My favourite part of waking up is going to the freezer and getting my coffee beans, weighing them out and grinding them up. I love coffee and I know many millions of others do too. One question I get a lot is: ‘Does coffee dehydrate you?’.
No it doesn’t. But I understand why you may think it does.
We’re told to drink so much water every day. As coffee is a diuretic you may think it does dehydrate you. Or you may think it doesn’t count as part of your daily fluid intake.
Well, it does. But before you start drinking 2 litres of coffee every day. I want to explain why it does count. But I also want to explain why you don’t want to only drink coffee. Then finally, I want to explain how you can go forward with your coffee drinking endeavours.
So coffee may not dehydrate you, but you may still want proceed with caution.
What is dehydration?
Dehydration is the state at which more fluid leaves the body, than what comes in.
To be adequately hydrated, you want to be in a state where equal fluid is being drunk, to what is leaving your body. (1)
Even though adults are at risk of dehydration. Dehydration is a greater risk to children, babies and the elderly. (2)
What causes dehydration
Water loss in of itself is not a great concern. This is because water can easily be replaced. Yet, if the water isn’t replaced, this is where you may run into some issues, such as dehydration.
There are various causes of water loss, though these are the main ones:
- Not replacing the lost water
- From the skin
- Water loss from the kidneys
- Gastrointestinal tract
- Intra-abdominal issues
As you can see, it’s not exactly coffee that will dehydrate you.
Not replacing the lost water
Though it sounds obvious not replacing the water you lose through sweating, urinating and other body functions, you run the risk of becoming dehydrated.
Water loss from skin
Water loss from skin can happen for various reasons, such as:
- Skin diseases
As mentioned above, if you replace the fluid lost, these shouldn’t be a major concern. Obviously if you do have or show symptoms of burns or skin disease, please go visit your healthcare practitioner.
Water loss from kidneys
The kidneys can be a great cause of water loss. This can stem from issues such as various renal diseases, or taking medication. (4)
GI issues can also lead to dehydration.
GI issues such as chrones disease or inflammatory bowel disease are especially known to cause dehydration. Symptoms usually include Diarrhoea or vomiting. This is because they cause the body to lose a large amount of fluid.
Diarrhoea prevents the large intestine, from absorbing water from your food. Though you may think food is solid, as large bulk of what you eat is water. Think of most the fruits and vegetables you eat.
If the intestine isn’t absorbing that water, theres only one other place it can go. (5)
Intra abdominal issues
These can happen after surgery or due to another condition. Conditions such as appendicitis or diverticulitis. (6)
Though there are many symptoms, one symptom is vomiting. It’s from the vomiting, that dehydration may occur. (7)
Symptoms of dehydration
There are many symptoms of dehydration. Symptoms include:
- Thirst (obviosuly)
- Stronger urine
- Light headedness
- Dry mouth
- Urinating less than 4 times per day or infrequently
(For more information, check the link on there NHS website)
Likelyhood of becoming dehydrated
The risk of dehydration, depends on the who the person is.
The risk of dehydration differs depending on which population you belong to. These populations are:
- Healthy adults
In all honesty, for healthy functioning adults, the likelihood of becoming properly dehydrated isn’t likely. As long as you have access to clean water, you’ll most likely be fine. (8)
Drinking coffee will not dehydrate you.
The body likes homesostasis. This means the body likes to keep itself at a steady state. Thus is you lose more water, from the mechanisms listed above, you’ll most likely subscoviusly drink more to compensate.
Similar to how people subconsciously move less if they eat less.
Children are more likely to suffer from vomiting and Diarrhoea, thus they are more likely to become dehydrated than adults. (9)
Children being smaller also have larger surface area. This is a fancy way of saying they will lose more fluid, when they become ill. (10)
Finally, this may seem obvious. But not all children are capable of pouring themselves a glass of water. Also unfortunately it’s still prevalent in schools that teachers wont allow children to drink water in their lessons.
Though you are unlikely to become dehydrated, their is an increased of those in the elderly population becoming dehydrated.
Dehydration affects 20% to 30% of older adults(Miller, 2015)
Though most adults run a small risk of dehydration, the same isn’t for the elderly.
The difference with a lot of the elderly is that they are not as capable of just getting up and getting a drink. This means they need to rely on others for liquid. This means they could be forgotten about and left too long without liquid. (11)
Why do people think coffee will dehydrate you?
Caffeine is a diuretic. This is a fancy way of saying it makes you urinate more often. (12)
Because of this, it’s sensible to assume if you drink coffee, which has lots of caffeine, coffee will dehydrate you.
But, there is one big reason why this has been shown not to be the case.
Though you may lose liquid through urine. Dont forget you are also gaining liquid through drinking water. Coffee is mostly water.
Why is coffee a diuretic?
When you drink water and your bladder fills up. it’s thought this sends a signal to your brain to allow your bladder to release the liquid inside you. (13)
it is shown higher amounts of caffeine, causes people to urinate more. (14)
In some animal studies they noticed caffeine had an effect on their bladders. It increased the number of contractions there bladder had. This increase was compared to no caffeine. (15)
Yet another study showed, that some peoples urge to urinate on the coffee they drunk was very individual.
Why coffee does not cause dehydration
A study done in 2016, compared a load of drinks to water. The comparison was to find out which was most hydrating. The coffee wasn’t too far off from the water. (16)
Why is coffee hydrating?
Water obviously. The ratio of coffee to water is 99:1 or something close like that. (17)
When you drink coffee you’re drinking mostly water with a little bit of coffee bean residue. Unless you’re one of those people that has it loaded with cream, sugar, pumpkin and sprinkles. If that’s the case, you don’t like coffee, you like coffee-flavoured milkshakes.
Anyway, back to the point.
A study in 2014 investigated whether coffee causes dehydration.
52 guys who were habitual coffee drinkers were involved in this study. The study said these guys drank around 2-6 cups per day.
In this study they had to drink 4x200ml of coffee for 3 consecutive days. The coffee contained 4mg of caffeine per kg of their bodyweight. On a different 3 day they drank 4x200ml of what I assume was decaf coffee.
In this study bodyweight and body water was measured.
What they found there was no major differences in bodyweight or water, whether the drank caffeine or not.
Considering they were drinking what is a large amount of caffeine, this study would add to the body of evidence that coffee does not cause dehydration. (18)
Does coffee count towards daily fluid intake?
Yes, it indeed does.
The NHS eatwell guide has included it as one of your fluids you can drink. (19)
This is what the ‘British Nutrition Foundation’ say about drinking coffee to get your fluid intake up:
“Tea or coffee can also count towards your fluid intake. Although the caffeine found in tea and coffee can make you produce more urine, consuming moderate amounts does not appear to affect hydration” (19)British Nutrition Foundation
My only word of caution is; if you drink coffee regularly, like me, it really is better to go without the sugar.
Not because sugar is “bad”, but it does add a lot of calories, which will not fill you up. Your teeth would also benefit too. (20)
Instead either do what I did and drink good quality coffee which doesn’t need sugar to disguise the bad taste. Or use sweetener instead. I promise you sweeteners are safe, despite what the non-evidence-based websites say.
Reason not to drink too much coffee
Yes coffee does count towards your daily fluid intake. But still, I wouldn’t recommend that you only drink coffee. Though coffee is good for you and is hydrating, the caffeine content can still have side effects if you have too much.
Side effects include:
- Poor sleep
- Higher blood pressure
Caffeine has a half life of 5-7 hours. This means if you drink 400mg of caffeine, it will take that much time to excreted 200mg of coffee out of your system.
Thus if you drink a lot of coffee in the evening, theres a chance your sleep will be disrupted.
This happens because caffeine blocks what are known as adenosine receptors. These receptors are what helps us to sleep. Thus when you have too much caffeine in your system, you’ll struggle to sleep.
A lack of sleep can cause issues such as weight gain (increase in huger, so you eat more), poorer decision making and a poorer attention span.
So if you drink coffee, make sure to keep it around 5-7 hours before you sleep at least. (22)
High blood pressure
High blood pressure is not something you want. High blood pressure leads to an increase risk of heart diseas, one of the greatest causes of death on the planet.
There isn’t a concrete answer as to why. Mainly theories.
One theory being that it inhibits, which signals to the arteries to widen. This means blood pressure would increase, due to the more narrow pathway it will have to follow.
The other theory is, that the increase in caffeine will produce more adrenaline, which raises blood pressure.
Either way papers have shown caffeine is directly linked to an increase in blood pressure. (23)
Either way caffeine is linked to high blood pressure, hence why youre advised not to drink coffee before doing a blood pressure reading.
Though the research is still young. There are a few studies currently suggesting those that drink more coffee, will exert higher levels of anxiety.
A study done in 2021 observed this very finding. (24)
Coffee drinker and non coffee drinkers were split into groups.
The coffee drinkers were shown to have more stress than the non coffee drinkers. It was also shown that drinking more coffee was correlated with higher stress for the males in the study/
How much coffee is safe?
For the average adult, you want to keep your intake of caffeine to under 400mg per day. (25) Keep it under that and you should be all good.
On average that is 4 cups of coffee per day. Yes, I know caffeine content varies and cups come in different shapes and sizes. But just practice common sense and you’ll be fine.
If you’re a larger person you’ll be fine drinking that amount. If you’re a smaller person, you’d most likely want to lower that amount a little.
One last thing on caffeine. I’m not sure if it’s just a British thing, but I know of a lot of adults that drink coffee in the evening or at night. It’s not my place to tell you to never do that. But I’d really advise against it if you can.
For most people, it’ll really disrupt your sleep. It’s definitely something you want to stick with, in the morning. That then gives your body enough time to have it out of your system by the time you go to sleep. Ideally, you want to stop drinking coffee 6 hours before you sleep. (26)
Some people are lucky and don’t get affected, but most are not.
If you want to drink coffee later in the day, I’d advise you to change to decaf for the evening. It does contain trace amounts of caffeine but far far less than the real version. It contains around 7mg per cup, which is still a lot less than 100mg per cup.
Though coffee may not dehydrate you, it doesn’t mean it should be your only drink choice.
How much fluid do I need to drink per day?
The UK government recommends 6-8 cups or glasses per day. In theory this means you could get half your intake from coffee everyday.
For most people 6-8 glasses a day does the job, hence why it’s recommended.
However if you wanted to be that bit more individualised. It’s said to check the colour of your pee. If it’s completely colourless, that means you’re probably drinking too much. And if it’s too strong a yellow then you could probably drink more. You want a nice clear yellow colour, then you know you’re all good. (27)
If I’m being honest. Most people are good at regulating their hydration. The body seems to know when you’re thirsty or not.
But there is nowhere on the Uk official nutrition website or NHS where it says coffee will dehydrate you.
So, does coffee dehydrate you?
No it does not, coffee does not dehydrate you. In-fact quite the opposite, it actually hydrates you.
If you are sensible, you can enjoy a few cups of coffee in the morning, whilst still getting the hydration benefits.
Yte, it may not dehydrate you, but this doesn’t mean you want to go crazy.
Too much caffeine, can still lead to a risk increase in high blood pressure, dependence, poor sleep and anxiety.
the bottom line is enjoy your coffee, but be sensible and stick with the government guidelines.
Josh is a Registered Associate Nutritionist, with the Association for Nutrition (AFN). He completed his degree in Nutrition at the University of Roehampton in 2021. He passed with a First Class with Honours.
Josh is also a tutor for up-and-coming Personal Trainers, where he teaches a Level 4 Advanced Nutrition course. This is for Personal Trainers looking to upskill their nutrition knowledge. This is done at Norfolk Health & Fitness.