Coffee is often wrongly thought of as causing dehydration but in fact, research shows that coffee can actually help us stay hydrated by contributing to our daily fluid intake 1,2,3. It is a common misconception that because caffeine is a mild diuretic, it causes dehydration.
This is thought to stem from a 1997 study which reported a significant increase in volume of urine excreted in individuals drinking coffee, compared with those drinking an equivalent amount of water.
However, the subjects in this study had abstained from consuming any caffeine for five days prior to the treatment, effectively making them ‘caffeine-naïve’ – and increased urine excretion in these circumstances is a well-documented effect 4.
Latest findings show that in fact caffeine, at levels consumed throughout the day in a couple of cups of coffee, is no more a diuretic than plain water.1
The British Dietetic Association and other UK expert bodies such as the British Nutrition Foundation are in agreement that moderate coffee consumption (up to four to five cups per day) can contribute to your daily fluid intake and will help to keep you alert and hydrated 1,2,3.
Similarly, proceedings from a conference in North America advise consumers that drinking a variety of caffeinated beverages, including coffee, can contribute to meeting the body’s requirement for fluids – not surprising when you consider that black coffee contains more than 95% water 5.
This advice is reflected by the British Nutrition Foundation, which recognises milk, fruit juice, tea and coffee as important fluid sources 6.
“Many people still wrongly believe that hot drinks, and particularly coffee, are not good for us in the heat because they are dehydrating. However, there is a big difference between feeling that a drink is not as refreshing as you would like it to be and actually causing dehydration,” highlights Dr Sarah Schenker.
“When one cup of coffee is drunk, the body will retain all or most of the fluid, depending on current hydration status. Caffeine will exert a diuretic effect to varying degrees depending on dosage and caffeine tolerance of the person ingesting it.”3
As well as contributing to hydration, caffeine has also been shown to help sustain both alertness and concentration 7,8 and improve performance in a variety of tasks.
Drinking a cup of coffee about 20-30 minutes before exercise can allow you to exercise for up to 30% longer 8.
The caffeine contained in a single cup of coffee can increase the amount of adrenaline produced by the body, which stimulates energy production and improves blood flow to the muscles and the heart 8.
As a result, caffeine can lead to improvements in performance and is most notable in endurance sports such as swimming, cycling and tennis 9.
For the majority of people, 400mg of caffeine per day is considered moderate consumption – this equates to around four to five cups of coffee.
This will depend on the size and strength of the serving and it’s important to remember that caffeine can be found in other foodstuffs, such as tea, cola and chocolate.
For pregnant women, the NHS recommends a safe upper limit of 200mg of caffeine per day from all sources – approximately two to three cups of coffee or equivalent.
References
1. Ganio, MS et al. Evidence-based approach to lingering hydration questions. Clinics in Sports Medicine, 26: 1-16, 2007.
2. British Dietetic Association, www.bda.uk.com.
3. British Nutrition Foundation, www.nutrition.org.uk.
4. Neuhauser-Berthold M et al. (1997). Coffee consumption and total body water homeostasis as measured by fluid balance and bioelectrical impedance analysis. Ann Nutr Metab 41, 29-36, 1997.
5. Kolasa KM et al. (2009). Hydration and health promotion. Nutr Today 44, 190-203.
6. British Nutrition Foundation, www.foodafactoflife.org.uk/attachments/b5784ad9-550d-41fee2e7a4dd.pdf, last accessed July 2013.
7. Brunyé TT, et al (2010). Acute caffeine consumption enhances the executive control of visual attention in habitual consumers. Brain Cogn;74:186-92.
8. Ruxton, C.H.S. The impact of caffeine on mood, cognitive function, performance and hydration: a review of benefits and risks, British Nutrition Foundation Nutrition Bulletin, Volume 33, 2008.
9. Macintosh BR and Wright BM, Canadian Journal of Applied Physiology. 1995;20:168-17.
Source: The British Coffee Association
