Coffee can be an important source of fluid in the diet. Through careful experiments that passed peer review, Grandjean et al (1) have shown that caffeinated drinks should count towards the daily fluid intake in the vast majority of people.
For some medical conditions – such as kidney stones – patients are routinely advised to increase their fluid intake. However there is sometimes concern that drinks containing caffeine – while improving fluid intake may have a diuretic effect.
In two studies Curhan et al (2,3) found that greater intakes of regular and decaffeinated coffee, tea, beer and wine were associated with a decreased risk of stone formation, whereas greater intakes of apple and grapefruit juices were related to increased risk.
The diuretic effects caused by caffeine are weak to negligible under normal caffeine consumption and for people without urinary tract problems. Indeed one researcher claims that caffeine consumption’s diuretic effect is very similar to that of water (4). However, it is difficult to measure the effects, even in a laboratory situation.
A study by Nussberger et al (5) does not show a significant increase of urine excretion when comparing intake of drinks containing caffeine with water. And in a recent study attempting to classify alcohol and caffeine as diuretic substances (6), the author admits that there are no estimates of the chronic effect of caffeine on diuresis under variable free-living conditions.
A recent review of the available literature on caffeine ingestion and fluid balance conducted by R.J. Maughan and J. Griffin (7) using the Medline database, found that amounts of caffeine equivalent to that normally found in standard servings of coffee have no diuretic action.
Caffeine is a mild diuretic, and although it may slightly increase frequency of urination it does not increase the volume of urine excreted. It is true to say that single doses of caffeine (at least 250-300mg) have a diuretic effect, but doses at the levels commonly consumed in coffee have little or no effect. Indeed regular caffeine consumers become used to the effect, reducing any action even more.
Fluid Balance References
- Grandjean A.C. et al, Journal of the American College of Nutrition, 19, 591-600, 2000
- Curhan G.C et al, American Journal of Epidemiology, 143, 240-247, 1996
- Curhan G.C et al, Annals of Internal Medicine, 128, 534-540, 1998
- Armstrong L.E. International Journal of Sport Nutrition and Exercise Metabolism, 12, 189-206, 2002
- Nussberger J et al. Journal of cardiovascular Pharmacology, 15, 685-691, 1990
- Stookey J.D. European Journal of Epidemiology, 15, 181-188, 1999
- Maughan R.J. & Griffin J. J Hum Nutr Dietet, 16, 411-420, 2003