November 22, 2017

expert reaction to paper looking at drinking coffee and health

Scientists evaluate the existing evidence for associations between coffee consumption and multiple health outcomes, in the BMJ.

Ms Catherine Collins, Registered Dietitian, said:

“This review builds on previous reviews to summarise the role of coffee in health.  Despite the limitations of assessing habitual coffee in population studies, what is reinforced in this review is that not only are 2-3 cups of coffee a day associated with health benefits, taking a couple more daily didn’t appear to be detrimental, either.  There are confounding factors in coffee drinkers that may explain some of the effect, but the large numbers of studies used with consistency of reported effects make it more likely that coffee is responsible for the effects seen.

“Perhaps the most interesting aspect of this extensive review is the potential beneficial role of coffee in heart health.  Advising people with heart problems to avoid coffee is a common but outdated theme of cardiac diet advice, loosely based on the cardiac effects of caffeine.  This review neatly summarises that around three cups of coffee a day is reported to be the magic number associated with reduced population risk of death, around 19% lower for cardiovascular disease in coffee drinkers compared to non-drinkers, and around 30% lower for stroke.  Risk of death following a previous heart attack was 45% lower in ‘high’ coffee drinkers compared to those drinking little coffee each day.  The data here are relevant to populations rather than individuals so we can’t give recommendations (and there is also individual variation in response to caffeine), but the size and consistency of effects and level of evidence seen is convincing.  These kinds of effects if seen in trials of heart medicines for example would be convincing evidence of a benefit of that medicine.

“Moderate coffee intake was also associated with reduced risk of type 2 diabetes and metabolic syndrome, both conditions also being associated with an increased risk of heart disease.  The reason for this is unknown, but it could be related to the effect of coffee on improving liver function.  Equally, it could well be that a virtually calorie-free cup of black coffee with a dash of milk is a low calorie and low sugar alternative to a fruit juice or sugary drink, so helping reduce sugar intake.

“The limits of this review stops with the finding that 2-3 cups of coffee a day are likely to be largely beneficial to health.  It’s impossible to break down the data further to try to find out why coffee should be so useful to health.

“We know that coffee beans contain hundreds of biologically active compounds.  Caffeine, anti-oxidant chlorogenic acids and the diterpenes cafestol and kahweol are key bioactives found in coffee proved beneficial to human health.  The authors suggest that the benefits of coffee, dose related up to 3-4 cups a day, is related to increasing diterpene intake.  But the diterpene content of coffee varies tremendously.  Brewed Scandinavian, Turkish style or French press coffees are all diterpene-rich.  But instant and filter coffees are diterpene-free.  If diterpenes are the reason for coffee’s health benefits, instant coffee and drip-brew filtered coffee would be pretty useless given their negligable diterpene content.  However, given that diterpenes are considered the bioactives marginally raising both total and LDL (‘bad’) cholesterol levels (but not to a level of concern from the data presented in this study), there may well be a health benefit from combining different types of coffee throughout the day to balance out diterpene intake.  The caffeine content of coffee is also highly variable, depending on both bean and blend.  Roasting influences caffeine content, with light roasted beans being higher in caffeine than dark roasted ones.

“Hydration is a major contributor to good health and drinking regularly throughout the day is essential.  Whilst a mug of coffee provides 300ml towards daily fluid goals, a single espresso provides less than 40ml.

“Adding milk, cream or a coffee-shop muffin to accompany your coffee also impacts on overall diet quality and effect on health.  Whilst the authors could cleanse ‘coffee and cig’ data from their analysis, the potential impact of coffee shop culture on both coffee and calorie intake that’s emerged since much of this data was generated is beyond the scope of this review – the authors controlled for smoking but they didn’t or couldn’t control for diet.

“Does international and personal preferences for different coffee types weaken the findings?  Unlikely.  Firstly, this objective summary is a collection of already published research in the field of coffee research that shows common themes of health benefit.  Nutrition research has long since recognised that attempting to define and isolate a particular substance within a foodstuff (the ‘reductionist approach’) to identify the key substance influencing a health function is impossible.  It’s often stated the that smallest unit of research we should be investigating is a food, not its content.

“On this basis, with the exception of pregnant women in the first three months of pregnancy, we can continue to enjoy a few cups of coffee daily.”

Prof. Tom Sanders, Professor emeritus of Nutrition and Dietetics, King’s College London, said:

“While the conclusion is reassuring to coffee consumers, there are some limitations.  Coffee is known to cause headaches in some people and it also increases the urge to go to the toilet – some people chose not to drink coffee for these reasons.  Patients with abnormal heart rhythms are often advised to drink de-caffeinated coffee.  Caffeine also acutely increases blood pressure, albeit transiently.  Consequently, there is likely to a bias towards better health in those who chose to drink coffee compared to those that avoid it, who may do so because they have health problems – this is a limitation of the studies this review looked at as these factors weren’t always taken into account.

“While the review and accompanying editorial warns about adding sugar to coffee it does not stress the importance of how the coffee is prepared.  There is strong evidence from other research to show that boiled coffee or cafetiere coffee can increase blood cholesterol levels – this effect was seen most strongly in Norway and Finland.  The review, however, does show that filtered coffee does not have any significant effect on blood cholesterol levels whereas unfiltered coffee was associated with a raised LDL cholesterol (by about 0.3 mmol/L, which is about the same effect size as replacing 5% of energy from unsaturated fats with saturated fatty acids).  This size increase in LDL cholesterol would be expected to increase risk of CHD by about 6%.  Recent dietary guidelines in the Netherlands advise drinking filtered or instant coffee that have much lower levels of the terpinoids compounds (kahweol and cafestol) that are responsible for the blood cholesterol raising effects.”

Dr Chris Alford, Associate Professor in Applied Psychology, University of the West of England, said:

“This is good quality research – it is a review of previous meta analyses of work in this area.  The authors have indicated that confounders are a problem and are not always controlled for, or not controlled for in a similar way, such as smoking.

“The review includes both the observed benefits and harms of coffee consumption.  The stated harms include adverse effects on pregnancy and is appropriately covered in the full review.  However, the summary statements might usefully have indicated that the potential adverse effects observed in pregnancy were for higher compared to lower coffee consumption.  There were none seen for all coffee consumption compared to no coffee – and so mothers to be need not panic but might want to limit their coffee consumption to 2 cups per day in line with the recent European guidelines on caffeine (EFSA 2015).

“The authors and editorial are at pains to point out that the presented health benefits of coffee consumption are based on associations and are not shown to be causal.  Better controlled and prospective studies are needed in order to establish causal relationships.  Associations can be due to higher order factors (other factors not directly investigated in the research but which are responsible for causing the observed common effects or associations), as pointed out by the authors.  They are right to indicate that we should not decide to consume coffee based on health benefits or to prevent disease.”

Dr Amelia Lake, Reader in Public Health Nutrition, Teesside University, said:

“This paper is a review of previous evidence and the authors state the evidence they reviewed wasn’t of very high quality.  The press release reflects the science well.

“Is coffee good for you?  That may be a simple question, but as with most things dietary related, there isn’t a simple answer!  This paper should not be interpreted as meaning we should all drink coffee for good health, because it is not possible to directly make the link with this kind of study, and because there are too many lifestyle and other confounding factors.  Coffee drinking is tied up with other factors and behaviours related to health and our socio-economic circumstances and it is difficult to unpick all the factors.

“I don’t think that there is going to be a shift in the dietary advice we would give populations or individuals based on this review – coffee can be part of a healthy balanced diet.  Coffee drinking is safe in moderation and the lowest disease risk in this review was found at 3-5 cups per day – but this doesn’t apply to pregnant women or women at risk of fractures.  Something to bear in mind is that your coffee often comes with high fat, high sugar products such as flavoured syrups and we are clear that these are not good for health!”

Dr Oyinlola Oyebode, Associate Professor, Population Evidence and Technologies at the Warwick Medical School, University of Warwick, said:

“This press release accurately reflects the science, the main conclusions being that moderate coffee consumption is not just safe, but more likely to be associated with benefits to health rather than harms to health in the majority of the adult population (pregnant women, and women at risk of fractures being the exceptions).  This is high quality research – systematically taking into account a large amount of primary data.  There is other recent data, not included in this study which supports the study findings (an observational study of more than half a million people across 10 European countries which found that those drinking more coffee had lower mortality¹).

“Because the majority of the primary data included in the BMJ paper, and the large European study described above, is observational rather than experimental data, there is the possibility that the association of coffee consumption with better health is due to something else that coffee drinkers are more likely to do.  The implication of the research is that the benefits of coffee should be explored in a randomised trial – to see whether it is worth recommending for health reasons.”

1 Gunter MJ, Murphy N, Cross AJ, Dossus L, Dartois L, Fagherazzi G, et al. ‘Coffee Drinking and Mortality in 10 European Countries: A Multinational Cohort Study’. Annals of Internal Medicine. 2017 Aug; 167(4):236-247

* ‘Coffee consumption and health: umbrella review of meta-analyses of multiple health outcomes’ by Robin Poole et al. published in the BMJ on Wednesday 22 November 2017. 

Declared interests

Dr Amelia Lake: “Amelia works for Teesside University and is an Associate Director of Fuse a UK CRC Centre for Excellence.  Amelia is a registered dietitian, a registered nutritionist (Public Health), a member of the Association for the Study of Obesity, The Nutrition Society and a member of the British Nutrition Foundation’s Scientific Advisory Committee.”

Dr Oyinlola Oyebode: “I don’t have any interests to declare.”