Is Coffee Dehydrating You?
A look at coffee consumption and it's effects on hydration status
Summary Bullet Points
Coffee contains caffeine which is thought to be a mild diuretic
The diuretic effects of caffeine only occur at relatively high doses (>250mg); however, these effects diminish as an individual builds tolerance to caffeine and becomes a habitual consumer
Coffee has been shown to provide similar hydrating effects to water when consumed by caffeine habituated individuals
Coffee doesn’t appear to cause dehydration and may even provide a number of health benefits when consumed regularly
Coffee is one of the most popular beverages in the world, second only to tea in non-water beverage consumption (1). It’s tasty, energizing, and an important part of our morning ritual.
Globally, we consume about 145 million bags of coffee per year- equating to almost 10 million tons (1). According to the Harvard T.H. Chan School of Public Health, over 60% of Americans drink coffee every day.
Given its widespread consumption and popularity, it’s important to consider the possible effects that coffee may have on our health when consumed regularly.
One of the most commonly expressed concerns surrounding that of coffee drinking is the effect that it has on hydration status, with a frequently held notion that it promotes dehydration.
In this newsletter we’ll examine this claim and take a look at what the science says.
What's in a cup of coffee?
Coffee beans- the hard black or brownish colored beans used to make coffee- are in fact seeds, which are derived from the fruit of the coffee tree. Once ripe, coffee berries are picked, the seeds are removed, processed, and dried, forming what is called a green coffee bean.
The green coffee bean is roasted at varying temperatures, ground, and combined with hot water. During the brewing process the water extracts various compounds from the grounds, forming the dark colored, acidic, and slightly bitter drink that we call coffee.
The average cup of coffee is about 98% water and 2% soluble plant matter. Although it comprises a relatively small fraction of coffee, the extracted plant matter contains a wide range of different molecules. In fact, there have been over 1,000 different bioactive compounds identified in a cup of brewed coffee (2).
Among these compounds is the world’s most widely consumed psychoactive drug and central nervous system stimulant; caffeine.
Coincidentally, caffeine is also classified as a diuretic, a substance that causes the production of urine and the excretion of water from the body.
Given this piece of information, along with the personal experience that many of us have with drinking coffee and making frequent trips to the bathroom, its logical to hypothesize that drinking coffee causes urine production and dehydration.
However, the relationship between caffeine, coffee drinking, and dehydration may be a bit more nuanced than it appears at first glance.
Caffeine as a Diuretic
Although caffeine does exert a small diuretic effect, it only appears to increase urine volume to a significant extent when consumed in rather large doses, above 250-300mg, the equivalent of about 3-4 cups of coffee (4). Some studies don’t observe diuretic effects until a dose of almost 400mg is provided (3).
Additionally, these effects are only observed in individuals who are not consuming caffeine on a regular basis. With the habitual ingestion of caffeine, the body builds a tolerance to its diuretic effects, in which case, even larger doses have a diminished effect (4).
Based on the evidence, caffeine is definitely a diuretic, however, it’s a fairly inefficient one and its effects are largely dependent on the dose and tolerance of the individual consuming it.
The amount of caffeine found in a typical serving of coffee, tea, or soda is relatively small, only about 80-100mg. This dose doesn’t appear to have a diuretic action at all, even in non-caffeine habituated individuals.
Larger doses, in excess of 250mg, may have slight diuretic effects on those who are not acquainted to such intakes. However, after achieving caffeine tolerance, which can occur in as little as 1-4 days, these higher intakes don’t seem to effect urine production either (5).
Coffee and Hydration Status
We must also consider the form in which caffeine is consumed.
Typically, caffeine is not consumed in isolation as a dry pill or powder. Rather, it’s ingested along with fluids, usually in the form coffee, tea, energy drinks, or sodas, all of which are about 98-99% water.
Dehydration occurs when the body slips into a negative fluid balance, a state where more water is lost from the body than is taken in. Given this definition, in order for coffee to promote dehydration, it must result in a net loss of more water from the body than is contained in the beverage itself.
Even though you may be consuming a mild diuretic, you’re consuming fluids along with it, helping to off-set any possible diuretic effect that may be present. Given the ineffectiveness of caffeine as a diuretic, as discussed earlier, it’s reasonable to hypothesize that coffee may actually be net hydrating and not dehydrating.
Several studies have directly tested the effects of coffee consumption on hydration status.
One study comparing the effects of coffee consumption to water ingestion in 50 male coffee drinkers found no differences in hydration status after three consecutive days of consuming equal volumes of either water or coffee. They concluded that coffee provides similar hydrating effects to water when consumed by caffeine habituated individuals (6).
Another study looking at a range of different caffeinated beverages, including coffee, soda, energy drinks, and tea concluded that there were, “no significant differences in the effect of various combinations of beverages on hydration status of healthy adult males. Advising people to disregard caffeinated beverages as part of the daily fluid intake is not substantiated by the results of this study” (7).
Finally, a 2003 review paper (4) examining caffeine and fluid balance studies from 1966-2002 concluded that, “studies offer no support for the suggestion that consumption of caffeine‐containing beverages as part of a normal lifestyle leads to fluid loss in excess of the volume ingested or is associated with poor hydration status”
Why does coffee make you pee?
The body fights to maintain a strict fluid balance, where ‘water in’ equals ‘water out’. When excess fluids are provided, the body gets rid of them as urine.
If you’re already in a well hydrated state, the addition of extra fluids leads to urine production. This is like pouring water into a bucket that is already full. The excess is not needed and it simply spills over.
Thus, consuming coffee when you’re already in a hydrated state, which is 98% water, will result in water excretion, especially if you’re a caffeine habituated individual and immune to the diuretic effects caffeine.
Coffee does not appear to be dehydrating when consumed by caffeine tolerant individuals. In fact, it seems to provide a very similar hydrating effect as water. Therefore, there is no clear reason to avoid coffee consumption in situations where fluid balance may be compromised.
For most of us consuming coffee on a regular basis, it may be an important beverage in helping us to stay hydrated. Additionally, in many countries, including the United States, coffee is the number one source of antioxidants in the diet (8,9). In general, the research demonstrates that moderate coffee consumption is not only be safe for most individuals but it may even provide a number of health benefits.
A 2017 review paper examining over 200 independent studies on coffee consumption and health outcomes found that moderate consumption, between 3-4 cups per day, was associated with a decreased risk for mortality, liver disease, cardiovascular disease, type 2 diabetes, Alzheimer’s, Parkinson’s, and cancer (10).
International Coffee Organization. Current State of Global Coffee trade. CoffeeTradeStats.2017. http://www.ico.org/monthly_coffee_trade_stats.asp
Jeszka-Skowron, M., Zgoła-Grześkowiak, A., & Grześkowiak, T. (2015). Analytical methods applied for the characterization and the determination of bioactive compounds in coffee. European Food Research and Technology, 240(1), 19-31.
Passmore, A. P., Kondowe, G. B., & Johnston, G. D. (1987). Renal and cardiovascular effects of caffeine: a dose–response study. Clinical Science, 72(6), 749-756.
Maughan, R. J., & Griffin, J. (2003). Caffeine ingestion and fluid balance: a review. Journal of human nutrition and dietetics, 16(6), 411-420.
Robertson, D. A. V. I. D., Wade, D. A. W. N., Workman, R. O. B. E. R. T., Woosley, R. L., & Oates, J. A. (1981). Tolerance to the humoral and hemodynamic effects of caffeine in man. The Journal of clinical investigation, 67(4), 1111-1117.
Killer, S. C., Blannin, A. K., & Jeukendrup, A. E. (2014). No evidence of dehydration with moderate daily coffee intake: a counterbalanced cross-over study in a free-living population. PLoS One, 9(1), e84154.
Grandjean, A. C., Reimers, K. J., Bannick, K. E., & Haven, M. C. (2000). The effect of caffeinated, non-caffeinated, caloric and non-caloric beverages on hydration. Journal of the American College of Nutrition, 19(5), 591-600.
Svilaas, A., Sakhi, A. K., Andersen, L. F., Svilaas, T., Strom, E. C., Jacobs Jr, D. R., ... & Blomhoff, R. (2004). Intakes of antioxidants in coffee, wine, and vegetables are correlated with plasma carotenoids in humans. The Journal of nutrition, 134(3), 562-567.
Bae, J. H., Park, J. H., Im, S. S., & Song, D. K. (2014). Coffee and health. Integrative medicine research, 3(4), 189-191.
Poole, R., Kennedy, O. J., Roderick, P., Fallowfield, J. A., Hayes, P. C., & Parkes, J. (2017). Coffee consumption and health: umbrella review of meta-analyses of multiple health outcomes. bmj, 359, j5024.