Caffeine and cancer

ATC CODE: N06BC01

ALSO KNOWN AS: Trimethylxanthine, coffeine, theine, mateine, guaranine, methyltheobromine

DEFINITION: Often considered the most widely used drug in the world, caffeine is an alkaloid stimulant found naturally in coffee, tea, cocoa, and many carbonated drinks. Caffeine is a secondary metabolite substance that plants manufacture as a pesticide against insects and other invertebrates. Humans use the naturally bitter caffeine as a stimulant. Coffee, tea, and cocoa have become extraordinarily popular worldwide. In the United States, for example, it is estimated that 80 percent of adults drink either coffee or tea, and over 70 percent of adults and children consume soft drinks that contain caffeine. Different studies support contrasting positions on caffeine's correlation as a cause of cancer.

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. It is also taken orally as a tablet. Caffeine is an ingredient in certain nonprescription drugs designed to address colds, flu, headaches, 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 generally act as depressants. Specifically, Caffeine occupies the neuron's receptor sites for adenosine, 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. 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 hypothesis that caffeine and some of its metabolites 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 the production of an enzyme 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. Still, the experiment has yet to be conducted on human volunteers.

The most significant concern about caffeine is suggestions of a possible relationship between its consumption and the incidence of breast cancer. Some studies suggest that a combination of caffeine and methylxanthines showed a 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. Other studies nonetheless contradict this finding. This has led 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. Dating back to 2007, the International Agency for Research on Cancer concluded that there was no evidence that caffeine was carcinogenic. This viewpoint was supported by the World Health Organization (WHO) and the Food and Drug Administration (FDA). The American Institute for Cancer Research reported that the American Journal of Clinical Nutrition found that caffeinated and decaffeinated coffee was not associated with cancer risk and overall risk of cardiovascular disease. More than a decade later, this consensus remained. In 2018, the American Cancer Society published an article casting doubt on the caffeine/cancer linkage. Furthermore, the article stated that many cancer-causing activities falsely linked to caffeine stemmed from other behaviors, such as smoking. This was because many smokers were also coffee drinkers. In a 2021 article published in both Medical Principles and Practice and also the National Library of Medicine, data indicated coffee consumption actually reduced cancer risk.

Side effects: In the short term, caffeine increases attention span and simultaneously decreases feelings of fatigue. 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.

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

Excessive caffeine intake has been linked to stroke and heart attack. The relationship between caffeine intake and heart problems is of great concern. 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 researchers have linked higher-than-normal caffeine consumption with lowered rates of conception, congenital disabilities, 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 conclusion remains problematic and awaits further study. While none of these claims is absolute, women are advised not to consume caffeine while pregnant or intending to become pregnant. This is because blood levels of caffeine can be transferred through the placenta and can be metabolized by a developing fetus.

Last, high caffeine intake reduces the absorption of dietary iron by 40 to 60 percent and reduces calcium intake. This occurs simultaneously with an increase in the rate of calcium loss, all of which may lead to severe calcium imbalance in blood and body fluid levels.

By the mid-2020s, linkages between caffeine consumption and cancer remained dubious. Many in the medical community continued to raise concerns about caffeine but focused their messages on the dangers of its side effects. The trend was now to advocate caffeine consumption in moderation.

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