Debunking The 3 Biggest Coffee Myths
Coffee helps us tackle the day, but the little helper also has its downsides. Can coffee cause dehydration, do we get used to caffeine and what about that famous afternoon crash?
Text by: Katalin Wagner, M.Sc., Physical scientist | DocCheck Team
Busy day? Enjoy thetl;dr at the end of the page!
Caffeine is one of the most commonly used lifestyle drugs of our time. Whether by drinking tea and coffee or taking caffeine supplements — this little molecule can keep us awake during night shifts, or final exams. But have you heard about the dehydrating effect of caffeine, or how early coffee consumption makes us tired during the day? There are as many myths about caffeine as there are types of tea and coffee. Is there any truth to that or can we continue to enjoy our morning cup of joe? A group of researchers from the US have dug deep into the pool of available studies on caffeine and have summarized their findings in a review.
But first things first: How does caffeine even work? Throughout the day, our bodies use adenosine triphosphate (ATP) as fuel. One of its breakdown products is adenosine, which then accumulates in the neurons of the brain. These adenosine molecules bind to free adenosine receptors of the neurons, signaling to the brain that it has been very active and it’s time for a break — we get sleepy. Caffeine (1,3,7 — trimethylxanthine) interferes with this signaling by competitively binding to adenosine receptors and thus promotes arousal.
Dehydrated Caffeine-Lovers
One of the most common myths about caffeine is its diuretic effect. Previous research has suggested that caffeine at a dose of ≥ 300 mg or 3 mg/kg (equates to 2–3 cups of coffee) could have a diuresis-like effect. This dogma has since been challenged by more recent research. Assuming a caffeine intake of about 165–230 mg/day, which is about the average caffeine intake for Americans, researchers revealed the diuresis-like effect of caffeine to be unfounded, especially in habitual caffeine consumers. When sticking to the recommended limit of caffeine intake by the Food and Drug Administration (FDA) of ≤ 400 mg/day (4–5 cups of coffee) fluid loss should be of no concern. Only excessive doses of more than 500 mg might promote an increased urine output.
“To avoid diuresis when supplementing caffeine in a workout regime, sufficient hydration is indispensable — better be safe than sorry.“
But what about your sporty patients who already sweat more while training? Many athletes on professional and recreational levels supplement caffeine for a better focus and effect of their workout. When already sweating, additional fluid loss could have a negative effect on workout performance and well-being. However, not only the caffeine intake, but also individuals sweat rate, hydration during the workout, and genetics play a crucial role in the athletes’ state of hydration and fluid loss. Thus, it is difficult to determine if increased fluid loss is due to caffeine supplementation or individual constitution. Even the form of caffeine supplementation (pill or multi-ingredient pre-workout supplement) has a potential influence. To avoid diuresis when supplementing caffeine in a workout regime, sufficient hydration is indispensable — better be safe than sorry.
Better Not Get Used To It
Even though coffee is an acquired taste, caffeine is consumed by almost everyone — in the shape of Cola, Energy drinks, or other caffeinated fizzy drinks. Research has shown that habitual caffeine intake causes an up-regulation of adenosine receptors which could dampen the effect of caffeine on the consumer. However so far this has only been shown in rats and the question remains: Can we acquire a higher caffeine tolerance, and will it affect acute caffeine supplementation effects?
Caffeine consumption in habitual consumers differs from individual to individual. Thus, investigating the habitual effect is a challenging task. Some studies have investigated the effect of acute caffeine supplementation on athletic performance in habitual caffeine consumers. However, according to the authors of the review, there is a huge lack of consistency in results. There is some evidence pointing towards a habituation effect and that a higher single dosage (6–9 mg/kg rather than 3 mg/kg) is required to affect performance in habitual caffeine consumers. Yet, more research is needed to say for certain which levels of daily caffeine consumption could dampen the effect of acute supplementation.
Coffee And The Afternoon Crash
Another day another advice from Dr. TikTok: Delay your morning coffee by up to two hours and you will avoid the “afternoon crash”. Hereby referring to the dip in energy and increased sleepiness in the afternoon. The rationale for this is that caffeine interferes with the secretion of cortisol and prolongs the waking peak because adenosine levels are still declining after waking. Moreover, there is an alleged afternoon crash when caffeine is eliminated from the system. But is there any truth to that?
Cortisol levels are highest approximately one hour after waking and decline throughout the day. The consumption of caffeine however can elevate the cortisol levels significantly (around 30 % higher compared to control groups). As the authors make clear: this increase in cortisol levels will happen no matter at what time the coffee is consumed, delaying the morning coffee will not reduce this effect. In habitual caffeine consumers, the effect of caffeine on cortisol levels might be dampened or even eradicated in individuals with high caffeine intakes (300–600 mg/day). Moreover, the authors state that according to available literature, the normal diurnal pattern of cortisol is not altered by caffeine consumption.
“There is no scientific evidence to support an afternoon crash!”
The assumption that caffeine interferes with the decline of adenosine after waking is also incorrect. In fact, adenosine buildup begins immediately upon waking and continues gradually throughout the day. Thus, it is not caffeine but merely the fact of being awake that increases adenosine buildup after waking. There is no scientific evidence to support an “afternoon crash” caused by the consumption of coffee in the early morning.
To Coffee Or Not To Coffee?
The bottom line is that any form of over-consumption of caffeine can have potential negative effects. Whether these might be dehydration, a dampened effect of acute supplementation, or nervousness. Patients who are at increased risk of experiencing negative effects and chronically high consumers should consider reducing their daily intake. The daily dose of caffeine should not exceed 300 mg/day or 3 mg/kg, as recommended by the FDA and European Food Safety Authority (EFSA). Moreover, you should recommend your patients to opt for natural sources of caffeine, such as coffee or tea as they additionally come with beneficial antioxidants and phenolic compounds.
tl;dr
Myth: Caffeine Causes Dehydration
Recent research disproves the belief that caffeine significantly increases fluid loss in habitual consumers. Following the FDA’s recommended limit of 400 mg/day should prevent any concerning diuretic effects, and individual hydration needs during exercise also play a crucial role.
Myth: Habitual Caffeine Consumption Requires Higher Doses for Effectiveness
Although some studies suggest that regular caffeine intake might lead to tolerance, requiring higher doses for the same effect, the evidence is inconsistent. More research is needed to determine the impact of daily caffeine consumption on the efficacy of acute supplementation.
Myth: Morning Coffee Leads to an Afternoon Energy Crash
There is no scientific basis for the idea that drinking coffee in the morning causes an afternoon crash. Caffeine consumption does not interfere with the normal decline of adenosine or cortisol patterns throughout the day, and the so-called “afternoon crash” is not supported by evidence.
Source:
Antonio, J. et al. Common questions and misconceptions about caffeine supplementation: what does the scientific evidence really show? Journal of the International Society of Sports Nutrition, 21(1). https://doi.org/10.1080/15502783.2024.2323919.
Image Source: Nathan Dumlao, unsplash
