Drinking coffee daily is associated with increased risk of cardiovascular events - mainly heart attacks - in young adults with mild hypertension, a new 12-year study has warned.
The study in more than 1,200 patients found that heavy coffee drinkers had a four-fold increased risk of cardiovascular events while moderate drinkers tripled their risk.
Future prediabetes attenuated the associations suggesting that the effect of coffee on cardiovascular events may be mediated by its long term influence on blood pressure and glucose metabolism.
"There is controversy surrounding the long term cardiovascular and metabolic effects of coffee consumption in patients with hypertension," said Dr Lucio Mos, a cardiologist at Hospital of San Daniele del Friuli in Udine, Italy.
"Our study was designed to evaluate whether coffee drinking had an effect on the risk of cardiovascular events, and if the association was mediated by effects on blood pressure and glucose metabolism," Mos said.
The study included 1,201 non-diabetic patients aged 18 to 45 years who had untreated stage 1 hypertension.
Coffee consumption was categorised by the number of caffeine-containing cups per day: non-drinkers (zero), moderate (1-3) and heavy drinkers (4 or more).
Among the participants, 26.3 per cent were abstainers, 62.7 per cent were moderate and 10 per cent were heavy coffee drinkers. Coffee drinkers were older and had a higher body mass index than abstainers.
There was a linear relationship between coffee use and risk of hypertension needing treatment. The association reached statistical significance for heavy drinkers.
As type 2 diabetes often develops in hypertensive patients at a later stage, the study examined the long term effect of coffee drinking on the risk of developing prediabetes.
A linear relationship was found, with an increased risk of prediabetes in heavy coffee drinkers.
However, the risk of prediabetes related to coffee consumption differed according to the CYP1A2 genotype, which determines whether individuals are fast or slow caffeine metabolisers.
The risk of prediabetes was increased significantly only in slow caffeine metabolisers.
"Drinking coffee increases the risk of prediabetes in young adults with hypertension who are slow caffeine metabolisers," said Mos.
"Slow caffeine metabolisers have longer exposure to the detrimental effects of caffeine on glucose metabolism. The risk is even greater if they are overweight or obese, and if they are heavy coffee drinkers.
"Thus, the effect of coffee on prediabetes depends on the amount of daily coffee intake and genetic background," Mos said.
The study was presented at the ESC Congress 2015 in London.
