If there wasn’t already enough good reasons to justify the average Australian adults’ love of coffee, scientists have just uncovered another one. An Australian-based study of healthy human volunteers has found that the active components of coffee (i.e. polyphenols) can confer improved blood sugar and insulin control when consumed with a meal. While previous epidemiological and animal studies have hinted at such actions of coffe, this is the first proper study in humans to uncover such findings.
Another marker that responded positively to the 350mg of coffee polyphenols administered with the test meal was vascular endothelial function or more simply put - blood flow. All nitric oxide supplements aim to increase blood flow and associated vascular endothelial function, so it’s exciting to think that something as simple as a cup of coffee can do the same. Importantly, however, this effect is not thought to be due to coffee’s caffeine content.
Compared with when they consumed the placebo drink, subjects were found to exhibit significantly lower blood glucose levels and greater blood vessel dilation1. This coincided with a significant increase in the level of a gut-derived hormone called glucagon-like peptide 1 (GLP-1)1.
GLP-1 is called an incretin hormone that is released from the gut and helps stimulate insulin release from pancreatic beta-cells. It happens to be the same hormone that is secreted with ingestion of whey protein (in particular whey protein hydrolysate). This is thought to be the mechanism underlying the documented benefits of regular whey protein consumption on blood glucose and diabetes control2.
The extent to which blood sugar stays elevated following a given meal is one of the key risk factors for diabetes and cardiovascular disease. So in this sense, anything that lowers post-meal blood glucose levels is great news for the management of chronic disease. Lower blood glucose levels essentially lowers oxidative stress as well, given that glucose is a highly reactive substance, such that sustained levels lead to a higher oxidative stress burden.
Before everyone gets too excited and starts claiming that any and every type of coffee has the potential to lower blood sugar and improve blood flow, it’s important to highlight exactly what type of coffee subjects in the study consumed. First and foremost, the coffee was standardised for its polyphenol content, which amounted to 350mg per serve. Of this, 72.4% was chlorogenic acid (the most well known coffee antioxidant), 19.3% was feruloylquinic acid and 8.3% was dicaffeoylquinic acid. The coffee beans used to prepare the extract were Robusta species.
Coffee happens to be the richest food source of chlorogenic acid, but its content can vary widely between coffee species. As a rule, the extent of roasting that a bean has undergone is a key factor in determining chlorogenic acid levels, with light roasts possessing higher levels and vice versa3.
It’s important to note that both the placebo beverage and coffee beverage contained 54.9mg of caffeine each. As such, the researchers suggested that the caffeine content per se of coffee has little to do with its beneficial effects of blood glucose control.
- Jokura H, et al. Coffee polyphenol consumption improves postprandial hyperglycemia associated with impaired vascular endothelial function in healthy male adults. Nutrition Research. 2015. [in press]
- Jakubowicz D, et al. Incretin, insulinotropic and glucose-lowering effects of whey protein pre-load in type 2 diabetes: a randomised clinical trial. Diabetologia. 2014 Sep;57(9):1807-11.
- Moon J-K, et al. Role of roasting conditions in the profile of volatile flavour chemicals formed from coffee beans. Journal of Agriculture and Food Chemistry. 2009; 57:5823–5831.