After we have woken up we start to build up our sleep drive ready to sleep later that day. When we are awake we are producing a sleep chemical called adenosine. When we have built up sufficient stores of adenosine, have a good functioning sleep/wake cycle and are not anxious then we will fall asleep.
During our sleep adenosine will leave our bodies so we should wake up feeling alert and ready for the day ahead.
When we consume caffeine it acts on our brains by blocking our adenosine receptors. As a result, it masks our tiredness. It’s a bit like pressing the mute button on a remote control, the program is still playing we just can’t hear it. When caffeine is present in our brains we still have our stores of adenosine and they will still continue to build up but we don’t feel tired.
The issue arises when the effect of the caffeine wears off as all of our stored adenosine floods our brains which can lead to a caffeine crash. This means we will often feel even more tired than before we consumed the caffeine. We might then find ourselves consuming more caffeine to increase our alertness and so the cycle continues.
Caffeine is a stimulant, it acts on our nervous system increasing our breathing and heart rates and making us more alert. It has a half-life of roughly 5 to 6 hours. This means that half of the caffeine you consumed will still be in your system 5 or 6 hours later and a quarter of it will still be remaining some 12 hours later.
If you are consuming caffeine late in the afternoon or evening, then you will be trying to sleep with a stimulant still acting on your body.
Caffeine is also a known anxiogenic, meaning that it can cause or enhance anxiety. In order to sleep we need to be unaroused. If we are anxious we will often find ourselves lying in bed worrying about the future. Whilst it might not be that your caffeine consumption has been the sole contributor to this situation, it is certainly possible that it has been a contributing factor.
Some people appear to be less prone to the stimulating effects of caffeine and can drink coffee late in the evening and still fall asleep. Recent research has however revealed that caffeine will still affect these people’s sleep. If you consume caffeine late in the evening your deep sleep will be shortened by somewhere between 15-30%. Our deep sleep has many functions including regulating our cardiovascular and metabolic systems, replenishing our immune system, consolidating our memories and cleansing the brain of toxins that can lead to conditions such as Alzheimer’s disease.
Whilst it would be hard to argue that caffeine has any beneficial effect on our sleep, coffee is an antioxidant and so can help our bodies fight disease. As it is also derived from a plant source it is thought that it can help to positively enhance our gut microbiome.
If you are finding it difficult to sleep or are currently experiencing anxiety the general recommendation is to lower your consumption of caffeinated drinks to 2 or 3 and not to consume them in the afternoon or evening.
Perhaps you might be interested in reading other articles from my mini-blog series;