If you are an executive or owner of a business, you can probably count yourself amongst those who routinely run on minimal amounts of sleep – four to five hours a night is not uncommon. Margaret Thatcher was famous for only getting four hours of sleep a night during her years as a prime minister. But while many high-performing people cite this as a normal pattern of behavior for themselves, this flies in the face of the accumulated knowledge that states that adult humans need between 7-9 hours of sleep. What gives?

It’s tempting to think that the high level of success these people have achieved serves as proof that sleep isn’t so necessary for normal biological functions. It’s also important to note that these high-achieving people represent a small segment of society – just a few percent of all workers. Perhaps they’re so driven that they are able to overcome the effects of sleep deprivation. Perhaps they possess a rare genetic mutation that allows their body to function on less sleep. Perhaps they’re trying to pretend that they aren’t being affected, or maybe are too proud to admit that they are tired all the time. Regardless of what the reality is, you need your sleep.

A lack of sleep doesn’t just result in your feeling tired; your entire body pays a price when it isn’t well rested. Some of the worst effects from long-term sleep deprivation include:

Being unable to focus

If you are a college student who is burning the midnight oil, you probably know this all too well. Instead of being able to focus on the professor’s lectures, you instead find yourself barely able to keep your eyes open, let alone pay attention to what he/she is saying. At work, you’ll be subject to similar problems. Instead of being able to focus on what your boss is saying, you’ll instead focus on trying to keep your eyelids open. Your boss might even think that you aren’t even trying to pay attention to them, which is an even worse outcome. Focusing on reading documents becomes a chore, and remembering what it was that you were doing becomes increasingly difficult.

Putting on excess weight

Your metabolism is partially regulated by your sleep schedule. When you don’t get enough sleep, your body loses much of its ability to regulate your sense of hunger and fullness. As if that wasn’t bad enough, you also burn  fewer calories overall while awake. Both of these factors are exacerbated even further by the fact that you are awake for several more hours, and thus will need to eat more to stay full over that longer period of wakefulness.

An increased chance of burning out

Burnout can result from a number of factors, but sleep deprivation is frequently cited as one of (if not the biggest) reason for why it happens. Being exhausted all the time will do your physical and mental health no favors, but depriving your brain of restorative sleep will eventually cause you to stop caring about work altogether. Your mood is tightly linked to your sleep patterns, and if you find yourself more irritable or short-tempered than usual, consider going to bed earlier.

Worsening memory

Memorizing a lot of information is never easy. Doing it on four hours of sleep is nearly impossible. While the link between sleep and memory is not fully understood, chronic sleep deprivation has been shown to correlate with a reduced overall ability to form and retain memories over the course of a lifetime. It’s speculated that the brain transitions short-term memories and information over the course of the day into longer-term memories during sleep, which is why people that aren’t getting enough sleep tend to underperform at school and work overall.

Don’t treat a lack of sleep as though you are wearing some kind of badge of honor. There’s a reason we evolved to need the amount of sleep that we do, and while its exact role in regulating biological functions isn’t fully understood, it is shown to be highly correlated to your mood, weight, concentration, and memory. Getting five hours of sleep as opposed to eight might seem like a good deal on paper – you get an extra three hours to do anything you want! The actual reality is that your decline in productivity as a result of feeling so tired will eventually cancel out the extra time you have. One night of doing this won’t kill you, but over time it adds up to a significant deficit, one that winds up negating everything you thought you gained by sleeping less.