There is no doubt about it; we are a nation of coffee lovers. It is estimated that we drink an average of 95 million cups per day in the UK, and that coffee contribute £17.7 billion to the UK economy every year. Second only to water as the world’s leading beverage, it is important to be clear on the risks and benefits to health that coffee confers, especially in such sensationalist times where the daily cup has been purported to be everything from a death sentence to the elixir for eternal life.
So first of all, what exactly is coffee? Derived from coffee beans grown on trees between the Tropics of Cancer and Capricorn, coffee in the form we drink it contains more than 1,000 different compounds. Arguably the most well-known of these is caffeine, but it also contains substances called diterpene alcohols, which are important as they are known to increase cholesterol, and chlorogenic acid, which has antioxidant and anti-inflammatory properties (more on these later). The average caffeine content of a cup of filter coffee is 115-175 mg, while instant coffee contains 65-100 mg, and a word of caution about decaffeinated coffee – it is not always what it says on the tin with some decaf varieties containing up to 35 mg per cup.
In terms of its effect on the cardiovascular system, there are many areas to consider and we will look at blood pressure (hypertension), cholesterol and heart rhythm in turn. To start with blood pressure, many people think that a cup of coffee each day will cause their blood pressure to rise and that they should therefore avoid it. Is this true? Well, yes and no. In “never drinkers” coffee ingestion has been shown to cause a sudden but transient increase in blood pressure, but the long term effects of coffee (and specifically caffeine) on blood pressure in regular drinkers are actually negligible; a large meta-analysis of 10 randomised controlled trials and 5 cohort studies looking at hypertension in coffee consumers concluded that coffee consumption had no clinically important effect on blood pressure or the risk of developing hypertension. Interestingly it is also thought that long term exposure to some of the protective compounds present in coffee might counteract the blood pressure increasing effect of the caffeine it also contains.
So what about the effect on cholesterol? Cafestol and kahweol are two diterpene alcohols found in coffee, and these are known to increase serum cholesterol, and in particular the “bad” LDL cholesterol. The good news, however, is that interestingly the concentration of these compounds depends very much on how the coffee is actually prepared. Diterpenes are extracted from coffee beans by prolonged contact with hot water, and so boiled coffee types, such as those used to create Turkish coffee and French press coffee, are much higher in these compounds than in filtered coffee, where the castefol sticks to the filter paper and does not make its way into the cup. Instant coffee also has lower levels.
And so to heart rhythm. Caffeine is known to induce palpitations, and as such concern has often been raised that coffee might cause abnormal heart rhythms. A 2011 study concluded that people who drank 4 cups of coffee per day actually tended to have fewer cardiac arrhythmias, including less atrial fibrillation, than non-drinkers. Research has also demonstrated that in normal healthy adults caffeine in doses of up to 500 mg per day (equivalent to 4 or 5 small cups of coffee) did not increase the frequency or severity of ventricular arrhythmias either. Some studies have posited that caffeine might even be protective against arrhythmias; the theory being that adenosine, which is secreted naturally within the body and is known to affect cardiac electrical conduction, is inhibited by caffeine, and might thereby reduce the risk of abnormal rhythms. This is a contentious area, however, and the data are not entirely clear in either direction; until more research has been done looking at caffeine ingestion in patients with documented arrhythmia, patients susceptible to palpitations and abnormal rhythms are advised to keep their intake to a minimum.
Coffee is also known to have beneficial effects in other areas of health, for example in reducing the risk of depression, Alzheimer’s disease and Parkinson’s disease. A Harvard study of 20,000 people concluded that regular coffee drinkers have fewer symptoms of asthma, and other studies have shown that it can prevent gallstones and may even be protective against infectious and malignant diseases, particularly of the liver. There is even talk of coffee reducing the risk of ischaemic stroke (where the blood supply to part of the brain is cut off). The mechanism behind this is unknown however, although some researchers suggest that this is due to the anti-inflammatory properties of coffee.
This all sounds very favourable indeed, but before you rush to put the kettle on, coffee does have its negatives. Many people find that it can induce palpitations, tremor, feelings of anxiety and can interfere with sleep. Furthermore the metabolism of certain drugs such as antidepressants, anti-arrhythmics and bronchodilators (inhalers) can be affected by caffeine, and caffeine can also not only increase urine output but also the amount of calcium and magnesium excreted in the urine, which is bad news for bone health (although it is thought that the calcium lost per cup of coffee can be offset by adding 2 teaspoons of milk to each cup, so all is not lost). Caffeine does also create a physical and psychological dependence, although in comparison to other addictive vices such as alcohol and cocaine, the risk to health of such dependence is very low indeed.
One final point of caution is that the flavoured frappuccinos, macchiatos and the like that we buy from places like Starbucks and Costa are often laden with sugar, milk, cream and syrups, such that some large cups contain up to 700 calories and 25g of fat per drink; the health implications of drinking three or four cups of these every day are obviously vast, and so for coffee to be beneficial to health, it is best to drink it filtered with one or two teaspoons of skimmed or semi-skimmed milk and no added sugar.