Why a short night costs more than you think
You will be able to: Name four ways a short night shows up the next day, and explain why you may not notice it yourself.
Sleep is often the part of the day we trim when work runs late. A short night rarely feels like a big deal. The research says it is.
1. Your attention and reactions slow down
The US National Heart, Lung, and Blood Institute (NHLBI) lists the everyday effects of too little sleep plainly: trouble learning, focusing and reacting.
The best-known way to picture the size of the effect comes from a study in Australia. Researchers kept 39 people, mostly transport workers, awake for up to 28 hours and tested them regularly. On a different occasion, the same people drank measured amounts of alcohol and did the same tests. After 17 to 19 hours without sleep, their results on some tests were as bad as or worse than at a blood alcohol concentration of 0.05%. After longer without sleep, they matched the highest dose given, 0.1%.
This is not a rare situation. In a US survey across 19 states, about 1 in 25 adults (4.2%) said they had fallen asleep at the wheel at least once in the previous 30 days. The warning signs the US Centers for Disease Control and Prevention (CDC) list are worth learning: frequent yawning or blinking, not remembering the last few miles, missing your exit, drifting out of your lane, and hitting the rumble strip. Opening a window or turning up the radio does not fix it. Stopping somewhere safe and resting does.
2. Your mood and your read of other people change
The NHLBI also notes that people who are short of sleep can find it harder to judge other people's emotions and reactions, and may feel frustrated, cranky or worried in social situations.
3. You may not notice how far you have slipped
This is the part that surprises most people. In a study at the University of Pennsylvania, healthy adults spent two weeks in a lab with either 4, 6 or 8 hours in bed per night. The 6-hour group's test results got worse night after night, and by the end the short-sleep groups' scores were as poor as after one or even two nights with no sleep at all (the 4-hour group fared worst). Yet their own rating of how sleepy they felt rose at first and then levelled off.
In plain words: after a few short nights, you get used to feeling a bit flat and start calling it normal, while your performance keeps sliding. Feeling fine is not proof that you are fine. This is why, in this course, we measure instead of guessing.
Try it: your 1-minute alertness test
Sleep researchers measure alertness with a simple reaction test: wait for a signal, respond as fast as you can, again and again. Here is a 1-minute version. Do one run now, then try it again first thing in the morning and late in the evening, or after a short night, and compare. The results are saved in this browser with the time of day.
4. Over months and years, your health keeps the score
The American Academy of Sleep Medicine and the Sleep Research Society reviewed the evidence together. Their joint statement says that regularly sleeping less than 7 hours is associated with weight gain and obesity, diabetes, high blood pressure, heart disease and stroke, depression and a higher risk of death, as well as weaker immune function, more pain, more errors and more accidents.
"Associated with" matters here: these studies show a link, not always a cause, and other factors play a part too. And one carefully controlled study points in the same direction.
In it, 164 healthy volunteers had their sleep tracked with wrist monitors for a week, and then were given a common cold virus in nasal drops under quarantine. Those who had slept 5 to 6 hours a night were about four times more likely (in odds) to develop a cold than those who had slept more than 7. Sleep was measured, not assigned, and the groups were small, so the exact size of the effect is uncertain.
What to take from this
You do not need to be perfect. You need to know your number and protect it most nights. The next article finds that number.
Quick check (3 questions)
Sources
- NHLBI, Sleep deprivation and deficiency
- Williamson & Feyer (2000), Occupational and Environmental Medicine 57(10): 649-55, PubMed 10984335
- GOV.UK, The drink drive limit
- CDC MMWR (2013), Drowsy driving, 19 states and DC, 2009-2010
- Van Dongen et al. (2003), Sleep 26(2): 117-26, PubMed 12683469
- Watson et al. (2015), AASM and SRS joint consensus statement, PubMed 26039963; AASM summary (PDF)
- Prather et al. (2015), Sleep 38(9): 1353-9, PubMed 26118561
- Basner & Dinges (2011), Sleep 34(5): 581-91, PubMed 21532951 (the reaction test)
Next: how much sleep do you need?