How Much Does Caffeine Affect Sleep, Really?

We have written before about the health benefits (and risks) of coffee; for most people, the benefits far outweigh the risks, but individual cases may vary:

The Bitter Truth About Coffee (or is it?) ← this is a mythbusting edition

Speaking of bitterness; coffee has abundant polyphenols, which means an abundance of benefits that we discuss in the links above and below this line 😉

See also: Why Bitter Is Better: Enjoy Bitter Foods For Your Heart & Brain ← while it says foods in the title, this does cover coffee too.

For mythbusting on caffeine specifically, enjoy: Caffeine: Cognitive Enhancer Or Brain-Wrecker?

There are also gut health benefits from drinking coffee, and what’s good for our gut is invariably good for our heart and brain:

Coffee & Your Gut ← gut bacteria do not, by the way, have a preference about how you make your coffee or whether it is caffeinated or not

Aaaaaand, we recently shared new research on how coffee appears to be protective against frailty in older age. We say “appears to be”, because it was a longitudinal study and so technically we cannot say categorically that the link was causal, but the association is very strong, to the point that it’d take quite some explaining if it’s anything other than the coffee consumption that caused it.

You can read about that here: Coffee vs Frailty!

But what about sleep?

Common sense has of course long served to tell us: taking a stimulant before bed can disrupt your sleep. Shocking, breaking news!

Except, even we at 10almonds have never actually examined the science for this. After all, it seems so obvious; it’s like how one does not need a peer-reviewed study to conclude that water is wet.

However…

A study was conducted, and found that, upon investigating, caffeine indeed disrupts sleep, by an average of two hours per night!

Except…

That study, from 1974, had 6 participants (in fact the abstract says “subjects”, but that is how scientists referred to people in the 70s), and the methodology went:

❝…comparison being made with decaffeinated coffee and with no drink prior to sleep, using each condition five times in a balanced order on non-consecutive nights.

After caffeine the mean total sleep time decreased on average by 2 h, the mean sleep latency increased to 66 minutes. The number of awakenings increased and the mean total intervening wakefulness was more than doubled after caffeine.❞

Read in full: Effect of caffeine on sleep

Did you spot the problem? Aside from “n=6 is not a relevant sample size”… The methodology of using each condition five times in a balanced order on non-consecutive nights means that not only did they completely break from placebo (there is no mention of whether they even tried to blind or double-blind this) but also, think about this:

• It’s your first night at a sleep clinic. You take caffeine before bed, and you don’t sleep well; perhaps because of the caffeine or the strange environment.
• It’s the next night at a sleep clinic. Last night you slept 2 hours less than normal, so you absolutely crash out this time, and sleep extra to compensate.
• It’s the third night at a sleep clinic. Having overslept the previous morning, you’re not too tired tonight, and so you don’t sleep as much.
• The study only lasts 10 days so this pattern doesn’t get a long time to diminish.

See also: What’s Really Keeping You Awake? The Brain’s Role in Sleepless Nights

A more recent study was almost equally tiny (n=10) because it was just a pilot study, but used a better methodology with a double-blind control group design. For the first 7 days, all participants consumed caffeinated coffee. In the following 7 days, subjects consumed caffeinated or decaffeinated coffee according to their assigned group. This study found:

❝There were no significant differences (p > 0.05) among the data of the two groups identified. No significant changes (p > 0.05) were found in the sleep quality of either group during the study.

This study confirms that caffeine abstinence in the evening might not be helpful in sleep promotion. It highlights the need to implement evidence-based practice in health promotion.❞

Read in full: The effects of caffeine abstinence on sleep: A pilot study

What caffeine actually does, in the context of sleep

Now we’ll get into some meatier science, by which we mean that the same size is enough (n=40) to give us real statistical significance, and also it compared the effects on younger adults (20–27 years) and middle-aged adults (41–58 years), and monitored their brains with electroencephalography (EEG) during REM sleep and non-REM sleep.

They found:

• Caffeine reduced alpha and theta waves, linked to deep sleep.
• Caffeine increased beta waves, associated with wakefulness* and mental activity.

*Note: it increased these beta waves during sleep. It did not affect sleep quantity, it merely changed its quality. And, not necessarily badly, because that’s needed too (such as for memory consolidation and other mental faculties), but meaningfully.

They also found that these effects were more pronounced in young adults (ages 20–27) than in middle-aged participants (41–58).

You can read the paper in full here: Caffeine induces age-dependent increases in brain complexity and criticality during sleep

And you can learn about brain waves during sleep, here: Alpha, beta, theta: what are brain states and brain waves? And can we control them?

And for getting into hacking some of these: Non-Sleep Deep Rest: A Neurobiologist’s Take ← How to get many benefits of sleep stages, while awake!

We’re running out of space today, but before we go, we’ll mention this larger (n=99) longer (12 months) study into matcha green tea instead. Of those 99 participants, the study included 64 with subjective cognitive decline and 35 with mild cognitive impairment; these were randomized, with 49 receiving 2 g of matcha and 50 receiving a placebo daily, and to quote from the conclusions in the paper:

❝Despite the presence of caffeine, which disrupts sleep, matcha demonstrated a sleep-enhancing effect. This beneficial effect is attributed to theanine, a constituent of matcha.

The present study suggests regular consumption of matcha could improve emotional perception and sleep quality in older adults with mild cognitive decline❞

Read in full: Effect of matcha green tea on cognitive functions and sleep quality in older adults with cognitive decline: A randomized controlled study over 12 months

Don’t love coffee?

Two excellent alternatives are green tea (and/or green tea extract), and green coffee extract. You can read about them both here:

• L-Theanine: What’s The Tea?
• Green Coffee Bean Extract: Coffee Benefits Without The Coffee?

Enjoy!