Coffee & Hydration: Does Coffee Consumption Lead To Dehydration?
“Coffee dehydrates you”
“For every coffee you consume, have a glass of water with it”
Above are typical statements that come to mind when people discuss coffee and hydration. Recent figures suggest that around 2 billion cups of coffee are consumed globally each day, with the UK accounting for 55 million. With such widespread daily coffee consumption are such statements regarding dehydration of concern for the regular coffee consumer, or should such statements be shelved with other nutrition myths?
First, let us familiarise ourselves with commonly available sources of caffeine:
Caffeine and Hydration
Concerns regarding caffeine and dehydration are based upon the diuretic potential of caffeine (a methylxanthine). This has led to the belief that fluid balance is compromised by caffeine consumption. However, before stating that all caffeine consumption negatively influences fluid balance it is important that we take a deeper look at the scientific research, especially the methodologies utilised.
When reviewing the scientific literature concerning the effect of caffeine consumption upon hydration status a variety of different methods have been utilised, which makes it challenging to compare the findings of such research. One important consideration is that the majority of research has primarily been conducted with participants consuming caffeine in supplemental form (tablet or powder) as anhydrous caffeine (pure caffeine). However, it is important when discussing both caffeine and coffee to make the distinction between the two. Coffee is considered a unique source of caffeine, in comparison to pure caffeine, due to the additional presence of bioactive compounds (e.g. chlorogenic acids). Therefore, coffee should not be considered the same as pure caffeine sources due to the potential interaction of bioactive compounds.
Further methodological differences between previous research include the variety in total caffeine dose consumed, study duration, hydration markers measured, incorporation of a caffeine withdrawal period prior to the study, the selection of caffeine naïve (non-typical caffeine consumers) or caffeine habituated participants (typical caffeine consumers), gender and the use of absolute doses (instead of relative to an individuals body mass) and the additional of pure caffeine to decaffeinated coffee.
Coffee and Hydration
Acknowledging the limitations of previous research, one study set out to address whether moderate coffee consumption amongst regular coffee consumers could contribute to daily fluid intake, or whether such consumption has a negative effect upon hydration status. Over 4 days male regular coffee consumers were provided either 4 mugs (200ml) of coffee (containing 4mg per kg of body mass caffeine) or 4 mugs of water (200ml) per day. Both conditions were fluid matched, with further researcher instruction upon controlling dietary intake and other fluid consumption. Regarding hydration assessment, body mass, total body water and urine and blood analysis were conducted. A particular strength of this study is the utilisation doubly labelled water (DLW), which is considered the gold standard method for total body body water estimation highlighting fluctuation over time.
What Did They Find?
“No significant difference in the hydrating properties of coffee or water across a wide range of hydration assessment indices/haematological (blood) markers.”
This led the authors to conclude “these data suggest that coffee, when consumed in moderation by caffeine habituated males contributes to daily fluid requirement and does not pose a detrimental effect to fluid balance.”
The above study suggests that moderate consumption of coffee amongst regular coffee consuming males can contribute to daily fluid intake without a negative effect upon hydration. Previous research had put forward a potential absolute daily caffeine threshold of around 300mg over which caffeine consumption would have a negative effect upon hydration. Although, the average total daily caffeine consumption within the infographic study was similar (308mg), the range of total caffeine consumption amongst participants varied (204-453mg) due to the methodology basing caffeine consumption relative to individual body mass (those that weigh less at the lower end of caffeine intake and heavier individuals at the higher end).
It is also important to acknowledge the potential limitations of the above research. In particular, questions regarding whether such findings are applicable to females or the non-regular caffeine consumer remain. Interestingly, a study amongst low caffeine consumers (<100mg/day) found no changes in total body water estimations via DLW when consuming moderate caffeine amounts (5mg/kg) in comparison to placebo. However, caution should be utilised when extrapolating such findings to the effect of coffee consumption by non-regular consumers. Such findings are similar to that of a 2015 meta-analysis upon caffeine and hydration, with the authors concluding that the minor diuretic effect of caffeine does not lead to excessive fluid loss, although the diuretic potential was greater within females than males.
Coffee and Caffeine Content
The caffeine content within coffee can vary considerably depending upon numerous factors. For example, if we take 1 cup (8oz) of instant coffee this roughly provides on average 60mg of caffeine (range 12-169mg), whereas a brewed coffee roughly contains 80mg (range 40-110mg). Regarding espresso coffee, an average coffee provides around 106mg of caffeine per serve. Interestingly, from a sample of 97 coffees purchased from coffee shops located within 5 different Australian shopping centres the caffeine content of espresso coffee was found to show great variability with caffeine ranging 24-214mg. The below infographic highlights the difference in caffeine content of common coffee choices from popular UK coffee stores.
Why does the caffeine content of your coffee show such variability? Research suggests that espresso caffeine content is dependent upon two main factors:
(1) Industry Control
Coffee variety, bean preparation, amount of bean roasted and form of roasting.
(2) Extraction Variables Under The Control of The Technician
Water temperature, water pressure, grinding grade, amount of coffee ground and the amount of pressure (tamping) applied to coffee.
With such variance of coffee caffeine content between retailers, this leaves the question whether the caffeine content of the same beverages served from the same store vary? Previous research within the below infographic answered such a question highlighting that the caffeine content of the same choice of coffee may vary considerably from day to day.
It must not be overlooked that the overconsumption of caffeine can cause certain side effects such as jitters, headache, increased heart rate, performance impairment and diuresis. The timing of caffeine consumption should also be considered due it’s potential to impact upon sleep onset. Consumers, especially dieting individuals, should also be aware of the calorie content of some coffee drinks with additions (e.g. cream, syrup content, chocolate), which can soon add up if drunk frequently throughout the day or week.
- The moderate consumption of coffee containing 4mg of caffeine per kg of body mass amongst regular coffee consumers can contribute to daily fluid intake without negative impact upon hydration status.
- The caffeine content of coffee may vary due to numerous factors under both industry and coffee technician control.
- Individuals should be aware of calorie content of beverages, particularly those with numerous additions, if frequently consumed during the day or throughout the week.