The Diet Therapist


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One question I get asked a lot is:

"Is coffee 'bad' for you?"

Posted by The Diet Therapist, 16th Febrary 2017

Addictive “drug” or Black Gold?


Many of us rely on coffee for a quick energy rush before running out the door in the morning, or as a boost to get through the day at work. Increasingly, research has shown that there may be more benefits to a cup of coffee than helping us to feel more awake, including helping to reduce the risk of developing type II diabetes, protect against neurodegenerative diseases, and lower the risk of liver cirrhosis.  But it’s not all rosy; many people suffer from unpleasant side effects when drinking coffee – and there may be some health risks for some individuals.


How do we metabolise coffee?

When we think of coffee, we often think of “caffeine” – the psychoactive compound that naturally occurs in lots of different plant species. When you drink a cup of coffee, caffeine is absorbed quickly into the bloodstream, (within about 45 minutes), and its effects last between 4-6 hours.


Caffeine itself is metabolised by the liver, and broken down into other metabolites (paraxanthine, theophylline, and theobromine – the latter is also found in chocolate).  These compounds are partly responsible for some of the physiological effects that we associate with coffee, for example, its diuretic effect (theobromine relaxes blood vessels and increases urine volume meaning you pee more).


Caffeine exerts most of its familiar effects by blocking adenosine receptors. Adenosine is a neurotransmitter which promotes sleep, so when receptors are blocked you feel awake and alert. However, this causes adenosine to build up in the brain, and you later get a sudden flood of this neurotransmitter which leads to that familiar caffeine “crash.”  As caffeine affects adenosine receptors, it also affects the activity of another important neurotransmitter in the brain, dopamine which is involved in lots of different pathways in the body, including “motivation-reward” pathways in the brain and motor control.


It’s all in your genes…

How quickly caffeine is metabolised, as well as individual sensitivity and tolerance of its effects are genetically variable (and linked to the CYP1A & PDSS2 genes). Sensitivity is thought to be affected by genetics (how we experience the effects of caffeine), but tolerance, (how we respond over time), can be built up as your body adjusts to increased consumption.


More than Caffeine…

Coffee doesn’t just contain caffeine though, it also has compounds such as chlorogenic acid, caffeic acid, chlorogenic acid and cafestol.  These other compounds are important because they are probably implicated in mediating some of the health benefits of coffee – which aren’t found with other caffeine-based drinks (e.g. energy drinks) or tablets.   It is thought that some of these compounds also have antioxidant activity – and may explain some of the health benefits of moderate intake.

Antioxidants, Fibre & Magnesium…

Did you know that coffee is actually one of the top dietary sources of polyphenol antioxidants in the Western World, and is thought to have more antioxidant activity than cocoa and green tea?  The type of beans, the thermal treatment (roasting process) and brewing methods do make a difference here, but there is little agreement about what types of drinks tends to have the greatest antioxidant potential. However, lighter roasting, green coffee beans, and boiled (e.g. Turkish coffee), are thought to have the most antioxidant activity.


Coffee also contains magnesium and fibre (an espresso contains approximately 5% of your recommended daily intake of magnesium & between 1.2g and 3g of soluble fibre depending on cup size (you should aim for about 6-8g of soluble fibre a day).  This doesn’t mean that you should rely on coffee for fibre, or drink it instead of eating a variety of nutrient-dense foods which are also packed with other beneficial compounds! Also, there have been suggestions that caffeine may increase magnesium excretion (in urine) but the amount of this mineral in coffee probably offsets this (there isn’t a lot of research available on this).




Potential Health Benefits


Coffee has been linked to lots of various health benefits. Recently, it has been associated with a lower risk of developing:


TYPE II DIABETES: In the short term, caffeine has been found to decrease insulin sensitivity and impair glucose tolerance, - both of which might contribute to Type 2 diabetes risk.  It is also a nervous system stimulant, so can cause the release of adrenaline which raises heart rate and increases blood sugar…However, longer-term data from cohort and epidemiological studies has suggested that regular moderate coffee consumption (> 4 cups daily) lowers the risk of developing this disease and help maintain normal glucose tolerance.  It’s thought the mechanisms behind this could be related to chlorogenic acid or other compounds in coffee beans.


PARKINSON’S DISEASE: Several case-control studies have suggested that coffee may help to reduce the risk of some neurodegenerative diseases, including Parkinson’s Disease, and a recent meta-analysis suggested that this protection is seen to be strongest with 3 cups a day.  However, the association is stronger in men, and further research is needed on how female hormone therapy might interact with caffeine and affect risk factors for women. 

It’s thought that coffee affects Parkinsons’s risk via its effect on brain pathways (particularly linked to how caffeine binds to adenosine receptors and modulates dopamine activity); this action is also linked to preventing HIAPP amyloid protein formation (amyloid plaques are one of the primary marker of Alzheimer’s disease).


LIVER DISEASE: Some studies have found moderate coffee consumption helps to protect against alcoholic cirrhosis and could potentially protect against liver damage.


MULTIPLE SCLEROSIS:There is some very preliminary animal-based research on whether coffee consumption could potentially decrease the risk of developing MS in humans by suppressing inflammation, but more research is needed to evaluate these claims.


DEPRESSION: A 2011 study found that coffee drinkers had a lower risk of depression, building on earlier research, which suggested that suicide risk is lower among people with a higher consumption of coffee.  However, further research is needed to verify these findings and determine whether caffeine may contribute to the prevention or treatment of depression.



Potential Negative Effects on Health


There are also potentially negative aspects to coffee consumption, and many of these depend on individual sensitivity/tolerance.  If you suddenly stop having your usual coffee you may well experience withdrawal symptoms including headaches, fatigue, drowsiness, low mood, difficulty concentrating, and irritability.  Gradually cutting down on your usual consumption is far less likely to result in these symptoms.


SLEEP DISTURBANCE & ANXIETY: Consuming too much caffeine can lead to heart palpitations, anxiety, a feeling of “jitteriness” and even exacerbate panic attacks.  If you know you are sensitive to caffeine, be careful to limit your consumption.  Many people find consuming caffeine late in the afternoon can affect their sleep patterns and keep them awake – if this applies to you, try not to drink it after 2pm.


PREGNANCY: Excess consumption of coffee in pregnancy is thought to increase the risk of complications and pregnant women should limit intake to 200mg a day or less – the equivalent to 2 mugs of instant coffee.


INCREASED BLOOD PRESSURE: Regular coffee intake does temporarily increase blood pressure, but the effect is thought to be small.  However, other caffeinated drinks and foods (e.g. coca cola and energy drinks) may have different (and potentially negative) effects on BP.


SMOKING:  Nicotine decreases the half-life of caffeine – which means it is cleared from your body quicker. This is important if you are trying to quit smoking, as you may find you are much more sensitive to the effects of caffeine which may affect your tolerance.