Sleep is the foundation of human health and performance. It keeps us healthy, emotionally stable, intelligent, creative, attractive, and accident-free.

As the world slowly catches on to this foundational truth, the internet is filling up with sleep advice. But there’s a problem: very little of this advice is backed by any quantified proof.

That’s why I decided to quantify the effects of various lifestyle choices on my sleep quality. My daily choices are recorded on my Graph of Life, and my sleep quality is quantified via Sleep Cycle.

Let’s see what the data has to say.

The Results

I performed an analysis of the statistical correlations between the wide range of lifestyle metrics I collect on a daily basis and my sleep quality. The five most important correlations are given below, together with two obvious requirements for high sleep quality: duration and consistency.

Let’s take a look at each of the factors in turn.

Time in bed

The dashed green line shows the high correlation of sleep quality with the amount of time spent in bed. This one is obvious: I only sleep when in bed, so enough time in bed is a prerequisite for high sleep quality.

Consistency

One of the first things you’ll see in any sleep hygiene article is the need to maintain a consistent sleep schedule (even on weekends). I quantified this metric by comparing the standard deviation of my sleep duration to my average sleep quality over each week.

As shown by the orange line, sleep consistency is about half as important as sleep duration. Interestingly, the correlation of sleep duration (0.40) with consistency is even higher than sleep quality (0.33). This means that poor consistency strongly reduces the time I spend in bed.

It makes good sense: With all the demands of modern life, consistency is the only way to make enough time for good quality sleep.

Eating habits

I’ve previously established that eating habits are the single biggest factor in the quality of my day. For this reason, I was not overly surprised when it again emerged as the winner in this case.

The graph shows that good eating habits are even more important than consistency when it comes to sleep quality. Delving a little deeper, I saw that this effect was split equally between two factors:

1. Time in bed (correlation = 0.28). My eating habits are a good indication of my general level of discipline on any given day. Poorer discipline often means that I get in bed too late, giving me fewer hours to sleep.
2. Sleep efficiency (correlation = 0.26). The ratio of sleep quality to time in bed also reduces substantially with poor eating habits, resulting in less restoration for every hour spent in bed.

We can also see that a good night’s sleep causes better eating habits the following day. It’s well-known that an underslept mind leads to more food cravings as well as cravings for the wrong kinds of food (see the “obesity and diabetes” section in this article).

Checklist

My checklist is a direct indication of the number of things I did right on a particular day. Many of my checklist items are recurring productive and healthy actions, keeping me firmly on the straight and narrow.

The graph shows that ticking many items off my checklist is both a cause and an effect of high sleep quality. It’s easy to imagine how a good night’s sleep would improve my ability to get things done the next day, but I was a little surprised that this was also such a significant cause of good sleep.

But there is a logical explanation, and it looks quite similar to the one given above for the effect of eating habits:

1. Time in bed (correlation = 0.23). Like eating habits, my checklist is a good indicator of discipline, which affects my sleep duration.
2. Sleep efficiency (correlation = 0.23). A productive day seems to make each hour of sleep more restorative. This must be related to that tired-but-satisfied feeling typical at the end of a successful day. It’s easy to imagine this pleasant feeling leading to better sleep.

Work

The effects of work on sleep can be interpreted similarly to the effects of my checklist discussed above. However, the correlations are considerably smaller. This is because my checklist is a more holistic indicator of whether I did the right things during the day than my work performance.

Even though the correlations are smaller, they clearly show that prioritizing sleep is good for productivity. This confirms that sleeping less in pursuit of greater productivity is a terrible idea.

Excercise

Regular exercise is sometimes recommended as a sleep aid, but the graph shows that this was not the case for me. In fact, this is the only statistically insignificant (p > 0.05) correlation in this analysis, implying that the little blue bar in the graph could just be random.

However, a good night’s sleep helps me exercise the following day. This is also no surprise given that physical performance improves significantly with sleep (see the “motor memory” section in the aforementioned article).

Energy

The relationships between my energy levels and sleep quality look similar to the correlations with exercise: High energy levels are an effect of good sleep quality rather than a cause.

It makes sense that a well-rested body and mind will feel more energetic. The correlations are stronger than those of exercise because my subjective energy score includes both mental and physical aspects.

Other important factors

Sleep quality also depends on several other factors that I could not quantify due to a lack of data. Let’s take a quick run-through:

• Wind-down routine. This is something I’ve only started doing recently and I don’t yet have data for it. My feeling is that this does help a bit, but it doesn’t perform miracles. Next year, I’ll have the data to confirm.
• Smoking and alcohol. Both of these are said to be bad for sleep. I don’t smoke and very rarely drink, so I lack the data to quantify this.
• Coffee. No coffee after lunch is another commonly listed sleep hygiene guideline. I’m a (caffeine-free) tea-person, so no data here either.
• Bed and pillow. Another obvious bit of advice is to maximize the comfort of your bed. Some years ago, I often woke too early with neck pain. Luckily, this was quickly fixed with a fancy memory foam pillow.
• Light and temperature. A cool and dark room is another common piece of sleep advice. Over here in Norway, both light and temperature vary greatly over the seasons, but I see no clear drop in my sleep quality during summer months. I do use a sleep mask in summer, but I make no attempt to control the temperature in my room.
• Noise. Sleeping in a noisy environment is tough. Luckily, I live in a quiet neighborhood with few disturbances. There is a bit of noise from neighbors on rare occasions, so I can still collect some data next year.
• Scents. I have some lavender pillow mist I remember to use every once in a while, but I don’t collect data for it. I doubt that the effect is significant, but I still plan to investigate this properly next year.

The Takeaway

Start with the big two: duration and consistency. After that, my experience shows that good eating habits and a productive day are the next two best inducers of a good night’s sleep.

Otherwise, there is a range of additional factors whose influence I’m yet to calculate. Most of these are obvious, such as a cool, dark, and quiet room with a comfortable bed. Others, like a wind-down routine and aromatherapy, will be interesting to investigate further in the future.

Sweet dreams!