What Is Caffeine? Health Benefits, Sources, And Side Effects

Written by Sindhu Koganti

Caffeine is the most common morning energizer that most of us prefer to kickstart our day. A steaming cup of coffee or tea stimulates our senses and has several health benefits. It is the most common psychoactive drug that stimulates the central nervous system and prevents drowsiness. Caffeine is found in many beverages, chocolates, and even decaffeinated products. It contains antioxidants, flavonoids, and polyphenols and does more than just turbocharge you for the day. Want to know how? Keep reading to understand the health benefits of caffeine, dosage, possible side effects, and some myths associated with it.

How Caffeine Works

Caffeine has an immediate effect and gets absorbed into the blood in just 15 minutes. It is a psychoactive drug, meaning it can influence the brain and nervous system’s function. Caffeine activates different neuronal pathways by altering the release of neurotransmitters (signaling molecules released by the neurons). Consuming caffeine blocks adenosine (an inhibitory neurotransmitter that makes you feel tired and promotes sleep) to reduce fatigue and keep you alert (1), (2).

Coffee, tea, carbonated, and energy drinks contain high amounts of caffeine. Scroll down to find out the amount of caffeine content in different beverages.

What Drinks Contain Caffeine?

Here is the list of the most common sources of caffeine (3):

Sources Of Caffeine

Caffeine Content (per 8 ounces)

Decaffeinated coffee

3-12 mg

Instant coffee

27-173 mg

Plain brewed coffee

102-200 mg


240-720 mg

Brewed tea

40-120 mg

Green tea

30-50 mg

Black tea

25-110 mg

Soft drinks

20-40 mg

Energy drinks

50-160 mg

In addition, dark chocolate contains 5,035 mg of caffeine. Consuming caffeine has several benefits. Check them out.

Health Benefits Of Caffeine

1. Improves Brain Function

Caffeine is a central nervous system stimulant and can increase energy metabolism in the brain (4). It reduces cognitive decline, increases alertness, improves brain function, minimizes the risk of depression, and helps to focus and concentrate (5), (6), (7). Caffeine enhances long-term memory, and its regular consumption in limited amounts can reduce the risk of stroke, dementia, Alzheimer’s disease, and Parkinson’s disease (8), (9), (10), (11), (12).

2. May Help With Weight Loss

Caffeine intake may support weight loss, reduce BMI and body fat, and help manage optimal body weight (13), (14). A study conducted by Maastricht University, Netherlands, found that high caffeine intake promoted weight loss through fat oxidation and thermogenesis (15). In addition, it can prevent weight regain and be used as an alternative treatment for weight loss (16). Another study conducted on 18,417 men and 39,740 women found that increased caffeine intake may reduce long-term weight gain (17).

3. Enhances Exercise Performance

Caffeine supplements (about 2-9 mg per day) can enhance exercise performance (18),(19). In addition, it is used as an ergogenic aid that enhances endurance and performance during prolonged exercise. A study conducted by the University of Birmingham, United Kingdom, found that consuming 5mg/kg caffeine one hour before exercise could improve exercise performance(20), (21).

4. Improves Heart Health

Consuming caffeinated beverages like coffee is associated with a decreased risk of cardiovascular diseases (22), (23). A study conducted by the University of Singapore and National University Health System, Singapore, has found that coffee can lower the risk of stroke and heart failure (24). Moderate coffee consumption lowers the risk of coronary heart disease in women (25).

5. Prevents Diabetes

A study evaluated the link between coffee and the risk of type 2 diabetes. Researchers found that drinking more than a cup of coffee lowered the risk of type 2 diabetes (26 ). With every 200 mg per day of caffeine intake, the risk of diabetes drops by 12-14%. A review published in the Journal of Traditional and Complementary Medicine suggests that coffee consumption lowers the risk of type 2 diabetes (27),(28).

6. Protects Against Cancer

Caffeine has anticarcinogenic properties and can help protect against certain cancers, including colon, oral, prostate, breast, and skin cancers. It increases large bowel mobility and can effectively inhibit the risk of colorectal cancer (29), (30).

Caffeine contains antioxidants, anti-mutagen, and diterpenes, which may also reduce the risk of oral cancer. It has antiproliferative and antimetastatic properties that help inhibit the growth of prostate cancer cell lines. In addition, the chemoprotective activity of caffeine reduces the risk of nonmelanoma skin cancer (31), (32), (33).

An animal study found that eye drop preparation containing 72 mM caffeine inhibited cataract formation and showed a potential benefit in preventing diabetic cataracts (34). In addition, trigonelline, a bioactive in caffeine, has protective effects against kidney stone formation (35).

Intake of caffeine in limited quantities is safe. But how much should you drink? Find out this in the following section.

How Much Caffeine Is Too Much?

About five cups of coffee (400 mg daily) is considered safe for healthy adults (9). However, pregnant women should limit their caffeine intake to 200 mg per day (36). Excess caffeine intake has several side effects.

What Are The Side Effects Of Caffeine?

Excess caffeine intake may cause (37), (38):

  • Anxiety
  • Sleeplessness
  • Unstable bladder
  • Gastric irritation
  • Risk of miscarriage and fetal growth restriction
  • Cardiac abnormality

Melissa Mitri, MS, RDN, says, “Some people are more sensitive to caffeine than others, and so it is important to know the signs that your body is not responding well to it.” Excessive caffeine can spike blood pressure, increase arterial stiffness, and increase the risk of chronic headaches (39), (40).

Caffeine consumption before pregnancy increases the risk of miscarriage and may lead to a progressive decrease in fertility levels (41), (42). In addition, caffeine consumption (10 or more cups per day) during lactation can affect the infant, hamper sleep, and make them jittery and fussy (37). It can also interact with over-the-counter and prescription medications (43).

Caffeine has its benefits and recognized risks. But most often, it is misunderstood as a dangerous stimulant. In the next section, we have busted several myths associated with caffeine.

Myths Associated With Caffeine

Myth 1. Caffeine Is Addictive

No. It is not as caffeine cannot stimulate the pathways in your brain that are related to addiction. Some people may experience drowsiness, headaches, lethargy, or fatigue if they suddenly stop consuming caffeine (44). However, these usually last for a day or two. So, if you are trying to ditch caffeine, do it gradually to avoid these symptoms.

Myth 2. Caffeine Increases The Risk Of Heart Disease

It may increase blood pressure in people sensitive to caffeine, but not in healthy adults. Hence, if you have any heart problems or hypertension, please consult your doctor about your caffeine dosage.

Myth 3. Caffeine Is A Diuretic

There is no research to prove this claim. However, caffeine consumption has been associated with increased urine frequency and volume, which causes water and electrolytes loss. However, caffeine is not directly linked to fluid loss.

To Conclude

Most of us prefer caffeine to help us get going in the morning. It is an excellent stimulant, improves brain function, and has anti-cancer properties. However, ensure you consume it in moderate amounts, as excessive caffeine intake can affect your heart health and cause anxiety, sleeplessness, and other adverse effects. Hence, consult a doctor and limit your caffeine intake to avoid potential overdose and adverse health effects.


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  1. Caffeine: Cognitive and Physical Performance Enhancer or Psychoactive Drug?
  2. The role and regulation of adenosine in the central nervous system
  3. Caffeine (1 3 7-trimethylxanthine) in Foods: A Comprehensive Review on Consumption Functionality Safety and Regulatory Matters
  4. Caffeine and the central nervous system: mechanisms of action biochemical metabolic and psychostimulant effects
  5. Beneficial Role of Coffee and Caffeine in Neurodegenerative Diseases: A Minireview
  6. Is caffeine a cognitive enhancer?
  7. Adenosine Adenosine Receptors and the Actions of Caffeine
  8. Post-study caffeine administration enhances memory consolidation in humans
  9. Effects of coffee/caffeine on brain health and disease: What should I tell my patients?
  10. From epidemiology to pathophysiology: what about caffeine in Alzheimer\’s disease?
  11. Caffeine intake and dementia: systematic review and meta-analysis
  12. Dose-response meta-analysis on coffee tea and caffeine consumption with risk of Parkinson\’s disease
  13. The effects of caffeine intake on weight loss: a systematic review and dos-response meta-analysis of randomized controlled trials
  14. Caffeine intake is related to successful weight loss maintenance
  15. Body weight loss and weight maintenance in relation to habitual caffeine intake and green tea supplementation
  16. Caffeine Treatment Prevented from Weight Regain after Calorie Shifting Diet Induced Weight Loss
  17. Changes in caffeine intake and long-term weight change in men and women
  18. Caffeine and Exercise Performance: Possible Directions for Definitive Findings
  19. Caffeine and Exercise: What Next?
  20. Caffeine and exercise
  21. The metabolic and performance effects of caffeine compared to coffee during endurance exercise
  22. Association of Coffee Consumption With Total and Cause-Specific Mortality Among Nonwhite Populations
  23. Effects of habitual coffee consumption on cardiometabolic disease cardiovascular health and all-cause mortality
  24. Coffee consumption and cardiovascular health: getting to the heart of the matter
  25. Coffee consumption and risk of coronary heart diseases: A meta-analysis of 21 prospective cohort studies
  26. Changes in coffee intake and subsequent risk of type 2 diabetes: three large cohorts of US men and women
  27. Coffee and caffeine intake and incidence of type 2 diabetes mellitus: a meta-analysis of prospective studies
  28. Effects of coffee consumption on glucose metabolism: A systematic review of clinical trials
  29. Coffee consumption and risk of cancers: a meta-analysis of cohort studies
  30. Espresso coffee caffeine and colon cancer
  31. Coffee is protective against oral and pharyngeal cancer: A systematic review and meta-analysis
  32. Reduction by coffee consumption of prostate cancer risk: Evidence from the Moli-sani cohort and cellular models
  33. Coffee tea caffeine and risk of nonmelanoma skin cancer in a Chinese population: The Singapore Chinese Health Study
  34. Effectiveness of topical caffeine in cataract prevention: Studies with galactose cataract
  35. Caffeine in Kidney Stone Disease: Risk or Benefit?
  36. ACOG CommitteeOpinion No. 462: Moderate caffeine consumption during pregnancy
  37. The Safety of Ingested Caffeine: A Comprehensive Review
  38. The Relationship of Caffeine Intake with Depression Anxiety Stress and Sleep in Korean Adolescents
  39. Acute and long-term cardiovascular effects of coffee: implications for coronary heart disease
  40. Caffeine as a risk factor for chronic daily headache: a population-based study
  41. Couples\’ pre-pregnancy caffeine consumption linked to miscarriage risk
  42. Inhibitory effect of caffeine on pacemaker activity in the oviduct is mediated by cAMP-regulated conductances
  43. The Effect of Coffee on Pharmacokinetic Properties of Drugs : A Review
  44. Is caffeine addictive?–a review of the literature

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Sindhu Koganti is a Biotechnology graduate and has been in the writing field for over 4 years now. She specializes in writing on Health and Wellness. She has hands-on experience in writing articles and press releases on Life Sciences and Healthcare, Food and Beverages, and Chemicals and Materials. When she’s not writing, she loves watching movies and listening to music. She also enjoys traveling.