Caffeine is the most widely consumed psychoactive substance in the world. Many people rely on it to improve their alertness and cognition, especially when they are feeling low energy or run-down. This is why the following is particularly relevant, especially considering the global climate when caffeine's effect on the immune system could have more serious consequences.
What is caffeine?
Caffeine is a substance produced by plants as a defence mechanism to prevent insects from eating their leaves and seeds, as well as enhancing the reward memory of pollinators to ensure increased reproduction.
In humans, the build-up of a substance called adenosine is one mechanism that induces a feeling of fatigue and encourages us to sleep. Adenosine binds to receptors (like a key in a lock) which causes us to feel tired, slowing neural activity. Caffeine works by fitting in to the same receptor like a skeleton key, preventing adenosine from binding to the receptor and having an effect. This inhibits the adenosine molecule's action without reducing neural activity and thereby provides relief, albeit temporary, from fatigue.
This clearly has its uses, but also its abuses, with millions of people across the world relying unhealthily on this substance to stave off feelings of tiredness and the cognitive disruption that comes with it.
When the caffeine wears off, the tide of adenosine comes back in full force and can leave one feeling even worse.
This can result in a circle of dependence where many become addicted and reliant on the effects of caffeine as well as experiencing further negative effects if they haven't had their routine shot of caffeine.
What does this have to do with the immune system?
One of the effects of caffeine is that it increases the release of cortisol in the body.
This so-called stress hormone has a depressive effect on lymphocyte activity, especially if raised chronically (as it is in those who consume too much caffeine). Lymphocytes are paramount for the adaptive immune system,one way in which the body prevents new threats from growing.
The majority of caffeine is broken down in the liver over a 5 hour period on average. Once broken down, the main metabolite is called paraxenthine. Paraxenthine is one component of caffeine that affects the immune system.
Paraxenthine does stimulate fat loss, however it also suppresses monocyte (white blood cell) and neutrophil production, both of which are extremely important for the immune system.
Finally, caffeine has been shown to reduce antibody production which is the main weapon against new pathogens including viruses.
Caffeine and the immune system
So what does this all mean for me?
Caffeine is an effective tool for when you are feeling a bit tired day to day, or if you need a bit of extra stimulation for a special project.
However, everyone should be aware of the downsides to the most popular drug in the world. Everything comes at a cost and caffeine may reduce your immune system by around 30% as well as having negative effects on your adrenal response and ability to fight tumours.
A popular alternative is green tea, with less caffeine, it still has stimulation effects and no negative immune system suppression.
Most importantly, if you are unwell or feeling run down (and therefore more susceptible to illness) reaching for that cup of coffee may not be the best idea!