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Higher coffee intake related to lower IHD mortality over last 20 years

A greater coffee intake has been found to be inversely associated with levels of ischaemic heart disease and mortality in 147 countries over the last 20 years according the findings of an ecological study by Japanese researchers.

Coffee is a complex mixture of more than a thousand different chemicals, many of which are reported to be biologically active and its health-promoting properties are attributed to this rich phytochemistry. In fact a 2017 review found health benefits from coffee intake including a reduced all-cause mortality, cardiovascular mortality as well as cardiovascular disease and a lower risk of several specific cancers, neurological, metabolic, and liver conditions.

Nevertheless, previous studies on the association between coffee drinking and cardiovascular disease do not suggest a beneficial health effect and actually imply that coffee drinking is potentially harmful.

For instance, in a 1963 study, it was reported that the development of clinical coronary heart disease¬†was associated with coffee intake. Furthermore, another study from the 1970’s concluded that there was a small risk of death from coronary heart disease linked to drinking coffee.

Finally, a study from the 1980’s supported an independent, dose-responsive association of coffee consumption with clinically evident coronary heart disease, consistent with up to a threefold elevation in risk among heavy coffee drinkers.

Nevertheless, over the subsequent decades, the link between coffee drinking and cardiovascular disease has moved from no noticeable effect to a protective effect such that there was a significant and inverse relationship with cardiovascular disease.

But why has the relationship between coffee intake and ischaemic heart disease (IHD) incidence and mortality changed over the years? This was the question asked by the Japanese team who undertook a longitudinal, ecological study between 1990 and 2018.

The team were able to use the Global Burden of Disease (GBD) Study to extract age-standardised IHD incidence and mortality and the Global Dietary Database to determine population level coffee intake data for a large number of different countries included in the Global burden of disease study from 1990 to 2018.

Coffee intake and ischaemic heart disease

Overall, the Japanese team used data from 147 countries, each with over a million inhabitants. Coffee intake, based on cups/day/population increased from a mean of 0.4 in 1990 to 0.8 in 2018 (p < 0.001). However, more interesting was that IHD incidence reduced over the same period of time from 338.7 cases/100,000 population in 1990 to 311.2 in 2018 (p = 0.073). In addition, a similar, but this time, statistically significant reduction occurred with IHD mortality (187.6/100,000 to 147.5, p < 0.001).

Using regression models adjusted for several lifestyle factors including smoking levels, physical activity and alcohol intake, it became clear that there was a significant inverse association between coffee intake and year as well as IHD incidence and mortality. In other words, the positive or harmful association between coffee intake and IHD mortality seen in the 1990’s changed to one of an inverse association and therefore protective effect over time.

In trying to understand why these changes had occurred, the authors speculated that the harmful effects of coffee in relation to IHD were probably related to confounders such as smoking, i.e., many people enjoy smoking a cigarette with their coffee and as smoking increased the risk of IHD, which may account for the observed positive association.

Some support for this comes from a study which observed that smoking is known to modify the observed risk when studying the role of coffee on human health.

Another possible reason for the change in observed health effects of coffee might be due to a shift from drinking boiled to filtered coffee. It was known that some ingredients in boiled coffee raised cholesterol levels and later work showed that the hyper-cholesterolaemic agent present in boiled coffee is retained by the paper filter.

They concluded that their study suggested how the association between coffee intake and IHD risk may change over time owing to changes in social and environmental factors.

Shirai Y et al. Change in the association between coffee intake and ischemic heart disease in an international ecological study from 1990 to 2018 Sci Rep 2022