Caffeine can be very effective for improving your concentration, alertness and energy. However, if you consume caffeine on a daily basis these positive effects can be brief and it can reduce the quantity and quality of your sleep. If you use caffeine to counter tiredness, feeling sluggish, or difficulty concentrating it could also be masking a sleep disorder (or it could be making the sleep disorder you have more difficult to manage). Caffeine is a stimulate and acts as an “adenosine receptor antagonist.” Adenosine is a substance in your body that promotes sleepiness. Caffeine blocks the adenosine receptor to keep you from feeling sleepy. The effects of caffeine reach a peak within 30-60 minutes. The half-life (the time it takes for your body to eliminate half of the drug) is 3-5 hours. The remaining caffeine can stay in your body for up to 24 hours. This can have a disruptive effect on your sleep. One study has found that caffeine can actually delay the timing of your body clock. The effects of caffeine can even occur when you consume it earlier in the afternoon or evening. A study published in the journal, Sleep found that consuming caffeine 6 hours before bedtime reduced total sleep time by 1 hour. These effects also can be stronger in older adults as it takes their bodies a longer time to process caffeine.
Caffeine can make it harder to fall asleep and it can reduce the amount of deep sleep you have so it can also make staying asleep difficult.
Did you know that while caffeine can boost energy levels and make you feel more alert caffeine intake can also result in you feeling sleepy – something people with sleep disorders, particularly idiopathic hypersomnia and narcolepsy do not need! Check out this Healthline article to find out why your regular caffeine hit could be contributing to your sleepiness. And if you take stimulate medication check out our article "Why is my Dex not working". What your eat and drink and the timing can have bigger impact on the effectiveness of your medication than you may realise.
If you must have a cup of coffee in the morning you should try to wait at least an hour after waking. Cortisol is a hormone that can enhance alertness and focus. It also regulates your metabolism, immune system response, and blood pressure. It follows a rhythm specific to your sleep-wake cycle with high levels that peak 30–45 minutes after rising and slowly decline throughout the rest of the day. According to chronopharmacologists, who study the way drugs (such as caffeine) interact with our body’s natural biological rhythms, consuming caffeine while our bodies are at peak cortisol-production teaches the body to produce less cortisol. This not only undermines the effect of the caffeine, it also works against cortisol’s alertness effect. It may also contribute to you developing a tolerance for caffeine which means if you use it to help your stay alert and focused you will need to consume more and more of it to get the same effect - and more caffeine is definitely not what you should be aiming for.
Too much caffeine (along with too much stress) can also take a toll on your adrenal glands. Poorly functioning adrenal glands, in turn, can damage the immune, cardiovascular, neurological, and endocrine systems, and, eventually, your long-term health. If you rely on caffeine to help you concentrate, to boost your energy levels or to keep you feeling more alert during the day speak to your doctor. Caffeine could be masking an underlying sleep disorder or it could be making the sleep disorder you have more difficult to manage.
Updated 6 Jan 2021, originally written for the 2018 Australian Sleep Awareness Week. The theme was caffeine and the role it has on society.
Information sources (other than those mentioned in the article):
“Sleep Education” a resource provided by AASM.
Chan S, Debono M. Replication of cortisol circadian rhythm: new advances in hydrocortisone replacement therapy. Ther Adv Endocrinol Metab 2010;1(3):129-138.
Lovallo W, Whitsett T, al'Absi M, et al. Caffeine stimulation of cortisol secretion across the waking hours in relation to caffeine intake levels. Psychosom Med 2005;67(5):734-739.