As well as being the top selling hot drink in the world, coffee is considered one of the healthiest (1,2). But what does the evidence say? Is coffee really beneficial to our health? Or are there any negative effects to consuming this beloved drink? Let’s spill the beans…
Chronic disease
The case for drinking coffee is stronger than ever. Evidence suggests that consuming 3-4 cups of coffee per day can have beneficial effects on our health.
Specifically, population studies have found 3-4 cups of coffee to be associated with a reduced risk of cardiovascular and digestive disease (3), liver cancer and cirrhosis (4), type 2 diabetes (5), and depression (6). When it comes to overall mortality, coffee also appears to have what is called a ‘J-shaped association’, meaning the consumption of 1-2 cups per day correlates with lowest risk of mortality, and anything less than 1 cup or more than 4 cups per day correlates with increased mortality risk (7).
*It is worth noting that these studies are correlation studies, and so they cannot prove cause-and-effect. For example, it may be that individuals who drink more coffee, also happen to be more physically active (confounding factors), therefore contributing to the positive effects seen in their findings.
Polyphenols
Both caffeinated and decaffeinated coffee are associated with the above mentioned health benefits, giving rise to the consensus that they are the result of coffee’s rich polyphenol content (molecules that have antioxidant properties). One double espresso, for example, has been shown to have six times more antioxidants than green tea (8).
In addition to lowering risk of heart disease, polyphenols have been associated with:
– Protecting skin from oxidative stress caused by sunlight and pollution (9).
– Reduced risk of cancer due to the polyphenol’s antioxidant and anti-inflammatory properties (10).
– Growth of healthy gut bacteria (11,12).
– Improved memory and learning through boosting blood flow to the brain (13).
Enhancing performance
One cup of coffee contains around 100mg of caffeine; a compound that can boost alertness by stimulating the central nervous system and blocking the neurotransmitter adenosine, which promotes sleep drive (14).
Caffeine from coffee has also been shown to increase glucose metabolism (the rate at which we convert glucose into energy) and muscle glycogen re-synthesis post-exercise (the recovery and replenishment of glycogen stores within our muscle cells) (15). Unfortunately, however, as this is a new area of research, the mechanisms through which caffeine has such metabolic effects are not yet well-established.
Nevertheless, for these reasons, coffee may enhance athletic performance if consumed prior to a high intensity workout. One randomised controlled trial found runners who consumed coffee shaved around 6 seconds off their mile (16), and a similar study found weightlifters’ total load lifted increased by roughly 272kg (reps x sets x weight) following coffee consumption (17).
Tip:
The caffeine found in coffee varies considerably, especially between countries. As a rough guide see below. If you’re looking to enhance performance, consider opting for freshly ground black coffee.
Caffeine content of coffee-based drinks (18)
Black coffee – 95 to 165 mg
Instant black coffee – 63 mg
Latte – 63 to 126 mg (make it vegan by using a plant-based milk such as almond milk or soy milk instead of dairy milk)
Decaffeinated coffee – 2 to 5 mg
Despite the benefits, there are some circumstances in which coffee consumption may be worth reviewing.
Hypertension & heart disease
Not everyone breaks down caffeine at the same rate – some people are considered ‘fast metabolisers’ and some ‘slow metabolisers’.
Evidence suggests that adrenaline levels in the blood only spike for slow metabolisers (19), and that slow metabolisers who exceed 3 cups of caffeinated coffee a day may have an increased risk of hypertension and heart attacks (20,21). Fast metabolisers, on the other hand can break down caffeine so fast that they experience no increase in adrenaline or risk of hypertension, even at 4+ cups of coffee a day (22). It seems that fast metabolisers bypass the negative effects of caffeine, allowing them to gain only the beneficial polyphenols from coffee that work to lower blood pressure, in turn cutting their chance of a heart attack by more than half (23).
Genetic testing can determine if you are a fast or slow caffeine metaboliser (24). However, an easier and cheaper way of determining this is by simply monitoring your symptoms following coffee consumption. Slow metabolisers might find they are jittery or anxious relatively soon following a coffee, or struggle to fall asleep even if their last coffee was in the morning. Fast metabolisers typically won’t experience any of these symptoms, even after multiple coffees (25).
Poor sleep
As mentioned, caffeine’s primary effect on the body is blocking the action of adenosine. Through blocking adenosine, the brain is unable to detect adenosine’s presence and thus it continues to release chemicals that keep us awake (26). As with heart health, sleep is more likely to be impacted amongst slow caffeine metabolisers.
Tip:
Sleep is extremely important for our health, and coffee has an average half-life of 5 hours (meaning the caffeine will still be in your system up to 5 hours after consumption) (27). To optimise sleep, try having a cut off time for caffeinated coffee consumption in the early afternoon, and opt for de-caffeinated options thereafter.
Worsened anxiety and Irritable Bowel Syndrome (IBS)
Being a stimulant, caffeine increases our stress hormones and kickstarts many of our bodily functions, including our digestive and nervous system. If you suffer with diarrhoea-predominant IBS or anxiety, some people, especially slow caffeine metabolisers, may find caffeinated coffee triggers or worsens their symptoms (28). If this is you, consider reducing or eliminating caffeine and see how you feel.
Withdrawal symptoms
Should you decide that reducing or eliminating your consumption of caffeine is the right thing for you and your health, be mindful that you may experience withdrawal symptoms. These can include headaches, decreased energy levels or fatigue, drowsiness, depressed mood, anxiety, difficulty concentrating, and irritability (35). Here are a few tips to reduce the chances and/or severity of these symptoms:
Alongside a plant based diet, coffee consumption can offer a number of health perks, including reduced risk of certain chronic diseases and enhanced mental and physical performance. However, for certain population groups, coffee’s consumption can come with its consequences, requiring some consideration on an individual basis regarding the quantity and timing of consumption. In instances where a reduced caffeine consumption may be beneficial, withdrawal symptoms need to be considered and well managed.
Written by Amber Woodhouse RD for Rosemary Nutrition & Dietetics. Reviewed by Rosemary Martin RD
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