Coffee is the most popular beverage worldwide, its consumption being second only to that of water. It is thought that 2.25 billion cups are consumed everyday with production in 2016/17 of over 150 million 60kg bags. So, are we doing the right thing, is coffee consumption beneficial or detrimental to our health? There has, in the past, been negative connotations with coffee intake due to its caffeine content which may therefore have an undesirable effect on health. However more recently research has demonstrated multiple health benefits of coffee consumption1,2.
Coffee is a complex mixture of more than 800 volatile compounds, of which caffeine and chlorogenic acids are the most common compounds. The presence of these compounds depends on different variables including the variety of coffee and how it is roasted, brewed and processed. When green coffee beans are roasted under high temperatures, chemical reactions between amino acids and carbohydrates, known as Maillard reactions, create a number of unique components. Additionally, coffee is abundant in polyphenols like chlorogenic acids. The main chlorogenic acid in coffee is 5-caffeoylquinic acid, although others are present in significant quantities. Chlorogenic acids may be transformed into phenolic acids and, subsequently, into colonic metabolites. With extensive conjugation at the level of the intestine and the liver, many different metabolites can be identified in a single cup of coffee. Niacin, and the vitamin B3 precursor trigonellin are also present in coffee2,3.
The diterpene compounds, cafestol and kahweo, which are found in coffee oil have been shown to affect antioxidant activity in cell models and mice models by triggering the upregulation of key antioxidant enzymes2.
The main compound in coffee which has an effect on physiology is caffeine. Caffeine is contained in more than sixty plants and has therefore been thought of as a non-essential minor nutrient for the plant which would have been extremely useful as a pesticide. In fact, caffeine is toxic for several insects and animals, especially herbivores. The half-life time (how quickly it is broken down by the body) of caffeine varies widely among individuals depending on factors such as age, liver function, pregnancy, some concurrent medications, and the level of enzymes in the liver needed for caffeine metabolism.
In healthy adults, caffeine’s half-life time is approximately three to four hours. In women taking oral contraceptives, this is increased to five to ten hours and in pregnant women the half-life time is roughly nine to eleven hours. In infants and young children, it may be longer than in adults2.
In physiology caffeine’s mechanism of action is as an antagonist of adenosine receptors, as it is structurally similar to adenosine. These receptors are widely expressed in the human body and have been implicated in several biological functions, both physiological and pathological. These include cardiac rhythm and circulation, lipolysis, renal blood flow, immune function, sleep regulation, and angiogenesis as well as inflammatory diseases, ischemia-reperfusion, and neurodegenerative disorders. Caffeine can block adenosine’s effects at the low concentration achieved after a single cup of coffee.
Caffeine will be discussed more in relation to specific systems, but it should be noted that both caffeinated and de-caffeinated coffee share some health benefits.2
There have been suggestions that coffee may increase the risk of cardiovascular disease. This is due to two diterpenes in coffee which research has shown elevate cholesterol. The studies suggest that diterpenoids in unfiltered coffee may raise plasma low-density (LDL) cholesterol and lower high-density (HDL) cholesterol. On the other hand, these coffee oils have been shown to possess anti-carcinogenic properties. Diterpenes are retained in part by paper filters but are preserved when coffee is directly prepared by boiling the ground beans1,2.
In addition, some research suggests that caffeine has the ability to raise blood pressure. In people who do not normally drink caffeinated drinks and who are normotensive (have a normal blood pressure) and, particularly in hypertensive individuals, caffeine can increase blood pressure. This increase tends to be limited to non-habitual (caffeine-naïve) coffee drinkers and the acute effects of caffeine are transient1.
Therefore, for a long time coffee was considered to be detrimental to cardiovascular health. However, recent research has demonstrated many protective properties for coffee against cardiovascular disease.
A large prospective study assessed the relationship between coffee and all-cause mortality. The study showed lower mortality rates during follow up in those who consumed generous amounts of coffee on a daily basis. The study reported that drinking two or more cups of coffee per day was associated with a significant reduction in all-cause mortality in women after multivariable adjustment, primarily due to a reduction in cardiovascular mortality. Additionally, a strong trend towards a reduction in all-cause mortality was noted in men consuming two or more cups of coffee daily, although it was not statistically significant. Similar findings were noted with decaffeinated coffee, suggesting an effect from a component other than caffeine2.
In addition, a lot of research supports coffee as a compound which can potentially ameliorate diabetes. Compared with no coffee consumption, six cups per day of coffee was associated with a 33% lower risk of type 2 diabetes. Decaffeinated coffee consumption was associated with the same level of protection as seen for caffeinated coffee. There may be a few mechanisms of action by which coffee is protective for diabetes, these include2:
- Coffee has been shown both to increase insulin secretory responsiveness and insulin sensitivity. It appears to act primarily, if not exclusively, through postprandial (after eating), as opposed to fasting, glucose homeostasis.
- In vivo studies show that chlorogenic acid (a polyphenol found in coffee) inhibited gluconeogenesis by affecting expression and activity of the enzyme glucose-6-phosphatase. It also improved skeletal muscle glucose uptake by increasing expression and translocation of GLUT 4 (a molecule responsible for glucose transportation into cells).
- Polyphenols in coffee stimulate GLP 1, which is an important intestinal hormone that is essential in appetite regulation and activates glucose-induced insulin secretion from pancreatic β-cells. Prolonged activation of the GLP-1 signal has been shown to attenuate diabetes in animals and human subjects.
- A recently published randomised study found that consumption of five cups of coffee per day increases adiponectin, compared with no coffee consumption.21Increased plasma adiponectin concentrations leads to decreased insulin resistance.
- Polyphenols in coffee bean extract may bring an additive effect in decreasing body weight gain and increasing insulin sensitivity
The antioxidant polyphenols have been shown to be protective against the development of many conditions including diabetes and cardiovascular diseases. The mechanisms by which it reduces insulin resistance may also explain its protection of cardiovascular health.
There is also research supporting coffee’s liver protective properties. Some ways in which coffee has an effect on the liver are2:
- Coffee intake of more than two cups per day in patients with pre-existing liver disease is associated with a lower incidence of fibrosis and cirrhosis, lower hepatocellular and carcinoma rates, as well as decreased mortality.
- A strong inverse relationship was demonstrated in patients with alcoholic and non-alcoholic cirrhosis and drinking more than four cups of coffee per day. Additionally, this intake was shown to elevate serum enzyme levels, especially in those who drank large quantities of alcohol.
- It was also reported that consumption of decaffeinated espresso coffee was able to reduce not only liver steatosis but also inflammation and fibrosis in rats.
- Chlorogenic acid seems to be effective in suppressing TCBQ-induced oxidative stress (TCBQ is a metabolite of a widely used wood preservative and an inducer of oxidative stress), therefore possessing a hepatoprotective nature. Additionally, chlorogenic acid reduced liver fibrosis.
Inflammatory Bowel Disease
Coffee may also have a beneficial effect for patients with inflammatory bowel disease2:
- In vitro studies have demonstrated anti-inflammatory effects through the suppression of chemokine gene expression and influencing gene expression of activated human macrophages within the cytokine/chemokine signalling pathway. There was also inhibition of pro-inflammatory cytokines CXCL13 and TNF-α, whereas anti-inflammatory IL10 release from activated macrophages was enhanced by coffee charcoal extracts.
- In vivo studies have demonstrated that coffee intake can reduce bacterial translocation into other organs and pro-inflammatory cytokine production in mice with DSS-induced colitis (i.e. chemically induced colitis).
- Chlorogenic acid also demonstrated inhibition of cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), attenuation of IL-1βand IL-6 along with TNF-α in a dose-dependent manner, and inhibition of NF-κB by chlorogenic acid in a recent mice study. Therefore, it shows anti-inflammatory potential in inflammatory bowel diseases.
There is an inverse relationship with coffee consumption and colon cancer risk. It is thought this may be via diterpenes, which possess antioxidant properties. They have also been shown to reduce the formation of DNA adducts* by several genotoxic carcinogens, including, in particular, ones which are associated with colon cancer. Research suggests that diterpenes can promote the elimination of carcinogens and improve antioxidant status and therefore may be protective for other cancers4.
* DNA adducts are modifications to DNA that result from exposure to carcinogens, they may be measured in normal cells as a biomarker of carcinogen exposure.
Neurodegenerative diseases and cognition
There may be some negative effects of coffee on cognitive health, specifically it may increase anxiety. However, most research has shown that coffee consumption increased anxiety, in a dose‐dependent manner, in males but not in females. The effect was increased with the amount of coffee which was consumed and therefore moderate coffee intake had a marginal effect on anxiety in men. It was also found that decaffeinated coffee intake had no effect on mood or depression; whereas increasing caffeinated coffee consumption is associated with a decreased risk of depression2,5.
Coffee consumption has many benefits on cognitive function and is associated with a decreased risk of neurodegenerative diseases. For example:
- There is an inverse relationship between levels of exposure to caffeine and risk of developing Parkinson’s disease.
- In the CAIDE study, (CV Risk Factors, Aging and Dementia) coffee drinking of three to five cups per day at midlife was associated with a decreased risk of dementia/Alzheimer’s disease (AD) by about 65% at late-life. Participants were followed up at an average of 21 years and demographic, lifestyle and vascular factors, and depressive symptoms were adjusted for.
- The effect of coffee on cognition may be mediated by its antioxidant capacity and its effects on increasing insulin sensitivity.
Exercise and performance enhancing
Meta-analyses of data suggest that caffeine ingestion improves exercise performance in a broad range of exercise tasks. Ergogenic effects of caffeine on muscle endurance, muscle strength, anaerobic power and aerobic endurance were substantiated reviewing many studies. It seems that the magnitude of the effect of caffeine is generally greater for aerobic as compared with anaerobic exercise6.
An indirect but significant benefit of consuming coffee is that it may reduce intake of other beverages which are not beneficial to health such as soft drinks which are high in sugar, carbonation, artificial sweeteners, flavours and colourings.
What is the daily recommended upper limit of caffeine consumption?
Whilst some of the studies quoted above have mentioned benefits being seen with 4 cups or 6 cups of coffee per day, there is a wide variation in the caffeine content of each cup. An instant cup of coffee contains around 80mg of caffeine and some barrista cups of coffee may contain over 300mg per serving.
The European Food Safety Authority’s recommendation is that daily caffeine consumption should not exceed 400mg of caffeine (from all sources), consumed through the day, with a maximum of 200mg in one serving7. Pregnant women are advised to have no more than 200mg through the day. Remember that, due to its long half-life, caffeine consumption after 2pm may disturb both sleep onset and sleep quality.
It can be seen that while there are some downsides to coffee consumption, overall there is a strong association with protection against some chronic diseases. It should also be noted that the majority of the negative research has been seen in very high caffeine consumption and therefore moderate coffee consumption of approximately two to four cups per day has been shown to be largely beneficial to overall health and wellbeing.
It should be noted that some individuals are particularly sensitive to caffeine and high coffee consumption may therefore not be appropriate. In these cases it can still be beneficial to consume decaffeinated coffee which has demonstrated most of the same health benefits (and in some cases additional benefits) to that of caffeinated coffee2,3.
Due to the concern over pesticide residues in coffee and chemicals used in the decaffeination processes, we recommend, where possible, choosing organic brands of caffeinated or decaffeinated coffee; and there are brands that also offer the reassurance of Fair Trade.
- Coffee is the most consumed beverage after water, worldwide.
- Coffee contains a large amount of different chemicals, the most significant of which is caffeine but also chlorogenic acids, diterpenes, niacin, and the vitamin B3 precursor trigonellin.
- Brewing methods affect the chemical properties which are found within coffee.
- Coffee in the past been associated with an increased cardiovascular risk due to its diterpene content which may raise cholesterol. Additionally, caffeine also has the ability to increase blood pressure and anxiety.
- On the other hand, the high polyphenolic content has antioxidant properties and has been shown to be protective for many conditions.
- Coffee consumption is associated with reduced risk of cardiovascular disease, diabetes, liver disease, inflammatory bowel disease and neurodegenerative diseases including Alzheimer’s and Parkinson’s.
- Mechanisms by which coffee is protective include: by improving insulin sensitivity and glucose uptake, anti-inflammatory and anti-oxidant properties, reduction of gene expression associated with some cancers.
- Coffee consumption has also been shown to improve physical performance particularly for aerobic exercise.
- Decaffeinated coffee possesses many of the same health benefits as coffee containing caffeine.
- Moderate coffee consumption of approximately two to four cups per day (not exceeding 400mg of caffeine over the day) has been shown to be largely beneficial to overall health and wellbeing. Pregnant women should limit consumption to 200mg. A cup of instant coffee contains around 80mg. A cup of barrista coffee can contain over 300mg.
- Due to the concern over pesticide residues in coffee and chemicals used in the decaffeination processes, we recommend, where possible, choosing organic brands of caffeinated or decaffeinated coffee; and there are brands that also offer the reassurance of Fair Trade.
If you have questions regarding the topics that have been raised, or any other health matters, please do contact me (Helen) by phone or email at any time.
firstname.lastname@example.org, 01684 310099
Helen Drake and the Cytoplan Editorial Team
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- Gökcen BB, Şanlier N. Coffee consumption and disease correlations. Crit Rev Food Sci Nutr. 2019;59(2):336-348. doi:10.1080/10408398.2017.1369391
- Nieber K. The Impact of Coffee on Health. Planta Med. 2017;83(16):1256-1263. doi:10.1055/s-0043-115007
- Ludwig IA, Clifford MN, Lean MEJ, Ashihara H, Crozier A. Coffee: biochemistry and potential impact on health. Food Funct. 2014;5(8):1695-1717. doi:10.1039/C4FO00042K
- Sartini M, Bragazzi NL, Spagnolo AM, et al. Coffee Consumption and Risk of Colorectal Cancer: A Systematic Review and Meta-Analysis of Prospective Studies. Nutrients. 2019;11(3). doi:10.3390/nu11030694
- Patil H, Lavie CJ, O’Keefe JH. Cuppa joe: friend or foe? Effects of chronic coffee consumption on cardiovascular and brain health. Mo Med. 2011;108(6):431-438. http://www.ncbi.nlm.nih.gov/pubmed/22338737. Accessed September 17, 2019.
- Pickering C, Grgic J. Caffeine and Exercise: What Next? Sport Med. 2019;49(7):1007-1030. doi:10.1007/s40279-019-01101-0
- https://efsa.onlinelibrary.wiley.com/doi/epdf/10.2903/j.efsa.2015.4102. Accessed 17.09.19