From a Cappuccino to a Latte, coffee is the most popular drink world-wide – with over 400 billion cups consumed each year. Coffee has a stimulating effect because of its caffeine content, making it no surprise that it’s commonly used as a quick ‘pick me up’ to promote wakefulness and to improve mood and cognition.

In fact, coffee also contains many other substances which could prove beneficial for our health including; antioxidants, chlorogenic acid, quinides and magnesium. Initially, coffee was related to negative lifestyle factors such as cigarette smoking and inactivity, but it seems more recently that coffee may actually have a number of positive health benefits (Muriel & Arauz, 2010). Over the years considerable research has looked to discover the health effects of this popular drink, and it seems that the one thing we can be sure of coffee causing is much debate.

The Good

Source of antioxidants

Coffee is a good source of antioxidants, which help to prevent cell damage and strengthen the immune system to fight infection and disease. In fact, research has found coffee to provide more antioxidants than both fruit and vegetables combined (Svilaas, 2004).

Diabetes

Research has reported that higher coffee consumption may lower the risk of type 2 diabetes. This was found in studies investigating the effects of both caffeinated and decaffeinated coffee, suggesting that something other than coffee’s caffeine content may be causing this effect.

In addition, the antioxidants in coffee may help to prevent insulin resistance and impaired glucose tolerance (Herbst, 2011). One study found that the consumption of 12 cups a day significantly reduced the incidence of diabetes by 67%, giving positive implications on high coffee consumption in reducing type 2 diabetes. However, it is uncertain whether the results from this study were caused by coffee intake or as a result of other unmeasured factors (Zhang et al., 2010).

Although the majority of research has found that coffee consumption may help to reduce the risk of type 2 diabetes, some studies have not found this association and the mechanism behind this possible effect still remains unclear.

Dementia

Accumulating evidence has associated coffee drinking with a reduction in cognitive decline, subsequently protecting against neurodegenerative disorders such as dementia (Arab et al., 2013). It has been proposed that moderate consumption of coffee may lower the risk of dementia and Alzheimer’s disease. In one study, drinking 3-5 cups a day at midlife was linked with a reduced risk of dementia by 65% later on in life. The mechanism behind this is still unclear but could be down to the antioxidants found in coffee (Eskelinen & Kivipelto, 2010).

Prostate Cancer

A strong inverse association has been found between regular coffee consumption and the risk of prostate cancer (Wilson et al., 2011). Similarly, further research found higher coffee consumption to reduce the risk of aggressive prostate cancer but on the other hand was not found to reduce the overall risk (Shafique, 2012). More recently, this inverse association was again identified and suggested that the antioxidants in coffee may be responsible for this effect, as dietary antioxidants have previously been related to a decreased risk of advanced prostate cancer. However, more research is required to determine this (Discacciati et al., 2013).

Asthma

As previously mentioned, coffee has a high caffeine content and caffeine has been reported to lower respiratory muscle fatigue and act as a weak bronchodilator (widening the airways). Research investigated the effects of caffeine on asthma and found that caffeine modestly improved airway function for up to four hours in asthmatics. Though this research has positive implications, it is unknown whether taking caffeine actually leads to symptom improvement and if so, how much caffeine needs ingesting to see these improvements? It may be that large amounts are required and that the effects of high amounts of caffeine may actually cause other complications. Nevertheless, more research is needed in this area (Welsh et al., 2010).

Parkinson’s Disease

Research has found that higher coffee and caffeine intake could significantly lower the occurrence of Parkinson’s disease (Ross et al., 2000). Likewise, a recent meta-analysis suggested that caffeine consumption may provide a 25% reduction in the risk of developing Parkinson’s disease. It seems plausible that the mechanism of this effect is probably related to the caffeine content in coffee, as caffeine may have a neuroprotective effect by activating specific signalling pathways in the brain. Nevertheless, as we know, coffee contains many other compounds which could also play a role in the possible prevention of Parkinson’s disease (Costa et al., 2010).

Liver Disease

Initially, research identified a positive link between the effects of coffee on alcoholic liver disease. After further research, the positive effects of coffee on liver function and liver disease, including hepatocellular carcinoma, cirrhosis and liver enzymes were also found (Molloy et al., 2012). More recently, caffeine was suggested to lower the risk of non-alcoholic fatty liver disease (NAFLD), implying that coffee may have a potential protective effect (Birerdinc et al., 2012).

Depression

Caffeine has a positive effect on neurotransmitters in the brain such as serotonin, dopamine and noradrenaline, which are involved in depression. This suggests that caffeine may contribute to an antidepressant effect. A longitudinal study found the risk of depression to decrease with an increase in caffeinated coffee consumption. Suggesting a possible protective effect of depression from coffee consumption.

Furthermore, a large US study found a relationship between higher coffee consumption and lower risk of suicide. However, studies in this area have been observational and do not prove that coffee intake directly causes a reduction in suicide risk as many other factors may also play a part. As with many other effects of coffee, the mechanism is unclear and research needs to assess the impact that decaffeinated coffee has on depression (Lucas et al., 2013).

The Bad

Blood Pressure

A link between coffee and blood pressure was first reported 75 years ago, but research is now trying to establish whether coffee consumption is linked to hypertension risk (Zhang et al., 2011). Coffee contains a high caffeine content which in turn can elevate blood pressure (Higdon & Frei, 2006). One review concluded that coffee consumption is related to a higher blood pressure (Jee et al., 1999). Research investigating the effect of coffee consumption on hypertension risk still seems unclear, although most evidence suggests regular coffee intake does not increase this risk (Gelenijnse, 2008).

Osteoporosis

Research has looked into the effect of coffee consumption and calcium balance, generally suggesting that caffeine intake from coffee consumption may reduce the absorption of calcium. This suggests that coffee intake could lead to osteoporosis, which could be problematic especially in those who already lack sufficient calcium (Hallstrom, 2013). Initial research proposed that very high coffee consumption could lead to extra calcium loss, whilst consumption of 1-2 cups would have little impact on calcium balance (Hasling et al., 1992). However, subsequent studies have been contradictory.

Teeth

One thing we can be sure of is that coffee consumption can stain the teeth. Research found that daily coffee consumption leads to an increase in yellowness and a decrease in brightness of the teeth (Joiner, 2004).

Coronary Heart Disease (CHD) and Mortality

It is well known that caffeine intake can increase blood pressure and heart rate and can even cause palpitations. Earlier studies have linked heavy coffee consumption to an increased risk of CHD. One study in particular found that this risk was not dependent on the brewing method used or the current risk factors for CHD (Happonen et al., 2004). However, more recent studies have suggested that moderate coffee consumption may actually reduce the risk of CHD mortality (de Koning Gans et al., 2010; Sugiyama et al., 2010).

In contrast, recent research has evaluated the association between coffee consumption and mortality from all causes and from cardiovascular disease. Researchers found a positive association between consumption and mortality in those younger than 55, implying that younger people should potentially avoid drinking more than 4 cups of coffee per day. However, the long term effects on all cause and cardiovascular disease mortality still needs assessing. But don’t spit out your coffee just yet, this correlational study won’t have accounted for many other factors which may relate to mortality (Liu et al., 2013) and many studies have found conflicting results (Freedman et al., 2012). Therefore the effects of coffee on CHD and all-cause mortality still remain controversial.

Summary

In summary, it appears that research has identified both good and bad effects of drinking coffee. However, it is important to be aware that a lot of studies have been based on observational data which cannot prove causation and so it is hard to draw any definitive conclusions. However, at this stage it does seem as though the good may outweigh the bad, so why not have that coffee after all?

Adie Blanchard – Researcher

References

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