Is coffee bad for your immune system?

Qualified Nutritionist (BSc, MSc, RNutr)
Ask Emma

11 September 2021

Is coffee bad for your immune system?

Whilst coffee contains some helpful antioxidants, the high caffeine content of coffee may outweigh the benefits. The caffeine content of coffee means that is stimulates your stress response, whilst also potentially having negative effects on your sleep – another key regulator of your immune function.

Why too much coffee is bad for your immune system

Too much coffee may be detrimental due to its high caffeine content. Some negative effects of coffee on your immune system include:

1. It ignites your stress response

Coffee is a rich source of caffeine, with some coffees prepared at commercial coffee houses thought to contain up to 400mg of caffeine per drink! Teas, for example, also contain varying degrees of caffeine, although generally at much lower levels - around 50mg, on average, per serving.

Research has shown that caffeine intake causes an increase in cortisol levels. (1) Cortisol is our main stress hormone that encourages your body into its 'fight or flight' mode. Unfortunately, being in your fight or flight mode when the sympathetic branch of your nervous system is most active, doesn't spell good news for your immune system. Your immune system generally works best during a state of relaxation (hence why adequate sleep is so important).

There has been some suggestion from the research that small intakes of caffeine (therefore creating a little stress) could be stimulatory for the immune system, (2) and therefore potentially helpful.

However, when we switch to having too much caffeine, this could risk decreasing your immune system's ability to fight off infections, although the evidence on this front has been done on small sample sizes only and so may require further study. (2) However, the general consensus is that chronic stress, isn't so helpful. (3)

2. It could affect your sleep

As well as risking putting you into a more prolonged state of stress during your waking hours, too much strong coffee could also affect your ability to nod off at night.

Research has shown that coffee intake accounted for 15% of the total cortisol levels found in subjects at night (when cortisol would naturally be dropping off at this time) (3) which could easily be an unhelpful contributing factor if you struggle to nod off. We also shouldn't forget just how long caffeine can remain in your system – up to 10 hours in some cases! (4)

We're well aware how important a good night's sleep is for protecting your immune function. Sleeping well, but also at the correct times, seems to have positive effects on many of your important immune cells, such as killer T cells, but is also beneficial for helping to keep pro-inflammatory cytokines in check – immune-modulation really is key. (5)

But does coffee have any benefits for the immune system?

So, where has the idea come from that caffeine, and in this case coffee, could actually be helpful for immune health? I've certainly seen caffeine listed on come conventional cold and flu meds, plus, does coffee itself have any additional benefits, outside of the caffeine content? Let me explain:

1. The antioxidant potential

The idea that coffee is a useful source of antioxidants is an interesting theory and seems to be a possible mechanism for some of the more frequently proposed positive actions. However, interestingly this can vary quite considerably depending on the quality of the coffee; plus, the degree of roasting makes a difference – dark roasts, for one, tend to lose more of the antioxidant and anti-inflammatory potential. (6)

The antioxidant capacity of coffee is only one consideration, of course; it really remains to be seen how this dose of antioxidants compares to other antioxidants without all the caffeine...

What's the solution?

Would other sources of antioxidants, without the debatable caffeine content, be a more suitable option? Green tea, for one, has been largely studied for its immune-balancing potential and crucially, its lovely balance of phytochemicals means it does appear to be gently immuno-modulating. (7)

This is absolutely crucial; see, we want our immune system to work appropriately when we have an infection, but not to be over-stimulated otherwise.

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2. Is its stimulatory action a good thing

We know caffeine is generally 'stimulating' but in terms of its effect on the immune system, this is up for some debate. The consensus seems to be that that drinking a little coffee may be ok (but then there are perhaps even better alternatives out there), but then, when one switches over into becoming a chronic coffee drinker, the proposed risks soon start to outweigh the benefits. These effects may also be dependent on how good quality your coffee is to start with, so it isn't completely clear cut.

What's the solution?

When I consider if a little bit of stress could be considered a good thing I instantly think of the effects of exercise on the immune system. Exercise has undeniably been shown to be good for our immune function, and this is thought to be down to the immune-stimulating effects that comes after a short bout of stress – exercise.

So, unless you go to extremes with your movement, which then may prove to be more complicated in terms of the perceived benefits for your immune health, a little bit of stress isn't always a bad thing.

So, much like the exercise theory, research has shown that any perceived benefits of drinking good quality coffee may start to wain after 2 cups. (8)

The conclusion? More is not always better! So, if you like your cuppas, substituting for a healthier, herbal alternative may be best, and especially beyond a certain point.

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