Caffeine & the Body: Effects, Benefits & Risks

Article by Vibhaavari Venkatesh

It’s 2am and your deadline is fast approaching. You’re already on your third cup of coffee. Sound familiar? What helps to keep you awake during those all-nighters and what gives you that sudden alertness on a tired Monday morning?

Caffeine is widely consumed through coffee and tea, but intake from soft drinks and energy drinks has surged in recent years. As the most commonly used and socially acceptable psychoactive substance, how much do we really know about its effects?

What is Caffeine? (Natural vs Synthetic Sources)

Caffeine is a central nervous system (brain + spinal cord) stimulant, which is also the most widely consumed ingredient worldwide with coffee being the second most commonly consumed beverage across the globe after water (Butt MS et al).

Caffeine is obtained both naturally, such as coffee beans, tea leaves, cocoa nuts, and Kola nuts, and synthetically, which are obtained from the laboratory in a concentrated form and can be found in various products such as energy drinks and soft drinks (Temple JL et al).

Benefits & Risks

The preparation process of coffee—such as using different beans, roasting methods, and brewing techniques—usually determines the caffeine content. Additionally, it can depend on the portion or serving size of the particular food or drink (Stavric B et al).

Caffeine can offer a range of benefits that make it a popular choice for many. Caffeine concentration in low (50-250 mg) to moderate (250-400 mg) dosages might increase alertness and attention, allowing you to stay productive and focused throughout the day. For athletes, caffeine may boost endurance and exercise performance, making it a perfect addition to training routines. Additionally, it can slightly increase metabolic rate for a short period of time. Beyond these benefits, caffeine—along with compounds like chlorogenic acids and trigonelline, which is majorly found in coffee and tea—may play a role in hepatoprotective effects, supporting liver health (de Paula J et al, Modi AA et al).

Anything in excess can become a problem, and caffeine is no exception. Overconsuming from 400 to 2000 mg caffeine/day potentially leads to restlessness, anxiety, irritability, and insomnia. It can also cause dehydration, increased heart rate (tachycardia), and gastrointestinal issues such as nausea, vomiting, and diarrhea, especially when taken on an empty stomach (de Paula J et al).

How caffeine affects certain groups of people:

Pregnancy

During pregnancy, caffeine may easily cross the placenta and enter the growing foetus. Unlike adults, a foetus lacks the essential enzymes to metabolise caffeine efficiently, leading to longer exposure of caffeine in both the mother's and the foetal blood, resulting in a slower rate of metabolism (Ricardo Rohweder, et. al ). According to current NHS guidelines, pregnant women should consume no more than 200 mg of caffeine per day (NHS England), which is equivalent to about two cups of instant coffee. Consistently exceeding this quantity may increase the likelihood of complications during pregnancy.

Breastfeeding

If you're a breastfeeding mom, you might want to keep an eye on your caffeine intake. As a natural stimulant, caffeine can pass through breast milk and potentially make your baby restless or fussy. While there isn’t a clear-cut limit on how much is too much, babies metabolise caffeine differently and may be more sensitive to its effects.

Some babies whose mothers consume high amounts of caffeine have shown signs of irritability, jitteriness, and disrupted sleep patterns. It’s not just coffee to watch out for—cola, tea, matcha and energy drinks also contain caffeine and can have similar effects. Additionally, drinking more than 450 ml of coffee per day has been linked to low iron levels in breast milk, which may contribute to mild iron deficiency anemia in some breastfed infants (Drugs and Lactation Database (LactMed®)

Children

Caffeine consumption among children and adolescents is increasing at an alarming rate, mainly through energy drinks and sodas, despite the lack of a known safe dosage for them. This trend is particularly alarming as these beverages are mostly marketed as performance boosters, influenced by social pressures, or advertised as an aid for sports. What’s even more concerning is that caffeine is now being added to various everyday products like gum, mints, and candy, making it more accessible to young consumers.

Childhood and adolescence are crucial for growth and brain development, requiring proper sleep and balanced nutrition for overall well-being. Caffeine can interfere with sleep quality, making it harder for children to get the rest they need to function properly. Additionally, many caffeine-containing beverages are high in sugar, contributing to the rise in tooth decay and childhood obesity. The combination of caffeine and sugar not only affects immediate health but can also increase the risk of long-term problems, such as unhealthy eating patterns (Temple JL et al).

Common Misconceptions

  1. Myth: Caffeine dehydrates you at rest.
    Fact: Moderate daily caffeine intake (< 3 mg/kg) does not substantially raise urine output in habitual users. Only very large doses (>6 mg/kg) may cause excessive urination.

  2. Myth: Pregnant women can safely consume caffeine.
    Fact:     The evidence supports that high caffeine consumption during pregnancy may be related to adverse consequences and should be limited.

  3. Myth: Caffeine causes heart problems, weakens bones, and promotes bone mineral loss.
    Fact: Moderate caffeine consumption (< 400 mg/day) is safe and not associated with heart problems. However, further research is needed on its possible effects on bone mineral density, particularly in females.

  4. Myth: Caffeine works the same for everyone.
    Fact: Individuals react differently to caffeine's effects.

  5. Myth: Delaying caffeine use after waking up may help to avoid an afternoon crash.
    Fact: Evidence suggests delaying caffeine intake in the morning might prevent an afternoon energy crash.

Understanding Caffeine Tolerance and How to Reset It

Frequent caffeine intake can create a tolerance, making individuals less responsive to its effects and potentially increasing their consumption over time. This happens because caffeine might block adenosine, a neurotransmitter that regulates sleep and alertness, prompting the body to produce more adenosine receptors. While tolerance varies, up to 400 mg of caffeine per day (about four cups of coffee) before 5pm (and not on an empty stomach!) is generally safe for healthy adults, except pregnant women. There are no specific guidelines for children or adolescents, but limiting intake is advised.

Quitting caffeine suddenly can cause withdrawal symptoms like headaches, fatigue, irritability, and trouble concentrating. Even small daily doses can trigger withdrawal. To reset your tolerance, gradually reducing your intake or switching to decaf may help. This allows your body to adjust while keeping caffeine effective when you consume it. See below for the amount of caffeine present in day-to-day consumed beverages. By managing intake mindfully, you can enjoy caffeine’s benefits without dependency (Rodak K et al, Sajadi-Ernazarova KR et al).

  • Brewed coffee 

    • Caffeine per 100 ml: 60–100 mg

    • Serving size: 150 ml

    • Caffeine per serving: 90–150 mg

  • Espresso

    • Caffeine per 100 ml: 100–150 mg

    • Serving size: 30 ml

    • Caffeine per serving: 30–50 mg

  • Instant Coffee

    • Caffeine per 100 ml: 27–72 mg

    • Serving size: 150 ml

    • Caffeine per serving: 40–108 mg

  • Decaffeinated Coffee

    • Caffeine per 100 ml: 1–3 mg

    • Serving size: 150 ml

    • Caffeine per serving: 2–5 mg

  • Tea

    • Caffeine per 100 ml: 6–22 mg

    • Serving size: 250 ml

    • Caffeine per serving: 15–55 mg

  • Iced Tea

    • Caffeine per 100 ml: 6–10 mg

    • Serving size: 250 ml

    • Caffeine per serving: 15–25 mg

  • Coca Cola

    • Caffeine per 100 ml: 10 mg

    • Serving size: 250 ml

    • Caffeine per serving: 25 mg

  • Diet Coke

    • Caffeine per 100 ml: 13 mg

    • Serving size: 250 ml

    • Caffeine per serving: 33 mg

  • Decaffeinated Coke

    • Caffeine per 100 ml: 0 mg

    • Serving size: 250 ml

    • Caffeine per serving: 0 mg

  • Energy Drinks (Monster)

    • Caffeine per 100 ml: 34 mg

    • Serving size: 250 ml

    • Caffeine per serving: 85 mg

  • Red Bull

    • Caffeine per 100 ml: 34 mg

    • Serving size: 250 ml

    • Caffeine per serving: 85 mg

  • Energy Shots (e.g., 5-Hour Energy)

    • Caffeine per 100 ml: 333 mg

    • Serving size: 60 ml

    • Caffeine per serving: 200 mg

  • Chocolate Milk Beverage

    • Caffeine per 100 ml: 1–3 mg

    • Serving size: 250 ml

    • Caffeine per serving: 2–7 mg

References

  1. .Butt MS, Sultan MT. Coffee and its consumption: benefits and risks. Crit Rev Food Sci Nutr. 2011 Apr;51(4):363-73. doi: 10.1080/10408390903586412. PMID: 21432699.

  2. Temple JL, Bernard C, Lipshultz SE, Czachor JD, Westphal JA, Mestre MA. The Safety of Ingested Caffeine: A Comprehensive Review. Front Psychiatry. 2017 May 26;8:80. doi: 10.3389/fpsyt.2017.00080. PMID: 28603504; PMCID: PMC5445139. 

  3. Stavric B, Klassen R, Watkinson B, Karpinski K, Stapley R, Fried P. Variability in caffeine consumption from coffee and tea: possible significance for epidemiological studies. Food Chem Toxicol. 1988 Feb;26(2):111-8. doi: 10.1016/0278-6915(88)90107-x. PMID: 3366410.

  4. DePaula J, Farah A. Caffeine Consumption through Coffee: Content in the Beverage, Metabolism, Health Benefits and Risks. Beverages. 2019; 5(2):37. https://doi.org/10.3390/beverages5020037

  5. Modi AA, Feld JJ, Park Y, Kleiner DE, Everhart JE, Liang TJ, Hoofnagle JH. Increased caffeine consumption is associated with reduced hepatic fibrosis. Hepatology. 2010 Jan;51(1):201-9. doi: 10.1002/hep.23279. PMID: 20034049; PMCID: PMC2801884.

  6. Ricardo Rohweder, et. al Caffeine intake during pregnancy and adverse outcomes: An integrative review, Reproductive Toxicology,

    Volume 123,2024,108518,ISSN 0890-6238, https://doi.org/10.1016/j.reprotox.2023.108518.

    https://www.nhs.uk/pregnancy/keeping-well/foods-to-avoid/

  7. Drugs and Lactation Database (LactMed®) [Internet]. Bethesda (MD): National Institute of Child Health and Human Development; 2006-. Caffeine. [Updated 2024 Jan 15]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK501467/

  8. Temple JL. Caffeine use in children: what we know, what we have left to learn, and why we should worry. Neurosci Biobehav Rev. 2009 Jun;33(6):793-806. doi: 10.1016/j.neubiorev.2009.01.001. Epub 2009 Jan 20. PMID: 19428492; PMCID: PMC2699625.

  9. Antonio J, Newmire DE, Stout JR, et al. Common questions and misconceptions about caffeine supplementation: what does the scientific evidence really show?. J Int Soc Sports Nutr. 2024;21(1):2323919. doi:10.1080/15502783.2024.2323919

  10. Rodak K, Kokot I, Kratz EM. Caffeine as a Factor Influencing the Functioning of the Human Body-Friend or Foe? Nutrients. 2021 Sep 2;13(9):3088. doi: 10.3390/nu13093088. PMID: 34578966; PMCID: PMC8467199.

  11. Sajadi-Ernazarova KR, Hamilton RJ. Caffeine Withdrawal. [Updated 2023 Aug 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK430790/

  12. Herden L, Weissert R. The Impact of Coffee and Caffeine on Multiple Sclerosis Compared to Other Neurodegenerative Diseases. Front Nutr. 2018 Dec 21;5:133. doi: 10.3389/fnut.2018.00133. PMID: 30622948; PMCID: PMC6308803.

Vibhaavari Venkatesh is a Registered Associate Nutritionist and Dietetic Assistant Practitioner with the NHS. Her journey into the field of nutrition began in India, where she earned a Bachelor’s degree in Clinical Nutrition, followed by a Master’s in Human Nutrition with a specialisation in Obesity and Weight Management from the University of Glasgow. With a passion for evidence-based nutrition, she aims to share valuable insights on a range of topics, starting with the science of caffeine - exploring its benefits, effects on daily life, and strategies for mindful consumption.

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