Caffeine is a plant compound and stimulant (methylxanthine). It has a similar structure to other plant compounds like theobromine, xanthine, and theophylline [R, R].

For the average person, coffee or tea is their main source of caffeine. Coffea arabicaand Coffea canephora (Robusta) are two types of plants that produce coffee beans. Meanwhile, the Camellia sinensis leaves are used for black, green, and white teas [R, R].

Although coffee and tea both contain caffeine, they can have different effects on our health. This may be due to their different amounts of caffeine or other components. While coffee also contains diterpene alcohols that can raise cholesterol, tea contains polyphenols, which have many health benefits [R, R].

Caffeine is consumed around the world for its beneficial effects on energy, physical and mental performance, alertness, and mood. Many people praise its ability to keep them awake and focused on their tasks. Additionally, most of its side effects tend to decrease with prolonged consumption.  [R].

Mechanisms of Action

Caffeine Inhibits Adenosine

Since caffeine’s structure is similar to adenosine, it can block adenosine receptors (mainly A1 and A2A). It increases the activation of the sympathetic (fight-or-flight) nervous system, which results in stimulatory effects [R].

Consumers may feel more energized and awake due to caffeine blocking A1 receptors. This also causes heart-pounding effects [R].

Caffeine Inhibits Phosphodiesterase

Caffeine binds to phosphodiesterase receptors and blocks phosphodiesterase activity. As less phosphodiesterase receptor molecules become available, cAMP cannot bind to the receptors and it accumulates in the cells. This produces effects such as vasodilation (widening of blood vessels), and fat oxidation (breakdown) [R, R].

Health Benefits

1) Caffeine Improves Attention and Alertness

In a study (DB-RCT) of 36 participants, caffeine exhibited dose-dependent effects on alertness and attention. When people who usually do not drink caffeinated products consumed high doses of caffeine, they had a higher increase in brain function. Regular and tolerant users may still feel the same effects, but to a smaller extent [R].

A lack of sleep can cause delays in reaction times. In a study (SB-RCT) of 20 sleep-deprived participants, a total daily dose of 800 mg of caffeine helped improve reaction speed and accuracy [R].

Caffeine helps keep you alert and awake while driving. In one study (SB-RCT), twelve young adults either had sufficient sleep (9 hours) or a lack-of-sleep (4 hours). 100 mg of caffeine improved both groups’ coordination, judgment, memory, and reaction time during a driving task [R].

2) Caffeine Increases Strength and Endurance

Caffeine appears to help anaerobic exercises like sprinting or jumping. This effect may arise from its anti-fatigue effects and by improving endurance, physical strength, and power output [R].

In a study (SB-RCT) of 16 recreationally trained young men, caffeine improved upper and lower body muscle force. It improved smaller muscle strength by 6% and larger muscles by more than 13% [R].

It also positively affects metabolic rate and increases oxygen uptake. When you can take in more oxygen, utilizing it at maximum exertion, you have better athletic performance [R].

In a study (DB-RCT) of 14 well-trained men, their power output significantly increased after caffeine ingestion, improving their sprint performance [R].

Delaying the onset of fatigue is caffeine’s most pronounced effect. In a study (DB-RCT) of 10 female karate athletes, a moderate dose reduced perceived exertion and pain [R].

When caffeine delays fatigue, the body’s muscles can contract more forcefully. People may exercise longer and eventually increase their training volume or overall work. Aerobic exercise such as running, jogging, cardio workout, swimming, and biking can benefit the most from increased training volume [R].

In a study of 24 professional rugby players, an 800-mg dose of caffeine increased their testosterone by 21% during exercise, compared to 15% without caffeine. However, it also increased cortisol levels [R].

3) Caffeine Prevents Weight Gain

Caffeine is a popular ingredient in over-the-counter fat burning supplements. It can increase energy usage and improve metabolic rate, which helps prevent weight gain [R].

In a study of ten lean and ten obese women, both groups produced more body heat, spent more energy, and had increased fat oxidation (breakdown) after coffeeingestion. Their increase in energy usage was short-lived compared to fat breakdown [R].

In a study of healthy and obese individuals, 4 different studies (including a DB-RCT) showed that caffeine increased free fatty acid (FFA) levels and fat breakdown [R].

By breaking down stored fat, caffeine shows benefits in weight loss management. In a study of 2,100 participants, the ones who drank 2 to 4 cups of caffeinated coffee a day were more successful at shedding weight than those who did not [R].

4) Caffeine Can Improve Mood

For some people, 200 to 250 mg of caffeine may improve their mood for up to 3 hours [R].

In a large cohort study of 43,599 men and 164,825 women, people who consumed caffeinated coffee had a lower rate of suicide. This could be due to caffeine’s ability to increase dopamine [R].

However, higher amounts (600 mg) can increase tension and anxiety, which can negatively affect mood [R].

5) Caffeine Protects Against Parkinson’s Disease

Caffeine is neuroprotective and can prevent nerve cell degeneration, which occurs in Parkinson’s [R].

Additionally, by inhibiting adenosine receptors, it improves mobility and motor functions in Parkinson’s patients [R].

In a study (DB-RCT) of 61 Parkinson’s patients, 100 mg of caffeine twice daily for 3 weeks reduced movement slowness (bradykinesia). However, it had no other effects on Parkinson’s symptoms [R].

In one study, out of 430 healthy subjects, those who consumed caffeinated coffee had a lower risk of developing Parkinson’s disease. It even reduced the risk in those genetically predisposed to develop the condition [R].

Additionally, in a study of 29,000 participants, both habitual coffee and tea drinkers had a lower risk for Parkinson’s [R].

6) Caffeine May Enhance Memory

In a study (DB-RCT) of 95 healthy young adults, moderate doses of caffeine (200 mg) increased memory performance. Although the results were not significant, high to moderate caffeine users had increased memory recall compared to low users [R].

In another study, 140 young adults participated in two experiments. The participants that consumed caffeinated coffee in the morning had significantly better performances on a memory recall test in the early morning, but not in the late afternoon [R].

However, a review concluded that caffeine was inconsistent in its effects on memory. It was the most beneficial on improving memory during simple tasks, but not complex ones [R].

7) Caffeine Reduces Dementia and Alzheimer’s Disease Risk

In a long-term study of 1,400 people, drinking 3 to 5 cups of coffee per day at midlife could decrease dementia or AD risk by about 65% during their elderly years [R].

In a review, coffee had a positive effect on brain function. Moderate caffeinated coffee consumption (around 4 cups) decreased the risk of dementia and Alzheimer’s later in life. However, caffeinated tea had no effect on dementia or Alzheimer’s risk [R].

In mice, caffeine suppressed amyloid beta production. Amyloid beta contributes to brain inflammation and the onset of Alzheimer’s disease. Thus, caffeine can protect and restore brain function [R].

8) Caffeine Protects the Liver

Caffeine is associated with a lower risk of liver fibrosis (scar tissue in the liver). In a study of 306 patients with fatty liver disease, people who drank caffeinated coffee had less severe liver scarring than the ones who did not drink caffeinated coffee [R].

In a cross-sectional study of 910 veterans with chronic hepatitis C, a minimum of 100 mg of caffeine daily reduced the odds of liver tissue scarring [R].

Additionally, in a survey of 177 liver biopsy patients, caffeine consumption was associated with less severe liver tissue scarring. Two cups of coffee daily helped reduce the severity of tissue scarring [R].

A study of 274 cirrhosis cases and 458 healthy individuals found that caffeinated coffee prevented liver cirrhosis (chronic liver damage). However, intake from sources other than coffee (such as tea or energy drinks) did not show the same benefits [R].

9) Caffeine Prevents/Combats Cancer

Caffeine May Reduce Mouth and Throat Cancer Risk

A 26-year cohort study examined almost 1 million men and women to look at the association between caffeine and oral/pharyngeal (mouth and throat) cancer [R].

There was an association between high caffeinated coffee intake and reduced risk of oral cancer. Those who consumed 4 to 6 cups of caffeinated coffee daily reduced their cancer risk by approximately 50% [R].

Caffeine May Reduce Colon Cancer Risk

Colorectal cancer may be either proximal, distal, or rectal cancer. Proximal cancer affects the first and middle parts of the colon. Proximal tumors are associated with a higher death rate in colon cancer [R].

In a cohort study of 489,706 participants, there was an inverse association between caffeinated coffee and colon cancer risk. People who drank 4to 5 cups of coffee daily had a lower risk of colon cancer and proximal tumors [R].

However, there was no link between caffeine and reduced rectal cancer risk in a different, 2 million person cohort study [R].

Caffeine Prevents Skin Cancer

In a cohort study of more than 4 million subjects, caffeinated coffee drinkers had a lower risk of developing melanoma (skin cancer) than those who did not drink caffeine [R].

In rats with skin cancer, caffeinated tea consumption decreased the number of tumors and fat levels. Reducing fat levels in the skin can decrease tumor formation [R].

Caffeine Reduces Liver Cancer Risk

Liver cancer is normally a secondary cancer that happens when cancer cells spread from other parts of the body. However, hepatitis, tissue scarring, and chronic liver damage may cause primary liver cancer [R].

A review of 4 cohort and 5 case-control studies found a 43% decreased risk of liver cancer with the consumption of 2 cups of caffeinated coffee daily [R].

10) Caffeine Protects the Skin

Caffeine has antioxidant properties that can help protect skin cells against UV radiation and skin aging due to sun exposure. Additionally, it is used in cosmetic products to prevent fat accumulation and cellulite formation [R].

In a study (DB-RCT) of 40 dermatitis patients, a topical cream containing 30% caffeine helped reduce redness, itchiness, scaling, and oozing [R].

11) Caffeine Relieves Asthma

A review of 7 studies showed that caffeine could open airways and relieve bronchitis symptoms including wheezing, coughing, and breathlessness [R].

When airways open, this helps people with asthma breathe easier. The effect is similar to theophylline, a common asthma drug. Theophylline and caffeine are very similar in structure. However, caffeine’s effects are short-lived and last only up to 4 hours [R].

12) Caffeine May Lower the Risk of Type 2 Diabetes

Consumption of caffeine may lower your risk of getting type 2 diabetes. In a prospective cohort study of nearly 90,000 healthy women, moderate caffeinated coffee consumption lowered the risk of type 2 diabetes in younger and middle-aged women [R].

Another review of 8 prospective studies also showed that drinking caffeinated coffee is associated with a reduced risk of type 2 diabetes [R].

13) Caffeine May Prevent Erectile Dysfunction

A cohort study of 3,700 men showed that those who drank 2 to 3 cups of caffeinated coffee daily had lower risk of erectile dysfunction. While healthy, overweight, and men with high blood pressure experienced these results, caffeine did not help diabetic men [R].

14) Caffeine Reduces Kidney Stone Risk

In a 20-year cohort study of 217,883 healthy participants, high caffeine intake was associated with a reduced risk of kidney stones [R].

Caffeine increases urinary excretion of calcium, which may cause kidney stone formation. However, at the same time, the higher intake of caffeine diluted urine and reduced kidney stone risk [R].

15) Caffeine May Prevent Tinnitus

In a prospective study of 6,500 women, the women who consumed the most caffeine had the lowest reported incidence of tinnitus (ringing in the ears) [R].

16) Caffeine Might Help Relieve Pain

There is a link between sleep deprivation and hyperalgesia (heightened sensitivity to pain) [R].

In mice, common painkillers (ibuprofen and morphine) had no noticeable effects on sleep-deprived mice. In contrast, caffeine relieved pain in sleep-deprived mice but not in normal mice [R].

17) Caffeine May Prevent Gout

In a prospective study of 89,000 women, caffeinated coffee (but not tea) was associated with a lower risk of gout [R].

Side Effects

Some of the most common side effects are [R]:

• Restlessness
• Nervousness
• Excitement
• Dizziness
• Flushed face
• Increased urination
• Diarrhea
• Vomiting
• Muscle twitching
• Rambling flow of thought and speech

However, most of caffeine’s side effects tend to decrease with prolonged consumption and tolerance.