This article was written by our regular contributor; dietitian – Maeve Hanan.
Coffee is one of the most popular drinks in the world, so it’s unsurprising that the health impact of this drink gains a lot of attention. This article will explain the benefits and drawbacks related to drinking coffee.
The Caffeine Content of Coffee
A big factor when it comes to the impact of coffee is it’s caffeine content. An average 200ml cup of coffee contains ~90mg of caffeine, although this can vary depending on how it has been made and the type of coffee bean used (1). In fact, a study comparing the caffeine content of a variety of coffee drinks from 6 different shops found that the caffeine content ranged from 58-259mg per drink, and interestingly this varied widely from 259–564mg for the same type of coffee from the same shop when this was checked for six days in a row (2).
The European Food Safety Authority (EFSA) recommend that consuming upto 400mg of coffee per day and upto 200mg in one serving is safe for most healthy adults, with the exception of pregnant and breastfeeding women who are advised to consume no more than 200mg of caffeine per day (2, 3).
However, there is a lot of variation in the way that different people metabolise and react to caffeine, related to genetics, body size, liver health, age etc. (4). For example, it seems that older adults may be more sensitive to caffeine than younger adults overall.
It’s important to remember that caffeine is also found in tea (including green tea), cola, energy drinks, chocolate, as well as certain medication and sports supplements.
What About Decaf Coffee?
Decaffeinated (decaf) coffee can be produced by a variety of methods such as soaking coffee beans in solvents or water, using CO2 or oils prior to roasting the beans. In Europe decaf coffee must contain less than 0.3 % caffeine (dry weight), and in the US the regulation is less than 0.1% caffeine (dry weight) (5, 6). However, studies have found that this can range from 0-18mg depending on the brand or coffee shop (2, 7).
Although further research is needed, decaf coffee appears to provide similar health protective benefits as caffeinated coffee due the antioxidants it provides (9, 9).
As decaf coffee contains little to no caffeine, both the benefits and drawbacks related to caffeine (as discussed below) don’t apply. So decaf coffee is a good option for those who are sensitive to caffeine or who need to limit their intake – but enjoy the taste!
The Benefits of Drinking Coffee
Source of antioxidants
Both caffeinated and decaf coffee are a good source of antioxidants and polyphenols (beneficial plant compounds) such as hydroxycinnamic acids and flavonoids (10). Many of coffee’s health benefits are thought to be related to these compounds.Coffee also contains small amounts of certain B-vitamins and minerals like potassium and manganese (11).
Counts towards your fluid intake
Although the caffeine in coffee can increase urine production, consuming upto 400mg of caffeine per day has not been found to have a dehydrating effect (12). Therefore, drinking coffee counts towards our daily fluid intake, and consuming enough fluid is vital for a number of body functions including concentration, temperature regulation, heart, gut and kidney health (13).
Improves alertness and mental performance
There is strong evidence that improvements in alertness, attention and mental performance occur when at least 75mg of caffeine (roughly one small cup of coffee) is consumed (14).
Improves endurance performance
Consuming at least 3mg of caffeine per kg body weight one hour before exercise improves endurance performance and capacity (16). Similarly, at least 4mg of caffeine per kg body weight one hour before exercise reduces perceived effort during exercise (15).
Helps with constipation
Coffee is also known to stimulate bowel movements, which may be helpful for those who experience constipation. The evidence related to this is sparse overall and recent studies have also started to investigate the impact of coffee on the gut-brain axis (16).
Lower risk of certain diseases and death
A regular moderate consumption of coffee (often defined as 3-5 cups per day) is also associated with a lower risk of a number of diseases, such as (17, 18, 19, 20, 21, 22):
- Heart disease
- Type 2 diabetes
- Liver cancer (and potentially some other types of cancer too)
- Non-alcoholic liver disease
There is also a possible protective link between drinking coffee and the risk of Dementia and Alzhemiers, but more research is needed (23).
Coffee lovers will also be glad to hear that 3 to 4 cups per day has been linked with a lower risk of overall death (22, 24).
Drawbacks of Drinking Coffee
Impacts sleep quality and quantity
One of the biggest downsides related to coffee is the impact this can have on sleep due to its caffeine content. Consuming even 1-2 espressos 16 hours before bed has been linked with lower quality sleep for those who are more sensitive to caffeine, including older adults (25). Similarly, drinking 400mg of caffeine 6 hours before bed may delay sleep by more than an hour (26). Although we feel the effects of caffeine within 15 – 30 minutes, this can stay in the system for a long time. The average half life (i.e. the amount of time it takes for the body to get rid of 50% of the caffeine) is around 4 hours, although this can vary between 2-8 hours (1, 27). Therefore, it is usually advised to avoid caffeinated drinks like coffee for at least 6 hours before bed, although 8-12 hours is sometimes advised (28). Mid-morning seems to be a good time to drink coffee, as this is both far away from bedtime and not too close to waking when cortisol levels are high (29, 30).
Reduces iron absorption
Another consideration when it comes to timing is that some of the polyphenols (like tannins) found in coffee can reduce iron absorption by as much as 60 – 90% (31, 32). For this reason it is best to leave a 1-hour gap between iron-containing meals and a cup of coffee.
May trigger anxiety
Caffeine can trigger anxiety, especially in those who are more sensitive to caffeine and also when more than 400mg per day is consumed (33). The European food safety Authority (EFSA) caution that children may experience irritability, anxiety or nervousness if they consume 5mg or more caffeine per kg body weight (14).
Can be addictive
Caffeine can also be addictive, infact caffeine withdrawal is now listed as a disorder by both the World Health Organisation and the American Psychiatric Association (34, 35). Withdrawal symptoms from caffeine, such as headaches, mood swings and fatigue, have been seen to occur within 12-24 hours of caffeine avoidance and to last for up to 9 days (36, 37).
Increases urine production
Although drinking coffee is unlikely to be dehydrating, caffeine can increase the production of urine. Therefore, the NHS and National Institute for Clinical Excellence (NICE) recommend that those with urinary incontinence reduce their caffeine intake (38, 39).
Can trigger gut symptoms + reflux
As discussed above, coffee stimulates gut movement. However, for some people this stimulation can trigger gut irritation and diarrhoea; especially for those with IBS (40, 41). Coffee has also been seen to trigger stomach acid secretion, which may impact those who suffer with reflux or heartburn; but studies related to this are conflicted and lacking overall (42, 43).
May increase fracture risk
Consuming a high intake of caffeine (i.e. more than 400mg per day) has been associated with an increased fracture risk (44, 45). This may be related to increased calcium losses from the body and interaction with vitamin D for those with certain genetics. But this evidence is mixed overall, and is unlikely to be an issue for those who consume a good intake of calcium and less than 400mg of caffeine per day (46).
Can increase blood pressure and blood glucose
Caffeine can also increase blood pressure (at least in the short-term) so excessive caffeine intake is discouraged for those with high blood pressure (47, 48). So the NHS recommends drinking no more than 4 cups of coffee per day to improve blood pressure (49). However, as discussed above, overall coffee intake is associated with improvements in heart health and a reduction in the risk of heart disease (1, 50)
Similarly, blood glucose levels may increase in response to caffeine a few hours after drinking a cup of coffee, but glucose response is seen to improve after a few weeks of drinking caffeinated coffee (51).
Caffeine (>200mg) not advised in pregnancy and breastfeeding
Pregnant women are advised to limit their caffeine intake to 200mg as a high intake of caffeine can harm an unborn baby by stunting growth and increasing the risk of preterm birth and miscarriage (1, 52). Breastfeeding women are also advised to stick with the 200mg per day limit because caffeine can pass to the baby and lead to restlessness and sleep issues (53). See here for more information from the NHS about limiting caffeine intake in pregnancy.
There are a number of pros and cons related to drinking both caffeinated and decaf coffee. For most adults, drinking 3-4 cups per day is associated with health benefits including a lower risk of certain diseases and a longer life. It is important not to drink caffeinated coffee close to bedtime and to leave roughly an hour between high-iron foods and coffee. However, our tolerance to caffeine is very individual so those who are more sensitive in terms of anxiety, gut symptoms or sleep issues may need to limit their intake further or opt for decaf. It is important to note that pregnant or breastfeeding are advised to limit their intake of caffeine to 200mg per day.
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