Caffeine
Brief description
Caffeine is naturally found in coffee, tea and chocolate. It works as a stimulant on the central nervous system, resulting in an increase in heart rate, blood pressure and urine output.
Evidence base
Increase in muscle strength, endurance & power – findings collated from multiple systematic reviews(1, 2).
Improvement in reaction time, attention and memory when taken before and or during exercise(3). Additionally, on sleep deprived individuals, caffeine can improve performance on attention, information processing tasks, and driving ability(4).
Weight loss – A systematic review of 13 studies (606 participants) found that for every doubling in caffeine intake, the mean reduction in weight, BMI and fat mass increased 2 fold. Many interventions did have other supplements as part of the intervention, including ephedrine (a powerful weight loss stimulant)(5). In other studies, caffeine has been shown to increase fat metabolism at rest(6) and during exercise(7) – however only in the region of 100kcal/day.
Recommended serving & duration.
Some studies have suggested taking caffeine supplements at least 9 hours before bed to avoid poor sleep duration and or quality(8).
For sports performance – 3-6mg/kg of bodyweight (approx. 200-400mg for a 70kg person). Start with the lower suggestion to achieve a smaller risk of side effects(9).
Safety & tolerability
The Food and Drug Administration (FDA) and European Food Safety Authority (EFSA) report that a total dosage of up to 400mg/day is generally considered safe in non-pregnant adults(10, 11).
Generally short-lived side effects are noted and include:
Heart palpitations, light-headedness, headache, increased urination, nausea, diarrhoea, anxiety, and raised blood pressure.
Caffeine will impair sleep if consumed too late(8).
Regular use of caffeine may reduce the frequency or incidence of these side effects.
Caffeine may also cause mild dependance, and so withdrawal from caffeine can cause: irritability, drowsiness, agitation, headache(12).
If there is any doubt about whether it is safe to consume caffeine, please consult your healthcare provider. Avoid with pre-existing heart arrhythmias.
References:
Grgic J, Trexler ET, Lazinica B, Pedisic Z. Effects of caffeine intake on muscle strength and power: a systematic review and meta-analysis. J Int Soc Sports Nutr. 2018;15:11.
Grgic J, Grgic I, Pickering C, Schoenfeld BJ, Bishop DJ, Pedisic Z. Wake up and smell the coffee: caffeine supplementation and exercise performance-an umbrella review of 21 published meta-analyses. Br J Sports Med. 2020;54(11):681-8.
Lorenzo Calvo J, Fei X, Domínguez R, Pareja-Galeano H. Caffeine and Cognitive Functions in Sports: A Systematic Review and Meta-Analysis. Nutrients. 2021;13(3).
Irwin C, Khalesi S, Desbrow B, McCartney D. Effects of acute caffeine consumption following sleep loss on cognitive, physical, occupational and driving performance: A systematic review and meta-analysis. Neurosci Biobehav Rev. 2020;108:877-88.
Tabrizi R, Saneei P, Lankarani KB, Akbari M, Kolahdooz F, Esmaillzadeh A, et al. The effects of caffeine intake on weight loss: a systematic review and dos-response meta-analysis of randomized controlled trials. Crit Rev Food Sci Nutr. 2019;59(16):2688-96.
Conger SA, Tuthill LM, Millard-Stafford ML. Does Caffeine Increase Fat Metabolism? A Systematic Review and Meta-Analysis. Int J Sport Nutr Exerc Metab. 2023;33(2):112-20.
Collado-Mateo D, Lavín-Pérez AM, Merellano-Navarro E, Coso JD. Effect of Acute Caffeine Intake on the Fat Oxidation Rate during Exercise: A Systematic Review and Meta-Analysis. Nutrients. 2020;12(12).
Gardiner C, Weakley J, Burke LM, Roach GD, Sargent C, Maniar N, et al. The effect of caffeine on subsequent sleep: A systematic review and meta-analysis. Sleep Med Rev. 2023;69:101764.
Kerksick CM, Wilborn CD, Roberts MD, Smith-Ryan A, Kleiner SM, Jäger R, et al. ISSN exercise & sports nutrition review update: research & recommendations. Journal of the International Society of Sports Nutrition. 2018;15(1):38.
EFSA Panel on Dietetic Products N, Allergies. Scientific Opinion on the safety of caffeine. EFSA Journal. 2015;13(5):4102.
FDA. Spilling the Beans: How Much Caffeine is Too Much? 2023 [Available from: https://www.fda.gov/consumers/consumer-updates/spilling-beans-how-much-caffeine-too-much.
Juliano LM, Griffiths RR. A critical review of caffeine withdrawal: empirical validation of symptoms and signs, incidence, severity, and associated features. Psychopharmacology (Berl). 2004;176(1):1-29.
