What is caffeine, and does it cause cancer?

Quick Answer
An alkaloid stimulant found naturally in coffee, tea, cocoa, and many carbonated drinks.
Expert Answers
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Related cancers: Skin cancer, breast cancer, colon cancer, rectal cancer, bladder cancer, kidney cancer, ovarian cancer, pancreatic cancer

Delivery routes: Caffeine is most often ingested as a stimulant in coffee, tea, cocoa, chocolate, soft drinks, and energy drinks. Caffeine tablets are also taken orally as a stimulant. Caffeine is also an ingredient in certain nonprescription drugs designed to address colds, flu, headache, and pain, as well as preparations that function as stimulants to allow users to stay awake.

How this drug works: Caffeine acts as a stimulant because it inhibits neurotransmitters that normally act as depressants. Specifically, caffeine occupies the neuron’s receptor sites for adenosine, which is a neuron inhibitor. Instead of being blocked and inhibited, the neuron remains active, thereby increasing neuron activity.

Despite numerous studies, the relationships between caffeine intake and cancer risk remain inconclusive at best and contradictory at worst. Some studies show an inverse relationship between caffeine intake and cancer risk, while other studies suggest that caffeine increases the risk of certain cancers.

Links between caffeine and cancer risk are based on the suggestion that caffeine and some of its metabolites can cause changes in cell reproduction that might enhance growth and proliferation, thereby increasing the growth and spread of cancerous cells that develop.

Alternatively, other studies have suggested that caffeine and a related molecule called theophylline can block production of an enzyme that is crucial for cell growth, thereby inhibiting tumor proliferation. Studies at Rutgers University demonstrated that hairless mice treated with caffeine showed much greater resistance to skin tumors than untreated mice, but the experiment has yet to be conducted on human volunteers.

Possibly the greatest concern is about a possible relationship between caffeine consumption and breast cancer incidence, with some studies suggesting that a combination of caffeine and methylxanthines showed positive correlation to breast cancer and other diseases of the mammary glands. For example, caffeine and methylxanthines (also found in coffee and tea) are associated with increased severity of fibrocystic breast disease, which may lead to the development of breast cancer, but this finding is contradicted by other studies, leading the American Cancer Institute to announce that there is no evidence between breast cancer and caffeine intake at any level.

Although numerous studies have suggested a causal relationship between coffee intake and pancreatic cancer, none so far has provided conclusive support.

The relationship between caffeine and cancer is complex and remains unproven; both the International Agency for Research on Cancer (in 2007) and the American Cancer Society have concluded that there is no evidence that caffeine is carcinogenic. This verdict is echoed by the World Health Organization (WHO) and the Food and Drug Administration (FDA). In 2012, the American Institute for Cancer Research reported that the American Journal of Clinical Nutrition had published a European study that found coffee (both caffeinated and decaffeinated) was not associated with cancer risk and overall risk of cardiovascular disease.

Side effects: In the short term caffeine increases attention span and simultaneously decreases the feeling of tiredness and weariness. Caffeine intake in children may cause hyperactive behavior. Caffeine can offset some of the effects of alcohol, but performance and coordination remain unaffected. Caffeine also increases plasma levels of fatty acids, cortisol, and epinephrine.

Negative effects of excessive caffeine consumption vary with age, diet, and exercise levels. Generally, higher caffeine intake may elevate blood levels of sugars and fats, increase blood pressure, irritate the lining of the stomach, and cause heartburn, irregular heartbeat, irritability, nervousness, anxiety, depression, insomnia, and the disruption of sleeping habits.

Excessive caffeine intake has also been linked to stroke and heart attack. The relationship between caffeine intake and heart problems is of great concern. Recent studies by the Adventist Health Study group reported finding a 50 percent increase in risk of serious heart disease, including heart palpitations and cardiac arrhythmias, both of which can lead to heart attacks. Other studies, however, have failed to demonstrate any relationship between coronary heart disease, stroke, and caffeine intake.

Some researchers have also suggested a relationship between caffeine doses and the severity and duration of premenopausal syndrome (PMS) in females among heavy consumers of coffee, tea, and other fluids containing caffeine.

Other studies have linked higher-than-normal caffeine consumption with lowered rates of conception, birth defects, retarded fetal growth, reduced birth weight, spontaneous abortion, premature delivery, and stillbirth. There is some evidence that caffeine intake by males prior to mating may result in significant fetal growth retardation, but this too remains problematic and awaits further study. While none of these claims is absolute, women are advised not to consume caffeine while pregnant or planning on becoming pregnant, since blood levels of caffeine can be transferred through the placenta and can be metabolized by a developing fetus.

Finally, high caffeine intake reduces the absorption of dietary iron by 40 to 60 percent and reduces calcium intake while simultaneously increasing the rate of calcium loss, all of which may lead to serious calcium imbalance in blood and body fluid levels.

Bibliography

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