How Does Caffeine Affect Physical Health and Performance?

Caffeine is a widely consumed substance that can affect your body and mind. It is found naturally in coffee, tea, cocoa, guarana, and chocolate, as well as in some medicines and energy drinks.

Caffeine can stimulate your brain and nervous system, increase your alertness and energy, enhance your mood and endurance, and help you burn fat.

But how does caffeine affect your physical health and performance?

In this article, we will explore the benefits and risks of caffeine for your health and fitness.

Caffeine and the Nervous System

Caffeine works by blocking the effects of adenosine, a chemical that makes you feel sleepy and relaxed. By doing so, caffeine increases the activity of your brain and nervous system, making you more alert, focused, and motivated.

Caffeine can also boost dopamine, serotonin, and norepinephrine levels, which are involved in mood, learning, memory, and reward. Caffeine can improve cognitive functions, such as attention, reaction time, memory, and problem-solving (Smith, 2002; Nehlig, 2010)^{18 13}.

However, caffeine can also cause anxiety, jitteriness, insomnia, and headaches if you consume too much or are sensitive to it (James & Rogers, 2005)⁹.

Caffeine and the Hormones

Caffeine can affect your hormones in various ways. One of the most notable effects is the increase of epinephrine (also known as adrenaline), the hormone that prepares your body for action.

Epinephrine increases your heart rate, blood pressure, breathing, and blood flow to your muscles, improving your physical performance and endurance (Graham & Spriet, 1995)⁵.

Caffeine can also increase cortisol levels, the hormone regulating stress response. Cortisol can help you cope with short-term stress, but chronic high cortisol levels can negatively affect your immune system, metabolism, and mood (Lovallo et al., 2006)¹¹.

Caffeine can also influence your insulin sensitivity, which affects how your body uses glucose for energy. Caffeine can reduce your insulin sensitivity, which can impair your glucose metabolism and increase your risk of type 2 diabetes (Thong et al., 2002)²⁰.

Caffeine and the Muscles

Caffeine can stimulate your motor neurons, which control your muscle contractions. This can increase muscle strength, power, and endurance, especially for high-intensity and short-duration exercises (Tarnopolsky, 2008; Grgic et al., 2019)^{19 6}.

Caffeine can also enhance muscle recovery by reducing the perception of pain and fatigue and increasing the uptake of glucose and glycogen, the main sources of energy for your muscles (Pedersen et al., 2008; Hurley et al., 2013)^{14 8}.

However, caffeine can also interfere with muscle relaxation, impairing muscle coordination and flexibility (Santos et al., 2012)¹⁶.

Caffeine and Fat Burning

Caffeine can help you burn fat by increasing your metabolic rate, and the calories you burn at rest. Caffeine can also stimulate the breakdown of fat in your fat cells and increase the use of fat as fuel for your muscles (Astrup et al., 1990; Gonzalez et al., 2020)^{2 4}.

Caffeine can also suppress your appetite, which can help you reduce your calorie intake (Schubert et al., 2017)¹⁷. However, caffeine can also reduce your fat burning if you consume it with sugar or milk, which can counteract its effects by increasing your insulin levels (Keijzers et al., 2002)¹⁰.

Moreover, caffeine can lose effectiveness over time as your body becomes tolerant (Robertson et al., 1981)¹⁵.

Consume Caffeine in Moderation

Caffeine can improve your alertness, mood, endurance, strength, recovery, and fat-burning, but it can also cause anxiety, insomnia, headaches, hormonal imbalance, glucose impairment, and muscle tension.

The key to enjoying the benefits of caffeine and avoiding the risks is to consume it in moderation and according to your individual needs and preferences. Caffeine can be a useful tool to enhance your health and fitness, but it should not substitute for a balanced diet, regular exercise, and adequate sleep.

The safe amount of caffeine depends on several factors, such as your body weight, age, health condition, tolerance, and sensitivity.

The general recommendation for healthy adults is to limit their caffeine intake to no more than 400 mg per day (EFSA, 2015)³.
For children and adolescents, the recommended limit is no more than 3 mg per kg of body weight per day (Health Canada, 2012)⁷.
For pregnant and breastfeeding women, the recommended limit is no more than 200 mg per day (ACOG, 2010)¹.
People with certain medical conditions, such as high blood pressure, heart problems, anxiety, insomnia, or ulcers, should consult their doctor before consuming caffeine or reduce their intake accordingly (Mayo Clinic, 2020)¹².

Sources and References

ACOG. (2010). Moderate caffeine consumption during pregnancy. https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2010/08/moderate-caffeine-consumption-during-pregnancy
Astrup, A., Toubro, S., Cannon, S., Hein, P., Breum, L., & Madsen, J. (1990). Caffeine: a double-blind, placebo-controlled study of its thermogenic, metabolic, and cardiovascular effects in healthy volunteers. The American Journal of Clinical Nutrition, 51(5), 759–767. https://doi.org/10.1093/ajcn/51.5.759
EFSA. (2015). Scientific opinion on the safety of caffeine. EFSA Journal, 13(5), 4102. https://doi.org/10.2903/j.efsa.2015.4102
Gonzalez, J. T., Stevenson, E. J., Rumbold, P. L. S., & Betts, J. A. (2020). Caffeine increases maximal fat oxidation during a graded exercise test: is there a diurnal variation? Journal of the International Society of Sports Nutrition, 17(1), 61. https://doi.org/10.1186/s12970-020-00383-4
Graham, T. E., & Spriet, L. L. (1995). Metabolic, catecholamine, and exercise performance responses to various doses of caffeine. Journal of Applied Physiology, 78(3), 867–874. https://doi.org/10.1152/jappl.1995.78.3.867
Grgic, J., Trexler, E. T., Lazinica, B., & Pedisic, Z. (2019). Effects of caffeine intake on muscle strength and power: a systematic review and meta-analysis. Journal of the International Society of Sports Nutrition, 16(1), 11. https://doi.org/10.1186/s12970-019-0287-1
Health Canada. (2012). Caffeine in food. https://www.canada.ca/en/health-canada/services/food-nutrition/food-safety/food-additives/caffeine-foods/foods.html
Hurley, C. F., Hatfield, D. L., & Riebe, D. A. (2013). The effect of caffeine ingestion on delayed onset muscle soreness. The Journal of Strength & Conditioning Research, 27(11), 3101–3109. https://doi.org/10.1519/JSC.0b013e3182a99477
James, J. E., & Rogers, P. J. (2005). Effects of caffeine on performance and mood: withdrawal reversal is the most plausible explanation. Psychopharmacology, 182(1), 1–8. https://doi.org/10.1007/s00213-005-0084-6
Keijzers, G. B., De Galan, B. E., Tack, C. J., & Smits, P. (2002). Caffeine can decrease insulin sensitivity in humans. Diabetes Care, 25(2), 364–369. https://doi.org/10.2337/diacare.25.2.364
Lovallo, W. R., Whitsett, T. L., al’Absi, M., Sung, B. H., Vincent, A. S., & Wilson, M. F. (2006). Caffeine stimulation of cortisol secretion across the waking hours in relation to caffeine intake levels. Psychosomatic Medicine, 68(5), 769–776. https://doi.org/10.1097/01.psy.0000234758.90677.0f
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Nehlig, A. (2010). Is caffeine a cognitive enhancer? Journal of Alzheimer’s Disease, 20(Supplement 1), S1–S5. https://doi.org/10.3233/JAD-2010-091315
Pedersen, D. J., Lessard, S. J., Coffey, V. G., Churchley, E. G., Wootton, A. M., Ng, T., Watt, M. J., & Hawley, J. A. (2008). High rates of muscle glycogen resynthesis after exhaustive exercise when carbohydrate is coingested with caffeine. Journal of Applied Physiology, 105(1), 7–13. https://doi.org/10.1152/japplphysiol.01121.2007
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Santos, R. V., Landeira-Fernandez, J., Paes, F., de Oliveira, L., de Souza, H. S., da Silva, A. C., & Laks, J. (2012). Caffeine affects the muscular performance and plasma redox status of young trained and untrained men. Journal of Caffeine Research, 2(3), 111–117. https://doi.org/10.1089/jcr.2012.0011
Schubert, M. M., Irwin, C., Seay, R. F., Clarke, H. E., Allegro, D., & Desbrow, B. (2017). Caffeine, coffee, and appetite control: a review. International Journal of Food Sciences and Nutrition, 68(8), 901–912. https://doi.org/10.1080/09637486.2017.1320537
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Thong, F. S., Graham, T. E., & Heigenhauser, G. J. (2002). The role of free fatty acids in regulating exercise- and insulin-stimulated glucose uptake in rat skeletal muscle. American Journal of Physiology. Endocrinology and Metabolism, 283(1), E146–E153. https://doi.org/10.1152/ajpendo.00499.2001