Dementia is the term used to describe a range of conditions which all involve the gradual decline in cognitive functioning. The number of people affected by dementia in an ageing population is rising. In 2010 over 24 million people worldwide were thought to be suffering, and this number was predicted to double every 20 years . Alzheimer’s Disease is the most common and well-known form of dementia, although dementia can be caused by a range of different problems in the brain. Many research studies include patients with all types of dementia, as reaching a specific diagnosis is often difficult and may only become obvious late-on in the disease progression.
All forms of dementia are extremely distressing for patient, carers and clinicians. A lot of interest is focused on searching for so-called ‘modifiable’ risk factors for dementia; things over which we have some control which might influence our chances of developing the condition later in life. Coffee and caffeine consumption is one of these factors.
Caffeine consumption worldwide:
Drinking coffee seems to be coming ever more popular, with branches of familiar coffee chains appearing in every town. Data suggests that the Scandinavians have the highest caffeine consumption, with Finland topping the chart at 12 kg coffee per person per year. The US comes somewhere around 20th with an annual consumption of around 3 - 4kg per person .
Of course, the amount of caffeine consumed depends on how the cup is made, as well the type of bean used, so it is difficult to be completely accurate how much caffeine people are drinking. In general, researchers ask how many cups of coffee are drunk each day, and use this as an estimate of caffeine consumption.
Effects of coffee in the short- and long-term:
Most of us will recognise the short-term effects of drinking a cup of coffee. It increases alertness, and many people feel it helps them to concentrate better. These short-term effects are one of the reasons for coffee’s growing popularity, and the reason some of us reach for a cup in the morning. If we drink too much, coffee can have more unwelcome effects. Taken to excess it can lead to anxiety, high blood pressure and sleep disturbances .
All of these are short-term influences. Much less is known about the effects on our body or repeated coffee drinking over the longer-term. One area of interest is whether regular coffee drinking might protect the brain against cognitive decline in later life.
Long-term studies on the development of dementia:
Interesting data are beginning to emerge from long-term studies on the development of dementia. These truly impressive research undertakings have followed participants for several decades, repeatedly asking them to complete diet and lifestyle questionnaires as well as undergo simple medical testing. Whilst inevitably there is some ‘drop-off’ in the number of participants, the best studies are managing to follow hundreds of patients over many years and are starting to make links between diet and behaviour earlier in life with health outcomes in later years. One example is the ‘CAIDE’ study from Finland which has reported on over 1400 patients citing data collected as far back as 1972 .
A 2010 review of the nine studies that have looked at tea or coffee drinking and dementia in later life found that overall moderate coffee consumption seemed to protect against dementia . The size of the protection differed between studies, with one study reporting a 65% reduction in the risk of dementia. At the other extreme one study found no protection. This kind of difference is not unusual in medical studies, particularly those which rely on self-reporting. The important thing is that the majority of the studies reported an effect in the same direction, and that overall the effect was to protect against dementia. Overall, tea drinking did not seem to have the same effect.
How might coffee influence dementia?
A cup of coffee contains a wide-range of chemicals, and it is unclear which of these is responsible for the protective effect found in these studies. Of course, the most widely recognised compound is caffeine. In low to moderate amounts, coffee acts as a stimulant, increasing alertness and concentration, whilst in higher doses in can cause unwanted effects such as anxiety . It is possible that the repeated low-level stimulation of nerve-cells which results from drinking a cup of coffee stimulates them sufficiently to protect against the decline of dementia. This theory is strengthened if we look at the particular subset of neurons activated by caffeine. If these specific neurons are activated (using medication) in animal experiments, they are protected against cognitive decline . Perhaps the coffee is having just this effect in people. However, tea also contains caffeine (although in much lower amounts than those found in coffee) and so far studies do not see a positive impact of tea-drinking. It may be that the studies are not sensitive enough, or simply that tea does not contain a high enough dose of caffeine to exert an effect.
Coffee also contains high levels of magnesium – this is thought to be protective against type 2 diabetes by increasing the sensitivity of the body to insulin . As we know that diabetes increases the risk of dementia, it may be that coffee acts via this route; reducing the chances of diabetes and therefore protecting against dementia. Coffee also contains antioxidants, and it is possible that these may be protecting the brain. Although different compounds, tea contains higher overall antioxidant levels than coffee though, with a seemingly smaller or absent effect on dementia .
Future steps and development:
Overall, the studies to date show an association between coffee drinking in mid-life and the likelihood of developing dementia in later years. Drinking 3-5 cups of coffee per day reduces the risk of dementia – in some studies by up to 65% . Whilst this may sound like good news for the coffee chains, more needs to be done to investigate how coffee is producing this effect so we can more clearly understand what is going on. For example, what is it in coffee (the caffeine, the magnesium, the stimulating effect on neurons) which is causing the effect; can we reproduce the effect using a single product or compound? In addition, we don’t know whether using either coffee, or the ‘active’ ingredient might protect against progression in patients already showing symptoms of cognitive decline, or if there is something in our coffee cups which might provide a clue as to a new treatment or protection against this ever-rising problem.
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