Confused about coffee and diabetes? Not sure if your morning coffee is giving you diabetes or preventing it? I’m not surprised. Historically coffee has been deplored as an unhealthy vice. But recently there’ve been some big claims the other side of the spectrum… So should you believe the hype? Can coffee actually play a role in preventing diabetes?
In the last ten or so years, there have been many studies (like this and this) looking into the relationship between coffee and diabetes. Most have found the same link: coffee drinking is associated with lower incidence of diabetes!
A recent review, which was conducted in 2013, looked at 28 studies, with over one million people – and found strong support for this link. The evidence appears to be consistent across various ethnicities and showed a dose-response relationship, that is, the more coffee people drank, the lower their relative risk of developing diabetes. One study even showed those who decreased their coffee consumption increased their risk of diabetes, while those who increased consumption, decreased their risk!
Even though this is a lot of people and many studies, it’s important to note, these were epidemiological studies. So it’s just observational evidence. Epidemi.. What? Epidemiological evidence means that people have conducted studies of large populations of people and found a pattern – or association – between people and a disease. The pattern seen in diabetes is that those who drink coffee seem to have less diabetes.
“One Triple Shot Latte to go”?
Before you go out and over-caffeinate yourself, let’s break this down. Firstly, what these studies show is just an association, not a cause. That is, not drinking coffee will not cause you to get diabetes, and drinking coffee will not prevent diabetes. It just means there’s a pattern between coffee drinkers that shows they seem to get diabetes less often. There could be a lot of other reasons for this link, for example, do coffee drinkers also exercise more? Many of these studies have done detailed analyses to try to rule out other causes (also called confounders). But it’s still impossible to show cause in these type of population studies. We need experimental studies (particularly randomised control trials) for this.
One randomised, crossover, controlled study looked at the short-term effects caffeinated coffee on glucose metabolism in healthy men. It found that realistic doses of coffee had no significant effect on blood glucose levels.
Unfortunately, there is a lack of experimental studies showing the long-term effect of drinking coffee and diabetes prevention. It seems those studies that have been carried out didn’t go for long enough or have enough participants to show cause. Of course, for practical reasons, it is difficult to do long experimental studies of this type. Just think about it: would you give up coffee (or starting drinking it) for years just for the sake of an experiment?!
As well as trials, before we (as health professionals), start sending everyone out for coffee, we need to understand how coffee might help to prevent diabetes.
So How Does it Work?
Good question. We don’t actually know.
In fact, there is a lot of evidence showing that short-term coffee (specifically caffeine) consumption increases insulin resistance and blood sugar levels. Yes, the opposite of preventing diabetes!
Could coffee drinking still play a role in reducing the risk of type 2 diabetes in the long-term despite this? Well, it’s possible that habitual coffee drinkers may adjust to the negative effects of caffeine on insulin and blood glucose over time. Or perhaps the other compounds in coffee are just so good at lowering blood sugar they cancel out the negative effects of the caffeine!
The Sciencey Stuff: Coffee and Diabetes
Several plausible mechanisms have been suggested in the association between coffee and diabetes risk reduction. Trials have shown that consuming coffee polyphenols improves postprandial hyperglycemia (i.e. the rise in blood sugar that usually occurs after a meal). Chlorogenic acid in particular, has been shown to reduce blood glucose in both animal experiments and human studies. Other components including lignans, quinides and trigonelline have also been proposed to improve glucose metabolism. It is likely that there is a ““synergic effect at play within the matrix of compounds that make up coffee.” In other words, a number of substances can work together to add to each others’ effects. It seems that these components work to improve fat cell function (perhaps by increasing adiponectin), liver function and reducing oxidative stress.
So Does My Kopi Count?
Depends. Not all coffee is created equal! These studies were carried out over various groups of people drinking different types of coffee (filter, espresso, instant etc.). But none of them mentioned including condensed or evaporated milk in the coffee!
In fact, the studies don’t really go into details about the effects of milk and sugar in coffee on the outcomes. However, we know enough about sugar and milk to know that choosing unsweetened black coffee or coffee with milk (or unsweetened milk alternatives), is always going to be the healthiest choice.
Best to get your Kopi O Kosong!
What if I Already Have Diabetes?
Hmm, good question. A systematic review of randomised controlled trials looked at the effects of caffeine or caffeinated drinks in people with diabetes. It found that caffeine had a negative impact on blood glucose levels and insulin sensitivity. Only one of these studies (and one from the 1960s!) had used coffee itself, the rest used caffeine supplements.
But, there’s more to coffee than caffeine, in fact, caffeine only makes about 2% of coffee! It’s kind of like taking the sugar out of fruit and seeing what it does to blood glucose levels! While this is important to know, it only gives us part of the picture. This is demonstrated by a study that showed that giving caffeine alone had 40% greater effect on blood glucose than the same dose of caffeine naturally present within a coffee beverage.
Two large studies found regular coffee consumption was not associated with increased risk of heart disease or death in diabetic men or women. Again, this is only observational evidence but researchers argue, that the consistent finding of a reduced risk across multiple studies and under meta-analysis indicates that this is a genuine phenomenon.
Two Very Interesting Studies about Coffee and Diabetes
One randomised, cross-over study looked at the short-term effect of drinking a black espresso coffee. They found this did not result in significant changes in glucose metabolism in those with diabetes. This is just one study, but we’d love to see more like this, looking at people actually drinking coffee!
On the flip side, researchers have conducted a pilot study where diabetic coffee drinkers abstained from coffee for three months. This significantly reduced their HbA1c. Again, this is just one small study and it lacked a control group. But it’s something to think about and look out for more studies on.
So if you have diabetes and are having trouble controlling your blood glucose levels, why not try cutting back on coffee or choosing decaf? See if this has any effect on your blood glucose levels. If it seems to help, keep it up until your next HbA1c and see if it makes a difference.
Death Before Decaf?
Speaking of decaf… As a Melbournian and an ex-barista who may or may not have cringed every time decaf was ordered, I hate to say it. The science is looking good for decaffeinated coffee.
One systematic review looking at coffee and diabetes found that decaf coffee decreased the risk of developing diabetes to a similar degree as caffeinated coffee.
But researchers argue the benefits may go even further than that. One experimental study found that decaf coffee reduced blood glucose levels and insulin resistance in mice. While adding caffeine to the decaf coffee prevented this positive outcome. Decaf coffee could be an important dietary component when combating insulin resistance. Think about it, all the benefits of the other compounds in coffee without the caffeine holding them back!
So to Coffee or Not to Coffee?
If you don’t have diabetes and your daily coffee is making you happy (and gets you out of bed in the morning!) it may be helping to prevent diabetes.
Before we start giving out nutrition prescriptions for coffee, we need more trials + a better understanding of what’s at play. The good news is, this a hot topic so we can expect to see more research soon.
If you do have diabetes and can’t get your sugars under control with a healthy diet and lifestyle, you could try cutting back on caffeinated coffee. Who knows, it might be the solution you’ve been looking for.
Lastly, we know that sleep is important in controlling blood glucose levels. As anyone who’s ever accidentally had too many coffees in the late afternoon knows, the two don’t always go hand in hand. Try to have those coffees early in the day or even switching to decaf (there I said it!).
*This article uses the term Diabetes to refer to Type 2 Diabetes Mellitus.