Scientific evidence for and against caffeine

Uses based on scientific evidence

These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare professional.

Grade*
Apnea

In preterm infants, apnea is defined as the stoppage of breathing for 20 seconds or longer. It is one of the most common breathing disorders in the neonatal intensive care unit. Caffeine is a breathing stimulant commonly used to treat apnea. Scientific evidence supports the use of caffeine in the treatment and prevention of apnea in premature infants.

A
Cognitive performance

Caffeine has a long history of use for enhancing mood and cognitive (mental) function. Caffeine may be useful when consumed prior to a cognition-related task. It also appears to heighten working memory and improve reaction time, but it has less effect on long-term memory.

A
Exercise performance

Caffeine is a known stimulant that may enhance endurance and performance when used before exercise, particularly in low-to-moderate doses. Caffeine in dry form appears to be more beneficial than coffee or tea. However, its use as a performance-enhancing agent remains controversial. Caffeine should be used with caution, as it may increase blood pressure, heart rate, and urine flow.

A
Respiratory disorders

Caffeine is a weak type of methylxanthine. Methylxanthines are a class of drugs that open the airways and promote airflow. As such, these types of agents are used to help manage conditions whereby airflow is restricted, such as asthma and chronic obstructive pulmonary disease (COPD). Research suggests that caffeine reduces asthma symptoms, including exercise-induced airway constriction. Caffeine has also been suggested to reduce airway muscle fatigue.

A
Headaches

Evidence suggests that caffeine may have pain-relieving effects. In particular, caffeine has shown useful effects for relieving hypnic migraines (headaches that occur during sleep) and headaches that occur after punctures to the lower back. Although promising, more well-designed trials are needed in this area.

B
Attention-deficit hyperactivity disorder (ADHD)

There is conflicting evidence supporting the use of caffeine in the treatment of ADHD in children. Additional research is needed in this area.

C
Diabetes

Caffeine and coffee may lower the risk of type 2 diabetes and prevent exercise-induced low blood sugar in type 1 diabetes. However, the research in this area is not consistent, as caffeine has been previously associated with impaired glucose tolerance and insulin sensitivity. Additional research is needed in this area.

C
Intermittent claudication

Limited evidence suggests that caffeine may have positive effects on physical capacity in patients with intermittent claudication (muscle pain in the limbs). Additional research is needed to confirm early results.

C
Kwashiorkor (children)

Preliminary evidence suggests that caffeine improves alertness and appetite during the nutritional rehabilitation of children and may therefore have positive effects as an added therapy in the treatment of kwashiorkor (a form of childhood malnutrition). More high-quality research is needed in this area before any firm conclusions can be made.

C
Liver disease

Preliminary research suggests that caffeine may have beneficial effects against excess tissue buildup in the liver and that it may be associated with a lower risk of liver disease. However, well-designed trials are needed in this area before any firm conclusions can be drawn.

C
Mood

Caffeine is well known for its mood-changing effects. However, current evidence on the relationship between caffeine and depression risk is conflicting, with some studies showing beneficial effects and others showing a lack of effect. Further high-quality research is needed in this area before any firm conclusions can be made.

C
Obsessive compulsive disorder (OCD)

Limited evidence suggests that the effects of caffeine are similar to those of d-amphetamine. D-amphetamine is a drug known to promote alertness and focus. Although this is promising, additional research is needed to clarify these early findings.

C
Pain

Evidence suggests that caffeine may have pain-relieving effects. According to early research, caffeine has shown beneficial effects against headache- and muscle ache-related pain. More well-designed trials are needed in this area before any firm conclusions can be drawn.

C
Parkinson’s disease

Limited evidence suggests that increased coffee and caffeine consumption may be related to decreased risk of Parkinson’s disease. Further high-quality research is needed in this area before any firm conclusions can be drawn.

C
Skin conditions (wrinkles, stretch marks, cellulite)

The skin application of caffeine for the treatment of wrinkles, stretch marks, and cellulite is growing in popularity. However, the effect of caffeine alone cannot be determined, as most products contain a mixture of agents. Further research assessing the use of caffeine alone is needed in this area.

C
Stroke

Both theophylline and caffeine are types of methylxanthines. Methylxanthines are a class of drugs that narrow blood vessels in the brain. Due to this effect, early research suggests that theophylline may be useful in stroke patients. However, the effect of caffeine in this area is unclear. More high-quality trials are needed before a conclusion can be drawn.

C
Weight loss

Early research suggests that caffeine may be useful for weight loss, particularly when combined with other agents, such as green tea. Although caffeine has shown some positive effects on urine flow, exercise performance, heat production, and feelings of fullness, conflicting results have been seen with respect to its effects on blood sugar levels. Further studies are needed in this area before any firm conclusions can be drawn.

C

 

*Key to grades:

A: Strong scientific evidence for this use;
B: Good scientific evidence for this use;
C: Unclear scientific evidence for this use;
D: Fair scientific evidence against this use (it may not work);
F: Strong scientific evidence against this use (it likely does not work).

http://ww5.komen.org/BreastCancer/Caffeine.html

More research is needed

While some research has linked caffeine sources to some big benefits, our experts say the jury is still out.

“There’s some evidence that coffee or tea may be beneficial for weight management and lowering your disease risk, but whether that’s because of caffeine is not clear,” says Wenli Liu, M.D., associate professor in Internal Medicine at MD Anderson.

It’s possible, says Liu, that the antioxidants and other compounds in coffee and tea could explain the drinks’ health benefits.

The takeaway: Most studies linking coffee or tea to major health benefits aren’t conclusive and caffeine’s role is uncertain.

Caffeine can cause problems

“We know for certain that caffeine in high amounts can cause heart palpitations and arrhythmias,” Liu says. It also can worsen stomach ulcers.

Plus, if you drink caffeine in the form of soda or energy drinks, you could take in too many sugar calories, which could lead to weight gain. And being overweight or obese increases your risk for cancer and other diseases.


Scientists discovered that two genes determine whether you metabolize caffeine slowly or quickly. Together, these two genes are responsible for inherited differences in the way people process caffeine. They’re one reason why some people get amped from a single cup of coffee, while others down three cups before noon and another two at dinner, and never once jitter.

It’s in your genes, as the saying goes. Environmental factors, like whether you’re a smoker, still play a role. But genetic markers appear to explain a lot.

The two genes are known as CYP1A2, which has long been associated with caffeine (it produces an enzyme by the same name), and AHR, a gene that regulates the activity of CYP1A2. Researchers sifted through 300,000 genetic markers, before noticing that these two genes were essentially holding hands.

Slow and Fast Metabolizers

Every person has both of these genes, but CYP1A2 comes in two versions (or alleles; in this case differentiated by a single nucleotide). It’s like having a switch that is either turned on or off. This tiny variation makes you either a slow or fast metabolizer of caffeine ¬– it regulates how efficiently your liver breaks down and flushes caffeine from your system.

Slow metabolizers tend to drink less coffee (or other form of caffeine); fast metabolizers fuel up on more caffeine to keep feeling its effects. In one report, fast metabolizers averaged 40 mg more caffeine per day than did slow metabolizers.

In case you’re wondering, these particular caffeine genes don’t just regulate caffeine. They’re actually multi-taskers, and control other compounds, including ones related to certain cancers. (While we’re on the subject, different genes play a role in alcohol and nicotine addiction, too.)

In case you’re wondering, these particular caffeine genes don’t just regulate caffeine. They’re actually multi-taskers, and control other compounds, including ones related to certain cancers. (While we’re on the subject, different genes play a role in alcohol and nicotine addiction, too.)

The Caffeine Gene’s Split Personality

If you’re up for more complicated data: CYP1A2 also refers to an enzyme, generated by the gene CYP1A2 (genes are usually differentiated from their enzymes by italics). CYP is an abbreviation for a superfamily of enzymes and their encoding genes, known as cytochrome P450. The numbers and letters that follow CYP indicate the gene family, subfamily, and specific gene. Are your eyes glazing over yet? This may be too much information, but if you see CYP1A2 referenced as a both a gene and an enzyme, you’ll understand why.

Heart Attack Risk: What the Caffeine Gene Shows

One study based on 4,000 coffee drinkers used the CYP1A2 gene to identify slow and fast caffeine metabolizers, and their relationship to heart health. Slow metabolizers showed an increased risk of nonfatal heart attack. Women appeared to be at a slightly higher risk than men, probably because hormonal differences also slow caffeine’s breakdown in women.

For men and women, slow metabolizers showed increasing risk of nonfatal heart attack with increasing coffee consumption. Fast metabolizers, those who drank up to 3 cups a day, actually had a lower risk, as much as 52% lower.

So here’s the takeaway:

If you are a slow metabolizer, then drinking more than a cup of coffee a day may be risky for your heart. But a single cup of coffee seems to have no effect on heart risk, regardless of the genome variants. Moderation and self-regulation appear to be key.

Are You Insane, or Just Over-Caffeinated?

Were witches burned at the stake simply because they were over-caffeinated? It’s possible that strange behavior and diagnosed mental disorders have actually been incidents of caffeine intoxication. Nervousness, muscle twitches, rambling speech or thoughts are some symptoms of caffeine intoxication. Mental health professionals see people with these same symptoms all the time, but until recently, they rarely asked patients about their caffeine habits.

Doctors and mental care physicians are now being urged to consider whether curing a person’s mental instability may be as simple as taking them off caffeine.

I wonder how many inmates were sent to the cuckoo’s nest with misdiagnosed mental illness, when they were really suffering the combined effects of too much caffeine and mild mental disorders.

Caffeine’s Good Mood Effects

Mental health is as complex as caffeine, and caffeine can be a boost to some mental health conditions. Scientists have associated caffeine with lifting depression and preventing suicide.

The Caffeine Gene and You

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