Ask a Dietitian: Does Caffeine Really Affect My Sleep?

We drink coffee and other caffeinated concoctions because of their stimulatory effects. Many of us have come rely on caffeine for increased alertness, improved cognition and better exercise performance. Delicious and effective? Sounds too good to be true.

A morning coffee is the kick-start we need to get going; an afternoon coffee is the pick-me-up we can't live without. The same mechanisms that benefit our energy levels during the day, however, can be detrimental when we're trying to sleep at night. 

Let's investigate how caffeine affects sleep by looking at three chemicals that are naturally active in the human brain:

1. Adenosine

Adenosine can act as a central nervous system depressant, promoting sleep and suppressing arousal. The level of adenosine in our brain builds up over the course of the day, making us feel more tired and less alert by the time evening rolls around.

2. Dopamine

Caffeine has a sort of disguising effect on our adenosine levels, causing downstream effects on other sleep neurochemicals. Just like addictive drugs, caffeine can also increase dopamine levels. Not only do we feel more alert but we can also experience a sort of high, and these effects combined contribute to the addictive quality of coffee and other caffeinated drinks.

3. Melatonin

The brain chemical melatonin is also impacted by caffeine. You may associate melatonin with the light–dark sleep cycle, but caffeine also has a strong influence on melatonin release. To add to this, the diuretic effect of caffeine can also see your sleep being disrupted for trips to the bathroom. High doses of caffeine not only make it difficult to fall asleep but also to stay asleep through the night.

When it comes to caffeine, how much is too much is really going to differ from person to person. Some people are just much more sensitive to caffeine than others. Of course, how often and how much we consume caffeine has an impact on our sensitivity to it – habitual intake tends to reduce your sensitivity, whereas someone who only drinks the occasional coffee is likely to feel its stimulatory effects much more intensely.

The peak concentration of caffeine in the blood stream typically occurs between 30 and 70 minutes after consumption, but the effects of caffeine can last between three and seven hours, and it could take up to 24 hours for caffeine to completely disappear from our system. That means that a dose of caffeine in the evening might reach its peak effect when it's time to go to sleep. Not ideal.

But how much caffeine am I consuming?

The amount of caffeine in a food or drink varies substantially. A product such as No-Doz consistently contains 100mg of caffeine per tablet, whereas such as coffee and tea are much harder to quantify. An instant coffee may contain anywhere from 65-100mg of caffeine per cup, whereas a brewed coffee anywhere from 80-350mg per cup. Even decaffeinated coffee still contains some caffeine. Other caffeine sources include soft drinks, energy drinks and even chocolate.

It's understood that between three and six milligrams per kilogram of body weight will improve cognitive and exercise performance. For someone who weighs 80kg, this means 240-480mg caffeine per day. But if you're buying coffee from your local barista, it's hard to know just how much caffeine you are actually consuming. Exceeding the 6mg/kg can not only lead to poor performance and sleep but also cause jitters, increased heart rate, anxiety, stomach pains and headaches.

So if you're having trouble falling asleep or staying asleep and think it could be caffeine related, the general rule of thumb is to avoid caffeine after 2pm. This should allow enough time for the stimulatory effects to wear off, and your body's natural sleepiness to hit.

So, keep your morning coffee, but take steps to skip the afternoon dose if you want to sleep better at night. For caffeine-free afternoons, avoiding artificial sugars (generally, but especially at lunch) and when you do start feeling groggy mid-afternoon, eat an apple. While it's not true that apples actually contain caffeine, they do contain natural sugar and vitamins that are released slowly throughout the body, making you feel more awake. Without this afternoon dose of caffeine, you'll likely sleep better and wake up the next day more rested than ever.

Explore more content like this in our series, Ask a Dietitian. 

Health & Performance Collective is the brainchild of Sydney Dietitians Jessica Spendlove and Chloe McLeod. They use their 20 years of combined knowledge and skills as dietitians to work with motivated people to live and perform at their best.

Still not sleeping well? You might be eating the wrong foods before bed.