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Athletes tend to be heavy coffee drinkers. But drinking coffee dehydrates you, right? If so, are the benefits of caffeine outweighed by the negative effects of the dehydration on your performance?
"}},"slug":"does-coffee-dehydrate-you","blogTags":"Hydration","featuredPost":false,"author":{"name":"Andy Blow","slug":"andy-blow","facebookHandle":"https://www.facebook.com/andy.blow.3","twitterHandle":"https://twitter.com/andybl0w?lang=en","instagramHandle":"https://www.instagram.com/andyblow","linkedInProfile":"https://uk.linkedin.com/in/andy-blow-47b90133","stravaProfile":"https://www.strava.com/athletes/6999012","bio":{"childMarkdownRemark":{"html":"Andy Blow is a Sports Scientist with a BSc Honours degree in Sports and Exercise Science from the University of Bath. An expert in hydration, he has co-authored a number of scientific studies and books.
\nHe was once the Team Sports Scientist for the Benetton and Renault Formula 1 teams and remains an adviser to the Porsche Human Performance Centre at Silverstone.
\nAndy has finished in the top 10 of IRONMAN and IRONMAN 70.3 races, as well as winning an XTERRA Age Group World title. It was his own struggles with cramp that led to him specialising in hydration and founding Precision Fuel & Hydration.
"}},"title":"PF&H Founder and Sports Scientist","headshot":{"file":{"url":"//images.ctfassets.net/428xzyjdw7rf/2LTns8O1ZGOHSfDQGv2jZz/f6470d62f0c1f14e7239432f60a0b765/Andy.png"}}},"scientificallyReviewed":null,"image":{"resize":{"src":"//images.ctfassets.net/428xzyjdw7rf/6FJ0ARTwxh3xSXq6NqJJyC/370af0fcfb49c3fd75c28c78fc2d4814/Does_coffee_actually_dehydrate_you.webp?w=1200&h=630&q=70&fit=fill","width":1200,"height":630}},"socialMediaImage":{"resize":{"src":"//images.ctfassets.net/428xzyjdw7rf/2agygS6DArzIh0CEvAaKBf/3244389109d2909230b231cdf399914d/resized-Does_coffee_dehydrate_you.webp?w=1200&h=630&fl=progressive&q=90&fm=jpg&fit=fill","width":1200,"height":630}},"body":{"childMarkdownRemark":{"excerpt":"The general consensus is that caffeine can boost performance, especially during longer bouts of endurance exercise, so athletes tend to be heavy coffee drinkers…","html":"The general consensus is that caffeine can boost performance, especially during longer bouts of endurance exercise, so athletes tend to be heavy coffee drinkers. But what effect does coffee have on your hydration status?
\nThe idea that caffeine can promote dehydration isn't new. A small but influential study back in 1928 saw participants pee out up to 50% more urine when they drank caffeinated water and coffee. Most of us have probably felt this effect.
\nAnd caffeine is still widely regarded as being a mild diuretic (a compound that causes your kidneys to produce more urine than they normally would).
\n
A recent study looked at urine volumes produced in the 2 hours after drinking a range of drinks; the fluid loss from coffee was highest.
\nBut, the key thing that’s often not talked about is that the diuresis that coffee consumption can induce doesn't appear to result in a net fluid loss over a longer period, when you take into account the fluid that's absorbed and retained from the coffee itself.
\nThis has been relatively widely researched, with many studies coming to the conclusion that, although urine output can be increased with coffee/caffeine consumption, the actual result on body fluid balance doesn't appear to be negative overall.
\nThis has led to there being a gradual U-turn in the scientific community on the idea that drinking coffee will compromise your hydration status on a day-to-day basis.
\nThe diuretic effects on regular coffee drinkers seem to be way less pronounced than on those who have it infrequently and avoiding coffee for as little as 4 days can reverse the adaptations that reduce that diuresis markedly.
\nPeople handle caffeine differently, there are different genotypes that determine your body’s ability to metabolise caffeine.
\nSo it's not a stretch to think that this might mean the effects of caffeine might vary depending on your genetic make up. We probably all know people who seem to be able to drink coffee and tea all day long and show no signs of dehydration and others who just don’t seem to get on with it at all.
\nFor me, it’s highly likely that drinking coffee does not cause serious dehydration.
\nWith that said, I believe that in situations where maintaining a good hydration status is challenging (e.g. when training or travelling on long haul flight, etc), coffee is not the optimal choice for staying hydrated, especially if you don’t drink it regularly.
\nI also think that a level of personal experimentation and common sense needs to be employed to figure out what level of coffee consumption works well for you as an individual, as clearly it isn’t the same for everyone.
\nWorried about dehydration when you're training / racing?
\nTake our free Fuel & Hydration Planner to get personalised hydration strategy for your next race...
\nTake the Fuel & Hydration Planner
\nProfessor Raj Jutley is a consultant heart surgeon who co-founded Precision Fuel & Hydration with Andy Blow. He trained in Scotland and worked as a consultant in Nottingham, UK.
\nHe now spends the bulk of his time in Nairobi where he's worked as the Director of Cardiac Surgery at the Aga Khan University Hospital and he's currently setting up affordable healthcare systems in Kenya.
\nIn the UK, Raj was the medical consultant to the Porsche Human Performance Centre, as well as to the highly successful Racing Steps Foundation (www.racingsteps.co.uk).
\nRaj - who drives classic rally cars and won the South African National Championship Classic Class in 2019 - continues to be involved in a scientific capacity with Precision Fuel & Hydration and provides valuable input, specifically in response to medical-based queries.
\nProfessor Raj Jutley earned the following qualifications during his time in Scotland:
\nQualifications: BMedSci (Hon), MB ChB, DM, FCS ECSA, FRCS Eng, FRCS CTh\nEducational Bios:
\n- Pan Africa Heart Foundation Bio
\n- The Open Science Research Network Bio
Raj has over 40 peer-reviewed scientific articles to his name, with the aim to add more on the topic of customised hydration, and you can find examples of his published work below:
\nBooks
\nPublications
\nNormative data on regional sweat sodium concentrations of professional male team sport athletes (Journal of the International Society of Sports Nutrition)
\nPhD Supervision
\nPhD Thesis: The effect of individualised electrolyte supplementation on physical and cognitive performance in elite motorsport drivers (Justin Holland, University of Queensland, Australia, 2019)
\nPresentations/Abstracts
\n