Caffeine is mostly known as a stimulating anti-sleep compound and energy-booster.
As a result of years of studies, researchers have found caffeine’s possible link to numerous pharmacological and physiological effects. These include cardiovascular, respiratory, renal, and smooth muscle effects, as well as effects on mood, memory, alertness, and physical and cognitive performance (1).
Caffeine has been the beverage of choice many reach for to get them going each morning. It has also long been the subject of great debate with some warning of its dangers and others touting its benefits. There is a growing body of evidence, however, pointing to the latter.
In 2016, the World Health Organization officially removed coffee from the list of potentially carcinogenic foods (2).
Caffeine’s action is believed to be mediated through several mechanisms: the antagonism of adenosine receptors, the inhibition of phosphodiesterase, the release of calcium from intracellular stores and antagonism of benzodiazepine receptors (3).
Caffeine is found in numerous sources, such as coffee, tea, soft drinks, chocolate and certain medications, including appetite suppressants, diuretics, analgesics and decongestants.
Caffeine may play a potential positive role in cardiovascular health. Preliminary research presented at the American Heart Association’s Scientific Sessions in 2017 showed that drinking coffee may be associated with a decreased risk of developing heart failure by 7 percent and stroke by 8 percent with every additional cup of coffee consumed per week compared with non-coffee drinkers (4).
It is important to note that this information was gathered using machine learning to analyze data from the long-running Framingham Heart Study, which includes information about what people eat and their cardiovascular health.
Machine learning is the practice of using algorithms to analyze data and find associations within the data.
Researchers also used traditional analysis in two studies with similar sets of data — the Cardiovascular Heart Study and the Atherosclerosis Risk In Communities Study. Many in the medical community are hopeful that machine learning could help them identify additional factors to improve existing risk assessment models.
In a Japanese study, it was found that participants who drank a cup of caffeinated coffee had a 30 percent increase in blood flow over 75 minutes compared to those who drank decaffeinated coffee.
While it is still unclear how caffeine improves small blood vessel function, researchers believed that caffeine reduces inflammation and helps open blood vessels (5).
Caffeine has a positive effect on memory. A team of scientists at Johns Hopkins University found that caffeine has a positive effect on long-term memory. They conducted a double-blind trial in participants who did not regularly eat or drink caffeinated products. Participants received either a placebo or a 200-milligram caffeine tablet five minutes after studying a series of images.
Their caffeine levels were measured by salivary samples.
The next day, both groups were tested on their ability to recognize images from the previous day’s study session. On the test, some of the visuals were the same as those from the day before, some were new additions and some were similar but not the same.
It was concluded that more members of the caffeine group were able to correctly distinguish the new images as “similar” to previously viewed images rather than erroneously citing them as the same (6).
Coffee may decrease risk of depression in women. Many animal and human studies document the alertness and energy-boosting effects of caffeine, but the studies have all been short-term studies. A group of researchers from Harvard School of Public Health set out to investigate the long-term effects of caffeine on depression.
The results showed that women who drank two to three cups of caffeinated coffee a day were 15 percent less likely to develop depression over the 10-year study period, compared with women who drank one cup or less per day. Women who drank four or more cups of coffee a day had a 20 percent lower risk.
Women who drank decaf didn’t show a similar reduction in depression rates (7).
Researchers warn, however, that too much caffeine can increase anxiety which can contribute to depression.
While experts are not exactly sure how caffeine affects mood, they believe caffeine may protect neurons lost to neurodegenerative disease.
Caffeine improves exercise performance and endurance. There are several studies showing a promising link between caffeine and improving exercise performance and endurance. A study published in the Aviation, Space, and Environmental Medicine examined the effects of caffeine on vigilance, marksmanship and run performance during a period of 27 hours without any sleep in Special Forces personnel.
Thirty-one soldiers were divided into caffeine and placebo groups. Throughout the testing time period, they performed various physical exercises including running and underwent marksmanship and vigilance testing, and performed a control observation and reconnaissance vigilance task as well as a live-fire simunitions exercise.
The results of the study conclusively showed the benefits of caffeine for maintaining vigilance and reaction time during an overnight period of sleep deprivation. There was also either no change or a positive impact on marksmanship reported (8).
In another study, researchers used a treadmill to study the effects of the ingestion of caffeinated coffee on: the time taken to run 1500 m; the selected speed with which athletes completed a 1-min ‘finishing burst’ at the end of a high-intensity run; and respiratory factors, perceived exertion and blood lactate levels during a high intensity 1500-m run.
The results showed that consumption of caffeinated coffee could enhance the performance of sustained high-intensity exercise. Specifically, ingestion of caffeinated coffee decreased the time taken to run 1500 m; increased the speed of the ‘finishing burst’; and increased VO2 (the measurement of the maximum amount of oxygen that an individual can utilize during intense exercise) during the high-intensity 1500-m run (9).
Yet another study concluded that physically active men experienced a 1.4 percent reduction in fastest sprinting speed after ingesting a caffeine gelatin capsule (10).
Caffeine appears to have the most benefit, however, on trained athletes rather than beginners.
In a sprint performance in trained and untrained swimmers, it was determined that only trained subjects exhibited significant improvement in their swimming velocity after caffeine consumption (11).
In two studies, caffeine showed no effect in the performance of recreationally active men undergoing an anaerobic exercise test (12,13). Yet, in a study including competitive athletes undergoing a similar test, caffeine consumption resulted in a significant improvement in power (14).
Caffeine may lower the risk of some cancers. According to the American Cancer Society, recent studies show that coffee consumption appears to lower the risk of prostate cancer, liver cancer, endometrial cancer and some cancers of the mouth and throat (15). The University of Texas MD Anderson Cancer Center also points to a link between caffeine and protection from basal cell carcinoma (skin cancer) 16.
Caffeine linked to a lower risk of endometrial cancer. According to the American Cancer Society, endometrial cancer is the most common cancer of the female reproductive organs (17).
In a study published in Cancer Epidemiology, Biomarkers & Prevention, researchers found that women who drank about three cups of coffee per day appeared to have a 19 percent lower risk for developing endometrial cancer compared with those who drank less than a cup each day (18).
Researchers stress that many more studies are needed to try to isolate the components of coffee that may be responsible for any influence on endometrial cancer.
Coffee consumption decreases the risk of developing type 2 diabetes. According to a 2014 study led by Harvard School of Public Health researchers, people who increased the amount of coffee they drank each day by more than one cup over a four-year period, had an 11 percent lower risk for type 2 diabetes than those who made no changes to their coffee consumption.
Conversely, people who lowered their consumption of coffee by more than one cup a day increased their risk of developing type 2 diabetes by 17 percent (19).
Caffeine may play a role in preventing liver fibrosis and cirrhosis. In an article published in a 2018 issue of Gene Expression – The Journal of Liver Research, the author discusses the revelation that coffee consumption may help prevent the progression of liver fibrosis to cirrhosis and possibly hepatocellular carcinoma.
The author made the following observations based on his review of several retrospective studies investigating associations between coffee consumption and changes in liver enzymes, liver fibrosis, and hepatocellular carcinoma in patients with a variety of chronic liver diseases.
Coffee consumption is inversely related with changes in liver enzymes, liver fibrosis and hepatocellular carcinoma in patients with chronic liver disease and the response is dose dependent.
The strongest inverse association between coffee consumption and progression of liver fibrosis in patients with chronic disease occurs when individuals drink two to four cups of drip coffee per day (20).
Caffeine may help burn fat. While there is no concrete evidence that caffeine consumption results in significant or permanent weight loss, it may slightly boost weight loss, according to the Mayo Clinic.
There are two theories on how caffeine can help keep the pounds off; one: caffeine may temporarily reduce feelings of hunger and two: caffeine stimulates thermogenesis (think: thermogenics) — one way your body generates heat and energy from digesting food and appears to increase energy use even when at rest (21).
One of the main drawbacks is that these results tend to be temporary as people become tolerant to the effects of regularly consuming caffeine (22). Therefore, relying on coffee and other caffeinated beverages may be an ineffective weight-loss strategy in the long run.
Cycling your coffee drinking — drinking coffee for two weeks and then taking a break for two weeks may help to prevent a buildup of caffeine tolerance.
Heavy consumption of caffeine (typically more than four cups) can cause such side effects as migraine headaches, insomnia, nervousness, irritability, restlessness, stomach upset, fast heartbeat and muscle tremors (23).
Some people are more sensitive to caffeine than others. Certain factors including genetics, body mass, age, medications and health conditions, such as anxiety disorders, make some more sensitive to its negative effects (24).
According to MedlinePlus – Health Information from the National Library of Medicine, those who should limit or avoid caffeine include those who are pregnant or breastfeeding, those who suffer from migraines or insomnia, have anxiety, ulcers, fast or irregular heart rhythms or have high blood pressure (25).
Caffeine intake should be tailored to individuals.
For healthy adults, up to 400 mg per day is considered safe. Those who do not normally consume caffeine should start with a lower amount. While amounts over 400 mg have been shown in studies to have a performance-enhancing effect, the studies were typically short term. In addition, higher dosages are linked to unwanted side effects.
Medical experts also warn that adding cream and sugar to coffee adds fat and calories. It is important to keep this in mind especially if you drink several cups each day.
Individuals with a history of high blood pressure or cardiovascular problems should consult with their treating physician before drinking caffeinated beverages.
Caffeine can be supplemented through beverages, like coffee or tea, or taken in a pill form.
The amount of caffeine in different types of drinks can vary. According to MedlinePlus, an 8-ounce cup of coffee contains 95-200 mg of caffeine; a 12-ounce can of cola contains 35-45 mg; an 8-ounce energy drink contains 70-100 mg; and an 8-ounce cup of tea contains 14-60 mg (26).
There are several factors that can affect caffeine content, including the origin of the beans, processing and preparation method and brewing time. When it comes to brewing method, drip coffee has the highest caffeine content at approximately 115-175 mg, while instant coffee has the lowest with about 30 to 90 mg (27,28).
Coffee is a stimulatory compound that can make you feel more awake and give you a boost of energy. After years of studies, researchers have found caffeine’s possible link to numerous pharmacological and physiological effects. Such benefits include improving cardiovascular health and long-term memory, decreasing the risk of depression in women, lowering the risk of certain cancers and type 2 diabetes and improving the physical performance of trained athletes.
There is also some evidence pointing to caffeine’s ability to help burn fat and prevent liver fibrosis and cirrhosis.
Caffeine has long been a popular topic of debate, with some warning of its dangers and others touting its benefits. While many more studies are needed, modern research shows that moderate consumption of caffeine may actually do more good than harm.
Consuming up to 400 mg per day is considered safe for healthy adults.