The intricate effects of coffee on human health

The details of what we eat is not easy to capture (Photo: Christina Roervik)

The details of what we eat is not easy to capture (Photo: Christina Roervik).

I know, most often on this blog we don’t put much value on epidemiological studies linking disease over decades to food consumption captured by a one-time limited food frequency questionnaire at the beginning of the study period. Knowing the limited reliability of such a food consumption method, intricate relationships between different food groups and changes in food consumption patterns with increasing age it is surprising that it is even called science. But this time it might be different (or is that wishful thinking from our side?).

A new study praises the benefits of coffee

This new epidemiological study of coffee consumption and health is quite elaborate. Firstly, it involved 208,501 participants with 31,956 deaths in three large cohort studies allowing detailed statistical calculations. Secondly, it repeated the food frequency questionnaire each four years to capture food pattern changes. And thirdly, it actually validated the food frequency questionnaire against a multiple week dietary record showing a correlation of 0.74 and reproducibility of 0.80. So a good starting point strengthened by the fact that previous studies have shown that coffee intake is one of the food items showing the highest validity and reproducibility when using food frequency questionnaires and a beverage less prone to misreporting.

Detailed information on caffeinated and non-caffeinated coffee consumption was available as well as other dietary and lifestyle factors. The initial analyses showed a positive correlation between coffee consumption and smoking and because of the deleterious effects of smoking on health, smokers were excluded from the further analyses.

In summary, the good news showed that regular consumption of coffee was inversely associated with risk of total mortality and in particular mortality due to cardiovascular disease and neurological diseases like Parkinson’s. No significant association between coffee consumption and total cancer mortality was found, so unless the International Agency for Cancer Research (IARC) has 799 studies showing the opposite, coffee should be in the clear (I am referring to the dubious nomination by IARC of whole categories of meat or meat products as cancer suspects based on 800 studies we have not yet been able to verify).

Optimal coffee consumption

Three to five daily cups of coffee optimal for health.

Three to five daily cups of coffee optimal for health.

Three to five cups a day seemed to have the optimal protective health effects with the mortality rate 12% less compared to non-coffee drinkers. Similar associations of caffeinated and decaffeinated coffee consumption with risk of total and cause-specific mortality were found. Thus the caffeine is not the protective compound. There are several other compounds in coffee that could be responsible for the positive effects. The authors list chlorogenic acid, quinides, lignans, trigonelline and magnesium as likely contenders as they reduce insulin resistance and systemic inflammation that in turn might prevent diabetes as well as cardiovascular disease.

There could be another reason linked to the dubious findings of IARC and meat consumption. Apart from the obvious culprits associated with meat consumption, like polycyclic aromatic hydrocarbons formed during wood smoking and barbecuing, nitrite added to processed meats and heterocyclic amines formed during high temperature frying, the only compound inherent to meat itself (providing some justification for nominating a whole food category as carcinogenic) is haeme iron. As it happens haeme iron is an excellent source of bioavailable iron, but new research points to excess iron being responsible for a range of human illnesses as well as promoting bacterial growth (in a further blog we will delve into the details of the influence of iron on human health).

Why not try a cup of coffee after dinner?

Now a cup of coffee after dinner inhibits the efficient uptake of iron by the human body. This might be a double whammy in that you can enjoy your red and processed meat without much worry and get an extra kick by the coffee. We told you about the importance of the whole diet with intricate relationships between different food groups.

Maybe IARC should be a bit more careful in the future in looking at individual foods, otherwise it will not be much left to eat. Arsenic in rice cause cancer, too much milk has been associated with prostate and breast cancer, a range of refined and processed foods contribute to weight gain with obesity a factor in cancer development. The list goes on and on. But stick to coffee and you might be fine (although your sleep pattern might be disturbed by a late cup).

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4 thoughts on “The intricate effects of coffee on human health

  1. It is not clear why you bring in the IARC conclusions on processed and red meat, but suffice to mention that one of the many studies reviewed by the IARC experts was a key epidemiology study conducted by the Harvard School of Public Health that also conducted this coffee study which you admire.

    • I love to see some reaction to my blog and this was a bit of a teaser. Many thanks Gerry, it gets more lively this way. As mentioned I will come back to the iron issue and when more detail is available I will comment further on the IARC conclusions. Just as an aside, in the Harvard study on coffee I based the blog on they mentioned an association between frequent coffee consumption and higher alcohol and red meat consumption. Still they found no association between coffee consumption and colorectal cancer. That’s the reason I brought in the IARC conclusions, although not mentioned specifically. This is a bit of an anomaly since I assume that the study you mentioned that IARC included from the same team in their evaluation must have used the same cohort groups. Obviously you can cut the material in different ways and get different results. Quite confusing don’t you think?

  2. You are right, Stefan, that the IARC report has created risk communication fiasco. Part of the reason for this, I believe, is that the report was really targeting policy-makers and not consumers themselves since dietary habits of adults are nearly impossible to change, especially with something as ‘beloved’ as meat and meat products. So the net impact might be that nutritional guidelines in the future would be amended to suggest that these products are qualified as ‘healthy’, but with limitations. This is in contrast to the recommendations for fruits and vegetables, i.e. ‘eat as much as you want’. However, for the most part, consumers have ignored this advice.

    A more serious impact of the report will be on the developing countries where the adoption of the Western diet has been associated with increases in cardiovascular disease, diabetes and cancer. I have to add the meat production can contribute to food insecurity because it is very inefficient compared to plant protein and to environmental degradation (water in particular) and greenhouse gas emissions. Until we can find an acceptable alternative (like electric automobiles), the idea that billions of people might start to consume the Western diet is clearly unhealthy and unsustainable.

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