows your master biological clock, circadian rhythm and sleep timing to be aligned for the best quality sleep. However, the most important thing to be consistent about is wake time. Bright light in the morning right after you wake up is what resets your biological clock and circadian rhythms. Changing your bedtime does not affect your biological clock as much, especially if you avoid bright light in the evening.

This does seem to be possible, to an extent. Because sleep is involved in so many biological processes, experts are quite divided on how to answer this question. It’s like asking whether you can catch up on exercise or healthy eating on the weekend – it can be a step in the right direction, but it’s not as good as consistently getting good quality sleep.

The big risk associated with catching up on sleep on the weekends is sleeping in after a late night, or just because you’re trying to catch up on sleep. Since your wake time (and bright light exposure when you wake up) tells your body what time it is and resets your biological clock, sleeping in for three extra hours is like traveling from New York to Los Angeles for the weekend. Come Sunday night, you may have a hard time falling asleep at bedtime, and you’re very likely to have a very hard time waking up Monday morning. Your brain will think it’s the middle of the night, and make it very hard to get up. This problem is so significant and so pervasive that it has its own name: social jetlag, because of how social activities push us into a different time zone without even traveling.

Learn more: Why a Slumber Party is the Best Way to Party This Year

The best indicator of whether you’ve had high quality sleep is how well you feel during the day, starting at least 30 minutes after you wake up. This short delay is important because the first 30 minutes can be influenced by sleep inertia. The initial grogginess that comes after waking from sleep may depend more on how deep your sleep was during the last few minutes before you woke up rather than the depth of your sleep for whole night.

If you are getting low quality sleep, your brain may decide to take more sleep during the day. If you find yourself dozing off during the daytime, then your nighttime sleep is almost certainly of low quality. Sleep is how your brain recovers from one day and prepares you for the next. So if you are able to accomplish your waking goals without excessive reliance on caffeine or feeling like you really need to force yourself, then you are almost certainly getting high quality sleep.

Unfortunately, the data available is fairly limited. Manufacturers create new devices much more quickly than independent researchers can test them and manufacturers generally do not share their own data. When calibrating these devices, the manufacturers are most likely testing them on relatively young and healthy individuals. This means that if you are older, younger, sicker or fitter than the test population, the device may not be as accurate for you.

In general, the accuracy of sleep trackers is probably increasing. Older and simpler devices measure wrist movement to infer whether you are asleep, which is not terrible but is certainly imperfect. One factor that likely contributes to increases in accuracy is the use of heart rate monitors. Besides measuring how fast your heart is beating, these devices can also measure the subtle changes in heart rate from beat to beat that are driven by the parasympathetic nervous system. The influence of the parasympathetic nervous system on heart rate increases when you fall asleep and increases even more during deep sleep.

Your sleep and circadian rhythms influence one another. The biggest influence on your master biological clock, which helps sync the circadian rhythms of your organs and tissues (such as when your body is focused on burning sugars versus burning fats), is from exposing your eyes to bright light, especially sunlight. Being asleep means you’re not getting exposure to light in the same way.

Every organ system in your body is influenced by sleep, so really the entirety of human health relies on good quality sleep.

One of the most important things for shift workers is called “anchor sleep”. This means trying to anchor your sleep schedule by having your sleep period on work nights overlap as much as possible with your sleep period on days off. The more consistency the better.

Since shift workers are typically working when the sun is not up – starting before sunrise or working long past sunset, their exposure to the bright light that tells the biological clock what time it is can be quite disrupted. The best fixes are to get bright light exposure – from a special light box or the sun itself – for a good period of time after waking, and to block as much light as possible before bed and certainly from the bedroom.

Avoid bright light before bed – turn the lights down to let your brain know it’s not daytime anymore. Keep your bedroom dark, quiet and cool. Your body temperature drops during sleep, so if you have too many blankets on, you’ll wake in a sweat.

If you can’t help worrying and planning for the next day when you’re trying to sleep, start setting aside a few minutes one or two hours before bedtime. Use this time to write down the things that are on your mind so that you can put them “on hold” until tomorrow. You don’t need much detail – just enough so that you can remember. If you like, add a note to yourself about what the next step is, or some different options if you’re trying to make a decision. Your brain does not work so great late at night, so you’re not likely to be as productive as during the day. Instead, allow yourself time to sleep so that you can return to the problems tomorrow when you’re refreshed.

Answer by Margarida Martins Oliveira, Ph.D., Registered Dietitian and member of the Portuguese Council of Nutritionists.

The brain has a master biological clock (in the hypothalamic suprachiasmatic nucleus) that modulates metabolism and gene expression in a time-of-day-specific manner, with daily oscillations of thousands of gene products.

Feeding also has a profound effect on the repertoire, phase and amplitude of rhythmic gene expression. More specifically, feeding-fasting cycles appear to function as potent Zeitgeber (timing cues) for peripheral clocks in the heart, liver, kidney, pancreas, etc., even bypassing the signals emitted by the master clock in the brain. For example, hepatic (liver) circadian rhythmicity is highly responsive to cyclic energy intake. In other words, the expression of hundreds of genes in the liver is influenced by food availability and time of feeding. Overall, the synchronization of peripheral clocks with our master biological clock is essential to ensure temporally coordinated physiology and metabolism. Peripheral clocks that are out of tune with one another and our master biological clock can create health issues.

Time restricted feeding (TRF) has some benefits to preserve circadian rhythms or these peripheral clocks. For instance, in healthy adults, reducing daily eating duration to 10 to 11 hours out of the day resulted in weight loss and improved sleep. In addition, the timing of food intake throughout the day is an important determinant of body weight. For instance, earlier meal times tend to be healthier and “better aligned” with our internal biological clock. In healthy people, higher energy intake at lunch is associated with a lower risk of weight gain. At night, eating during a time normally reserved for sleeping can result in weight gain. In fact, eating late influences the success of weight-loss therapy in obesity. Because energy expenditure is lower at night, it is advised to avoid consuming high-energy dense foods later in the evening and limit night-time snacking close to sleeping time.


Answer by Margarida Martins Oliveira, Ph.D., Registered Dietitian and member of the Portuguese Council of Nutritionists).

Sleep is important for neurological processing and physiologic restoration. Lifestyle factors such as caffeine consumption, alcohol intake and having high fat meals before nighttime sleep can contribute to poor sleep conditions. These behaviors are believed to disrupt circadian rhythms.

For a good nighttime sleep, you should reduce your caffeine intake slowly and limit your intake to one or two beverages daily (or 200mg of caffeine per day, early in the day). Even a small amount of caffeine consumed regularly is correlated with disruption in sleep duration, onset and perceived quality. Be aware that some foods and medications contain caffeine, including green tea, thus you should prefer naturally caffeine-free herbal tea.

Alcohol consumption prior to sleep leads to decreased sleep-onset latency early in the night (it may make you get to sleep more quickly) when blood alcohol levels are high, but induces subsequent disrupted, poor-quality sleep later in the night. To maximize your sleep quality, limit yourself to one or fewer alcoholic drinks at night.

Moreover, during sleep there is slower gastric motility (i.e. digestive activity). Because fat takes longer to digest along the gastrointestinal tract, you should limit high fat meals to at least two hours before nighttime sleep to avoid postprandial discomfort and disrupted sleep.

More references:

Exercise is a great way to improve your sleep. The best time to exercise is according to your  chronotype – are you a morning person or night owl? Try to exercise when you’re at your peak for best performance. Be sure to give your body at least 2 to 3 hours to cool down between the end of your exercise and when you go to bed.

Caffeine is probably the most commonly used substance with negative effects on sleep. Even if you think you sleep fine after an evening cup of coffee, the quality of your sleep may be reduced. Caffeine has a long half life: approximately 5 to 6 hours, which means half of the caffeine in a cup of coffee you had at at 6 pm will still be in your body at midnight.

Yes, but not much. Many of the ingredients in herbal teas can be relaxing. A pre-bedtime wind down routine can also help your brain and body get into a more relaxed state before trying to sleep. Herbal tea is a great addition to a this sort of routine. The only exception would be for people who are bothered by frequent urination during the night.

Supplements are likely to be most helpful for people who have deficits that can be corrected by those supplements. One of the most common sleep supplements in the U.S. is melatonin. This is a hormone that is related to sleep timing. So if you travel from California to New York, taking melatonin before bed can help your brain change the timing of sleep to be earlier, counteracting the effects of jetlag that would otherwise keep you up late and make it difficult to get up in the morning. It can also help people who work rotating shifts for the same reason. It will usually not do much to help people who are not having issues with the timing of their sleep. Most over the counter doses of melatonin are much larger than your body normally produces, so if you use melatonin, stick to a small dose, such as 0.3 to 2.0 mg.

It depends on the reason that your sleep is low quality, but usually the answer will be no. The main exception would be if the reason your sleep is poor is because of something external – like noise, light or the effect of a substance that disrupted your sleep on one or just a few nights.

More help than sleeping longer may be needed if your poor sleep lasts for weeks or months and especially if it is due to breathing problems or difficulty falling or staying asleep asleep. One problem with sleeping in is that it can shift your circadian rhythms later – like traveling several time zones to the West. This can make it more difficult to go to sleep and wake up when you want (or need!) to.

This depends on the reason your sleep quantity or quality is low. If you did not have an adequate opportunity for sleep last night, taking a nap today is a good idea. For example, if you have to stay up late or wake up early such that you only have 4 hours of sleep opportunity, taking a nap will help you regain some alertness the next day.

If you had an adequate opportunity for sleep last night (say 8 hours during the night in a comfortable environment) but only slept 5 hours, then a nap may lead to more sleep problems tonight. The most common reasons for poor quality sleep, apart from external causes, usually apply to naps as well, and so naps are not likely to be refreshing.

The majority of adults will do best when they are able to get 7 to 9 hours of sleep per night. A small minority of people need less, or perhaps are not actually able to sleep for 7 to 9 hours. There are many ways we compensate for inadequate sleep, including staying active, consuming caffeine and getting used to being in a state of sleep deprivation (as in not being subjectively bothered even if it is taking a toll on you),

It’s never a good idea to compare your own life, whose challenges you know intimately, to someone else’s “highlight reel”. They may have challenges you are unaware of, or they may be one of those rare people whose bodies and brains simply do not require as much sleep. This is like people who can maintain a healthy weight without particular attention to diet and exercise.

Sleep Disorders

Answers by Spencer Dawson, PhD.

The most common sleep disorders are insomnia and obstructive sleep apnea. If you suspect that you have a sleep disorder, consult your primary care physician or a board certified sleep specialist.

This is a question that a lot of people with insomnia have. The truth is that sleep need does vary between people, much like caloric need varies between people. Many people with insomnia think they need much more sleep than they are getting. What people with insomnia often find after they complete a Cognitive Behavioral Treatment for Insomnia (CBT-I, a non-medication approach, now regarded as the first line or gold standard treatment for adults with chronic insomnia) is that they feel quite well and able to get by with less sleep than they thought.

Getting your sleep back on track after a period of chronic insomnia can be different for every individual. In general though, if you are spending a lot of time in bed tossing and turning, taking over 30 minutes to fall asleep or being awake over 30 minutes during the night, you are probably trying to get more sleep than your brain and body need.

The most important thing to do is to get a sleep study to find out how serious the problem is. The bare minimum to be diagnosed with sleep apnea is that you are choking (literally – your airway collapses partly or completely) for 10 seconds every 12 minutes that you are asleep. Those episodes of choking can last much longer and can happen much more frequently. Then, it’s a good idea to discuss treatment options with an open mind. The gold standard treatment is called Continuous Positive Airway Pressure (CPAP). This device uses pressurized air to act as a splint to hold your airway open so that it does not collapse. There have been many great advances in CPAP technology, including many options of soft, flexible and comfortable masks, the ability to heat and humidify the air so that it’s just right, and options to automatically decrease the pressure to make it easier to breathe out. Still, for a variety of reasons, CPAP is not the best choice for some people, and there are other options available.

For people with mild to moderate sleep apnea, oral appliances, usually created by a dentist, reposition your lower jaw, thus opening  your airway wider to prevent collapse. For people whose sleep apnea is only a problem when they sleep on their back, positioning systems can help them stay off of their back, typically by holding something relatively uncomfortable, like a tennis ball, on their back. This way, if they roll over on their back during sleep, it will be uncomfortable and they will roll over without having to think about it.

If you’re sleeping more than 9 hours per night, and you are an adult, this may be a signal that something is wrong.

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