Hey Insiders,

This is the third edition of our Wellness newsletter.

Today we’re covering something investment bankers have a love-hate relationship with. And no, it’s not your managing director or your girlfriend.

A Deep Dive into How Much Sleep You Need

The Science of Sleep

Sleep can be a touchy topic, particularly for our young professional audience, for whom it can always seem to be in short supply.

But exactly how much sleep do you need? What’s the least you can get away with? And what can you do to perform your best if there’s simply no way to get your recommended hours?

For starters, the easy question: how much do you need? You’ve probably heard it everywhere, from high school health class to your mother’s worried phone calls: You need 7-9 hours of sleep.

Hitting this range of shut-eye produces benefits that are well documented by scientific studies.

Sleep Benefits

During sleep, your brain activity changes drastically. 

As you move through deep and REM sleep stages during a night of shut-eye, your brain performs different functions. REM sleep is probably the most important of these, since your brain takes key steps to preserve mental health and acuity. The exact mechanisms aren’t completely understood, but we know that REM sleep is associated with the separation of emotion from memories, an important step in emotional wellbeing. 

These findings are corroborated in studies of victims of PTSD, who experience very little REM sleep and can’t adequately process intensely emotional memories. While we hope you haven’t been through anything severe enough to induce PTSD, the benefits for your wellbeing are valid for any level of emotional intensity. 

Besides emotional wellbeing, your brain fires in unique patterns while you are asleep. The thalamus becomes quite active, sending the cortex images, sounds, and other data that appears in dreams. 

Particularly during non-REM sleep, brain activity fires in patterns known as spindles and K-complexes. These patterns are believed to be related to the consolidation of memories and the formation of new connections as a result of these intense firing patterns, which connect areas of the brain that don’t typically work together during waking hours.

Finally, deep sleep is key to your physical recovery. Your body repairs injury, begins new tissue growth, and cleans out waste products. You will notice a greater proportion of your sleep is spent in the deep sleep zone if you increase the intensity of your workout routine, a natural reaction to the heightened need for restoration. 

Under-Sleeping

Just as the benefits of sleep are well-documented, so are the negatives of missing out on your daily dose of shut-eye. 

Getting less than the recommended 7-9 hours can have insidious effects. Cognitive function, heart health, metabolic function, reaction time, and mood all decline dramatically when you aren’t well rested. 

Perhaps worse than these “day-after” effects are the longer-term effects. The downsides of getting less than 7 hours of sleep on a given night may be imperceptible the next day, meaning that you might not even notice if you have lower cognitive function or physical recovery.

This can lead you to assume you are getting away with the shorter sleep schedule, pushing the envelope further and creating a reinforcing cycle where the daily changes in functioning ability go unnoticed until you end up with a much worse condition than you had in your fully-rested state.

Studies show that those all-nighters are even worse than you realize. Being awake for 24 hours straight leads to the same cognitive impairments as someone with a 0.10 BAC - which is above the “legally drunk” threshold required to drive. 

Besides mental impairment, men who only got five to six hours of sleep displayed the same levels of testosterone equivalent to someone 10 years older than they were in clinical studies. So sleep deprivation is brutal if you’re looking to accomplish anything meaningful in the gym. Sleep deprivation has been shown to cause you to lose muscle and gain fat, which is probably the exact opposite of what you’re going for. 

We were surprised to learn just how large these effects can be. A 15% increase in all-cause mortality is associated with sleeping 5 or fewer hours over a long period. This means that you have a 15% greater chance of dying by any cause if you sleep this little. 

The upshot is that the 7-9 hour general guidance has been well-supported through decades of research. Missing this target means you are missing out on a multitude of benefits and exposing yourself to quite a bit of risk over time. 

A Caveat

It is important to realize, notes Eric Zhou of Harvard Medical School, that 7-9 hours is a general guideline. This means that some people can function without impairment while sleeping less than 7 hours, while some need even more than 9. This has been observed anecdotally for years, but the mechanisms behind it are just now being revealed. 

New genetic research finds that “There is a small percentage of adults who don’t require the recommended seven hours of sleep each night. Someone like this is called a short sleeper, and they function well during the day even after sleeping less than six hours a night.”

Some studies have proposed that a specific DEC2 gene mutation correlates with the ability to function on very little sleep. Although the specific genetic mechanisms are not completely understood, the observance of this phenomenon is a notable break from the conventional 7-9 hour guidance.

While these new studies are interesting, it may be less exciting on a personal level. It is unlikely that these new findings are enough evidence for you to toss out the standard 7-9 hours. 

The percentage of individual adults who are short sleepers, meaning they see zero impairment from getting less than six hours of sleep, is very, very low. While you might be one of this fortunate few, the statistics make this unlikely.

Sleep Quality

The data is clear: you should do what you can to get at least seven hours of shut-eye per night. Whether this means rearranging your errands, ordering food instead of cooking, or making other adjustments to your life, it can be well worth it for the mental and physical health benefits.

However, even if you can’t reasonably expect to be in bed for more than 7 hours with your work schedule, there are still steps you can take to promote wellness and ensure you’re performing your best.

In fact, Zhou also notes that quality of sleep can be quite important in how you feel during the day. An increasing body of research is supporting this statement. 

First, make sure your environment is set up correctly. Studies find that the optimal temperature for sleep is around 65 degrees Fahrenheit (or 18.3 degrees Celsius). 

This too may vary between individuals, so start setting your thermostat around this level and then test slightly lower or higher temperatures to see what feels best for you.  

Additionally, especially if you live in a city, there are probably lights and other disturbances that can seep through your windows. Consider purchasing blackout curtains. 

These will help prevent disruptions that can wake you in the night as well as blocking out bright lights that may disrupt your circadian rhythm as you work your way towards bed time.

Speaking of which, try to wind down as your day comes to a close. Avoid strenuous physical exercise, heavy meals, mentally taxing activities, and bright lights for at least an hour before bedtime. 

Consistency

Before you make getting 7-9 hours of sleep your be-all, end-all, experts say there’s a different metric you should be prioritizing.

Sleep consistency - going to bed and waking up at roughly the same time every single day - is more important than the specific quantity of hours you’re getting.

To put this into perspective - science shows that only getting six hours, but getting up and going to bed at the same time every day - is healthier than getting eight hours, but on a less consistent schedule. 

A 2024 study analysis by the Journal Sleep says, “Emerging research demonstrates that sleep regularity, the day-to-day consistency of sleep–wake timing, can be a stronger predictor for some health outcomes than sleep duration.”

The study adjusted for age, ethnicity, socioeconomic status, and lifestyle factors and concluded that sleep regularity had a larger effect on reducing all-cause mortality than overall sleep duration.

This means that, even if your job pushes you to work long hours, you can optimize your performance during waking hours and feel (a little) better by trying to fall asleep and wake up on a regular schedule. 

While you won’t get all the recovery benefits of a full night’s sleep, you can decrease the acute health risks and optimize your waking functionality. 

Conclusion

Overall, the amount of sleep you need is mostly fixed. While this is unfortunate for those of us who feel that there is never enough time in the day, it is important to be mindful of this requirement. The long term risks of increased stroke, heart attack, diabetes, and depression are too great to ignore.

If you are one of the professionals with a work schedule that is truly so demanding that there is no way to leave sufficient time for sleep, consider focusing on your sleep regularity. While you may still feel irritable and frustratingly tired, rest assured that this regularity can significantly counteract the negative health effects that would otherwise be inevitable in a chronically under-rested state. 

Ultimately, as with all things, the sleep equation is a risk-reward tradeoff. It can be worth it to sacrifice some sleep and therefore decrease your health while you are young in order to boost your chances of reaching your long-term career goals. While we suspect many of our readers are in this boat, this is a very personal decision that you ultimately have to judge for yourself. 

For those who aren’t working such aggressive hours 1) jealous! And 2) try to ensure you’re following the rest of the advice regarding quality and regularity, since spending 9+ hours in bed is no good if your sleep quality is so poor that you aren’t getting the associated restorative effects.

Let us know which of these findings you found most surprising, and what steps you can take to boost your sleep quality.

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