The report, published in the European Journal of Preventive Cardiology, concludes that, overall, coffee drinking is not a dangerous habit.
In fact, drinking filtered coffee was found to be safer than no coffee at all, but the safest of all, in terms of lowering risk of heart attacks and premature death, was filtered brew.
"Our study provides strong and convincing evidence of a link between coffee brewing methods, heart attacks and longevity," said study author Professor Dag S. Thelle of the University of Gothenburg, in Sweden.
"Unfiltered coffee contains substances which increase blood cholesterol. Using a filter removes these and makes heart attacks and premature death less likely."
Coffee is one of the most popular beverages worldwide and the most frequently used stimulant. Observational epidemiological studies assessing the association between coffee consumption and heart disease mortality display an array of results.
The authors theorised that the heterogeneity in these results indicates that there are population-specific factors, such as brewing method, and that these factors are unevenly distributed across study populations.
They point out in their report that unfiltered coffee contains a substantial amount of the low-density lipoprotein (LDL)-cholesterol, increasing diterpenes kahweol and cafestol that might contribute to a higher risk of heart disease mortality.
Prof Thelle said: "It was unethical to do a trial randomising people to drink coffee or not. So we set up a large population study and several decades later we are reporting the results."
Between 1985 and 2003, the study enrolled a representative sample of the Norwegian population: 508,747 healthy men and women aged 20 to 79. Participants completed a questionnaire on the amount and type of coffee consumed.
Data was also collected on variables that could influence both coffee consumption and heart diseases, so that these could be accounted for in the analysis. For example, smoking, education, physical activity, height, weight, blood pressure, and cholesterol.
Participants were followed for an average of 20 years. A total of 46,341 participants died. Of those, 12,621 deaths were due to cardiovascular disease. Of the cardiovascular deaths, 6,202 were caused by a heart attack.
Overall, coffee drinking was not a dangerous habit. In fact, drinking filtered coffee was safer than no coffee at all. Compared to no coffee, filtered brew was linked with a 15% reduced risk of death from any cause during follow up.
For death from cardiovascular disease, filtered brew was associated with a 12% decreased risk of death in men and a 20% lowered risk of death in women compared to no coffee. The lowest mortality was among consumers of 1 to 4 cups of filtered coffee per day.
Prof Thelle said: "The finding that those drinking the filtered beverage did a little better than those not drinking coffee at all could not be explained by any other variable such as age, gender, or lifestyle habits. So we think this observation is true."
Filtered brew was also less risky than the unfiltered beverage for death from any cause, death due to cardiovascular disease, and deaths from heart attacks. "Our analysis shows that this was partly because of the cholesterol-increasing effect of unfiltered coffee," said the professor.
He noted that unfiltered coffee did not raise the risk of death compared to abstaining from coffee—except in men aged 60 and above, where unfiltered brew was linked with elevated cardiovascular mortality.
"We only had one measurement of coffee consumption, but we know that brewing habits were changing in Norway during the follow-up period. We believe that some women and younger men drinking unfiltered coffee switched to filtered, thereby reducing the strength of the association with cardiovascular mortality, whereas older men were less inclined to change their habits."
Whilst he emphasised that these are observational data, Prof Thelle said that if public health authorities asked for his advice, it would be: "For people who know they have high cholesterol levels and want to do something about it, stay away from unfiltered brew, including coffee made with a cafetière. For everyone else, drink your coffee with a clear conscience and go for filtered."
Source: European Journal of Preventive Cardiology
Tverdal. A., et al"Coffee consumption and mortality from cardiovascular diseases and total mortality: Does the brewing method matter?"DOI: 10.1177/2047487320914443
