Dr Kevin McCarroll
Medical Matters
Coffee is one of the most widely drank beverages in the world and indeed in Ireland is consumed by about 75% of the population.
While many of us are familiar with the caffeine boost we get from coffee, it is actually only one of up to 1000 bioactive compounds it contains that may have therapeutic or negative effects on our health.
Given the rise in coffee consumption, it invites the question as to whether coffee is good or bad for us or is the adage of “everything in moderation” applicable.
To help answer this question, there has been a number of recent large studies exploring coffee intake and health outcomes, the most comprehensive of which was published this month in the British Medical Journal and garnered much attention.
The scope of research was broad, reviewing over 201 studies (which of themselves pooled results from several other studies) and looked observationally at coffee consumption and 67 health outcomes.
The results are reassurring for those of us who are coffee drinkers. In a nutshell, findings suggest that coffee (within usual levels of intake) is usually safe and more likely to be of benefit than harm.
Benefit
However, the relationship was non-linear with some outcomes indicating the greatest potential benefit in those who drank between three and four cups per day.
In particular, this level of consumption was associated with a 17% lower risk of all cause mortality, 15% reduction in cardiovasclar disease, 16% lower risk of dying from coronary heart disease and a 30% reduction in stroke mortality.
While increasing intake beyond this was not associated with harm, the benefical effects were smaller.
Furthermore, in a sub-analysis of 40 studies where subjects where followed up, any coffee consumption versus none was associated with a 13% reduction in the incidence of cancer rising to a 18% decrease when comparing high versus low intake.
Notably, in this latter group reduction was seen for cancers of the prostate, oral cavity, womb and liver as well as melanoma, other skin cancers and leukemia. However, no effect was evident for some common cancers including that of the bowel, breast and ovaries.
Interestingly, coffee intake was also associated with a lower incidence of Parkinson’s, Alzheimer’s, certain liver diseases, depression and diabetes. Many of the associations also held true for decaffeinated coffee implicating a potential effect mediated by other coffee consituents.
Finally, some controlled intervention trials of coffee found no overall effect on blood pressure or cholesterol.
So what do these results actually mean and should we alter our coffee consumption?
Firstly, there are number of caveats with this type of research with studies simply looking at associations with coffee intake and outcomes albeit after variable periods of time.
There may be differences in socioeconomic, lifestyle and dietary factors in coffee drinkers that are not all accounted for in studies and could help explain any links.
The reliability of self-reporting of coffee intake, the potential lack of constancy of consumption over time and differences in what constitutes a cup could lead to inaccurate estimates of overall coffee exposure.
Studies did not indicate what type of coffee was consumed with methods of roasting, bean type and preparation method known to affect the content of bioactive compounds that could have positive effects. In addition, gut microbiome can affect absorption of coffee derivatives and genetics may also affect their metabolism. For example, in the case of caffeine, some individuals metabolise it at a greater rate altering the effect of a given amount of coffee.
Beyond caffeine, the biological plausibity for any positive effect of coffee relates to the presence of compounds such as chlorogenic acid and polyphenols which have significant antioxidant and anti-inflammatory properties.
Indeed, coffee has been shown to contribute to a greater proportion of daily intake of dietary antioxidants than tea, green fruit and vegetables in some studies. Other compounds including cafestol may induce the breakdown of carcinogens. Caffeine also appears to increase dopamine release in the brain, the main neurotransmitter which is deficient in Parkinson’s and, as well as others, important in Alzheimer’s.
However, the recent study results for coffee were not all good. Higher versus low coffee consumption in pregnancy was associated with a higher risk of low birth weight (31%), pregnancy loss (46%) and preterm loss (up to 22%).
One factor may be caffeine which crosses the placenta and is not metabolised as quicky in the foetus. Indeed, it is recommended that pregnant women should limit caffeine intake to 200 mg daily. Coffee was also associated with an increased risk of fracture (14%) though only in women.
In conclusion, given the consistency of findings for most outcomes across numerous large studies, it appears that coffee is generally safe and may possibly be beneficial apart from in pregnancy and in those with brittle bones at risk of fracture.
However, people who are sensitive to the effects of caffeine should consider avoiding it or taking decaffeinated varieties which may still confer a benefit. Remember too, that coffee can aggravate migraine, acid reflux and other conditions!
Dr Kevin McCarroll is a Consultant Physician in Geriatric Medicine, St James’s Hospital, Dublin.