How Much Caffeine Should You Drink a Day?
“The powers of a man’s mind are directly proportional to the quantity of coffee he drank.”
Sir James MacKintosh.
Caffeine is a commonly used stimulant used not only in day to day life but also as a performance-enhancing substance for certain sporting activities. Although it is a widely used and readily available substance, do users really know enough about it, in terms of the recommended daily amount, the effects it has on the body and the mechanisms behind its impact on some and not others? Fear not, as we’re here to spill the beans and give you the answers to all your caffeine questions so you can understand how much caffeine should you drink in a day.
Where is caffeine found?
Caffeine is naturally found in coffee beans, the leaves and seeds of the Camellia sinensis (tea plant) and cocoa beans. It can also be artificially manufactured in labs. Nowadays both tea and coffee are widely available sources of caffeine, but there is also a growing market for other caffeinated drinks such as fizzy drinks, energy drinks and pre-workout shots. Caffeinated beverages vary a great deal in the amount of caffeine they contain e.g the type of bean, harvest processing, storage, and extraction method (espresso, french press, filtered) will all affect the final caffeine content in your cup of coffee (1).
“Caffeine sensitivity can vary greatly from person to person, largely due to the activity of a specific enzyme in the liver: CYP1A2”
What is the recommended caffeine intake?
It is advised that up to 400 milligrams (mg) of caffeine a day appears to be safe for most healthy adults, although this amount is more in the region of 300mg for pregnant women.
What is the mechanism of action and effects of caffeine in the body?
Caffeine is absorbed through the GI tract (2) and moves through cellular membranes, both of which occur at a rapid rate (3). It is broken down by the liver and the resultant products are paraxanthine, theophylline, and theobromine (4). Elevated levels can be seen in the bloodstream within around 15-45 minutes from consumption and levels appear to peak one hour post-ingestion (1).
It causes alertness and can have mood-enhancing effects as it blocks adenosine receptors in the brain, which usually cause relaxation and sedation (5).
Why does caffeine affect people differently and can you have too much?
For some, one cup of coffee can cause jitters and a cup after 3 pm is a sure sign of a sleepless night, whereas others can curl up with a cup of tea at bedtime and drift off straight afterwards. Why and how can people respond so adversely to the same substance?
Caffeine sensitivity can vary greatly from person to person, largely due to the activity of a specific enzyme in the liver involved with the breakdown of caffeine, CYP1A2. The more active the enzyme, the less sensitive you will be to caffeine (6). Factors such as age, gender, genes and the use of oral contraception can impact one’s sensitivity.
The effect of caffeine can in part be influenced by your habitual caffeine consumption ie. if you rarely consume it, you will be more inclined to react to its effects and even a small amount may cause undesirable effects including sleep issues and jitteriness. On the flip side, consistently high consumption can also lead to tolerance to its effects for some. In instances like this, a short hiatus will usually do the trick to reverse this.
The half-life of caffeine, ie. the time it takes for your body to break down half of it is around 5 hours for healthy individuals. This may be worth considering if you have a heightened sensitivity to it.
Side effects such as headaches, irritability, insomnia and nervousness, could all be warning signs of over-consumption of caffeine.
Can caffeine improve sports performance?
Caffeine is an extensively researched substance with studies showing numerous potentially beneficial effects on performance.
Primarily, it has been shown to impact the central nervous system and the perception of fatigue, but associations have also been made with adrenaline stimulation, fat mobilization, and muscle contractility(7).
“Caffeine has been shown to improve the rate at which glycogen stores are replenished post-workout when consumed in combination with carbohydrates.”
The majority of benefits have been shown in sustained maximal endurance exercise and has been shown to be highly effective for time-trial performance. It has also been found to be advantageous for intermittent or interval type team sports of high intensity, as well as strength-power sports(8).
Caffeine has also been shown to improve the rate at which glycogen stores are replenished post-workout when consumed in combination with carbohydrates(9). This is particularly useful if your sessions are in close succession or you train intensely extremely frequently.
Is caffeine bad for you and should you avoid it?
In short, not in my opinion, if enjoyed responsibly. If you’re finding you’re relying on it to get through the day or experiencing some of the adverse effects discussed, however, it may be time to take a step back and assess when and why you’re reaching for a coffee and perhaps make some lifestyle changes instead.
If you can’t get through the morning without your usual fix, it may be worth assessing your sleep quality, duration and patterns. It may be as easy as working on your nighttime routine in order to maximise the chance of getting a restful night’s sleep, rather than reaching for a cuppa.
If you experience a mid-afternoon slump, it may be useful to consider your meal timings and composition as it could be caused by a dip in your blood sugar levels. Our bodies perform at their best when blood sugar levels are kept relatively constant. Therefore, consider having fibre-rich, complex carbohydrates as part of your lunchtime meal or an afternoon snack in order to combat these effects. Other factors such as consuming enough water and even getting up from your desk for a short walk should also be taken into consideration before reaching for a latte.
On the whole, caffeine certainly has its perks and can undoubtedly be enjoyed in moderation for most healthy adults.
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- Angeloni G, et al. What kind of coffee do you drink? An investigation on effects of eight different extraction methods. Food Res Int. (2019)
- McArdle WD, Katch FI, Katch VL. Energy, nutrition, & human performance. Baltimore Lippincott, Williams & Wilkins; 2007. Exercise physiology. (Series Editor)
- Fredholm BB, Battig K, Holmen J, Nehlig A, Zvartau EE. Actions of caffeine in the brain with special reference to factors that contribute to its widespread use. Pharmacol Rev. 1999;51:83–133.
- Graham TE, Spriet LL. Metabolic, catecholamine, and exercise performance responses to various doses of caffeine. J Appl Physiol. 1995;78:867–74. [PubMed]
- Childs E, de Wit H. Subjective, behavioral, and physiological effects of acute caffeine in light, nondependent caffeine users. Psychopharmacology (Berl). (2006).
- dePaula J, Farah A. Caffeine consumption through coffee: content in the beverage, metabolism, health benefits and risks. Beverages. 2019;5(37).
- Andrea Kench, Hiran Selvadurai, in Diet and Exercise in Cystic Fibrosis. The Sports Medicine Resource Manual, 2015, Pages 317-332
- Goldstein, E., Ziegenfuss, T., Kalman, D., Kreider, R., Campbell, B., Wilborn, C., Taylor, L., Willoughby, D., Stout, J., Graves, B., Wildman, R., Ivy, J., Spano, M., Smith, A. and Antonio, J., 2020. International Society Of Sports Nutrition Position Stand: Caffeine And Performance.
- Pedersen DJ, et al. High rates of muscle glycogen resynthesis after exhaustive exercise when carbohydrate is coingested with caffeine. J Appl Physiol (1985). (2008)
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