Writing in the European Journal of Nutrition, researchers noted that previous studies have shown conflicting results regarding whether drinking coffee has a beneficial or harmful effect on endothelial function (EF) and cardiovascular (CVD) risk. A healthy endothelium is recognised to be associated with lower blood pressure and risk of CV events. Endothelial dysfunction (ED) involves the presence of an excess of substances that make the arteries constrict (vasoconstriction). ED is widely recognised to be a cause of high blood pressure and a predictor of CVD and CV events.
The difference in findings may be the result of varying levels of chlorogenic acids (CGAs) (polyphenols) and hydroxyhydroquinone (HHQ) content of the coffee, suggest the research team from Hiroshima University, Japan.
In this study, coffee with high CGAs but low HHQ content significantly improved post-prandial EF. Conversely, neither high-CGA-high-HHQ coffee, nor placebo had any effect on EF.
“A single intake of coffee with a high content of CGAs and low HHQ is effective for improving postprandial endothelial dysfunction,” noted lead researcher Professor Yukihito Higashi.
The scientists also found that changes in blood CGAs level two hours after drinking coffee correlated with the extent of FMD improvement.
The study was a single-blinded randomised placebo-controlled crossover trial incorporating 37 people with borderline or early stage hypertension.
Participants consumed a single intake of 185g of either Beverage A (high-CGA, low HHQ), Beverage B (high-CGA, high- HHQ) or Beverage C (placebo- zero CGA, low HHQ). All beverages contain similar amounts of caffeine.
Study 1 group were randomised to either A or B, while the Study 2 group consumed either B or C. The crossover was separated by a 7-day washout period. The subjects also fasted for 12 hours before the coffee intake.
The researchers measured EF two hours after coffee consumption and compared the change versus baseline. They assessed EF in terms of flow-mediated vasodilation (FMV), (a measure of relaxation of the arteries) and blood 8-isoprostane content (a marker of oxidative stress).
CGA and HHQ in coffee
Coffee is a complex chemical mixture of many compounds, including CGAs, HHQ and caffeine. Previous research has shown that CGA has a blood pressure lowering effect and can improve EF. However, in an animal model of hypertensive rats, HHQ blocked the EF-restorative benefits of HHQ; while in another study, HHQ induced higher levels of oxygen free radicals.
There is a wide public perception that coffee raises blood pressure due to its caffeine content. However, “Some clinical studies have shown that coffee with a high content of CGAs and a low content of HHQ is effective for reducing blood pressure with mild hypertension,” revealed the researchers.
Therefore, the balance of beneficial versus harmful effects on EF (and possibly on blood pressure) might depend, among other factors, on how it is prepared.
“Roasting coffee results in the loss of CGAs and generation of HHQ,“ explained the researchers.
“Intake of coffee with reduced HHQ per se also may be beneficial for maintenance of vascular function and prevention of CV events,” they added.
Although no reductions in blood pressure were seen in this trial, the researchers suggested that longer-term interventions were needed to identify sustained effects over time.
“Further studies are needed to assess the long-term effects of drinking coffee with a high content of CGAs and low content of HHQ on vascular function, onset of CVD, and CV events,” concluded Higashi.
Source: European Journal of Nutrition
Published online, doi: 10.1007/s00394-018-1611-7
“Coffee with a high content of chlorogenic acids and low content of hydroxyhydroquinone improves postprandial endothelial dysfunction in patients with borderline and stage 1 hypertension”
Authors: Masato Kajikawa, Yukihito Higashi et al