Introduction
Water, as the principal constituent of the body, accounts for fifty to seventy percent of total body weight and is essential to our well-being. It is generally recommended that we consume about 1.5 to 2 litres of fluid per day.
Coffee and fluid intake
Consumers of coffee are frequently being wrongly advised to cut down on their consumption because the caffeine in coffee is a diuretic and drinking coffee will result in dehydration. This is out of date information and is simply not true! Recent research has shown that caffeine, as commonly consumed in coffee, is no more a diuretic than water (1 – 3) and concludes that ‘scientific evidence does not support the claim that caffeine containing beverages promote dehydration’.

A diuretic is defined as any substance that increases the production of urine – put simply this means anything that makes you want to pass water.

Although caffeine does have a mild diuretic effect, it is not true to say that drinking caffeine-containing drinks in moderation will result in dehydration. Coffee, along with other popular hot and cold drinks, is accepted as being an important source of fluid in the diet when consumed in moderation. Contrary to popular advice you DO NOT need to drink more water to compensate for consuming caffeinated drinks (3).

Summary
The diuretic effects of caffeine, as consumed in a cup of coffee, can be considered weak to negligible and certainly no greater than the effects seen when drinking plain water. For people following calorie-controlled diets, black coffee or coffee with skimmed milk and no sugar contains virtually no calories at all, so can be an important source of fluid that will not affect weight gain. Moderate coffee consumption, of 4-5 cups per day, is perfectly safe for the general population, and may confer health benefits. Pregnant women should however moderate their intake following the guidelines issued by the Food Standards Agency, to 200mg caffeine per day from all sources.

References
1. Armstrong LE. International Journal of Sport Nutrition & Exercise Metabolism, Volume 12, 2002
2. Armstrong LE. International Journal of Sport Nutrition & Exercise Metabolism, Volume 14, 2005
3. Armstrong LE. Exercise and Sports Science Reviews, Volume 35, 2007
4. British Nutrition Foundation – www.nutrition.org.uk