Key Takeaways 

• Coffee consumption raises blood glucose levels acutely but exerts protective effects against type 2 diabetes (for individuals without T2D) and possibly lowers mortality risk (for individuals with T2D) in the long term.

• Scientists hypothesize that, over time, the beneficial effects of coffee’s bioactive compounds — such as CGA — dominate over caffeine’s hyperglycemic effects.

• The current body of evidence suggests that it’s safe for individuals with diabetes to drink coffee.

• That said, you should ideally keep your daily caffeine intake below 400 mg and choose types of coffee that are relatively low in added sugar (e.g., kopi o kosong instead of kopi).

 Coffee: (n.) survival juice.

 If you relate to that, you’re probably one of the many Singaporeans contributing to the country’s impressive coffee consumption of 15,000 metric tonnes, or roughly 2.6 kg of coffee per capita, yearly.

But here’s some food for thought. As effective as coffee is for:

• Wiping out the morning bleariness in your eyes, and

• Resuscitating you from the dreaded afternoon slump

… should you even be drinking it in the first place especially if you have diabetes? Because what if it's messing up your blood sugar levels? Continue reading to learn how your coffee consumption impacts diabetes and what you could do about it. 

How does coffee affect blood sugar?

Does coffee raise sugar? Lower blood sugar?

Unfortunately, there’s no cut-and-dried answer to how coffee impacts blood sugar levels.

Individuals without diabetes

Let’s first talk about individuals without diabetes. A large body of evidence, including this comprehensive 2018 meta-analysis published in Nutrition Reviews, shows an inverse relationship between coffee consumption and the risk of type 2 diabetes (T2D).

I.e., the more coffee an individual drinks, the lower their risk of developing T2D.

Given this, coffee should have a beneficial effect on blood sugar levels … right? Well, studies say no.

Several studies have shown the opposite — specifically, that in individuals without diabetes, coffee consumption increases insulin resistance and blood glucose concentration.

Further muddying the waters is this: a 2019 systematic review published in the Journal of Traditional and Complementary Medicine. After analyzing eight clinical trials, the researchers found that coffee consumption could improve glucose metabolism in the long term.

Individuals with diabetes

In case you’re wondering, the picture doesn’t get any clearer for individuals with diabetes.

According to a 2013 systematic review published in the Journal of Human Nutrition and Dietetics, trials in individuals with T2D demonstrated that the ingestion of caffeine (approximately 200 to 500 mg) significantly increased blood glucose concentrations by 16% to 28% of the area under the curve or AUC.

FYI, AUC measures how long your body takes to use or store glucose after a meal; the greater the area, the longer it takes for your blood glucose levels to return to pre-meal values.

OK … but those were short-term studies.

So, would long-term coffee benefit glucose metabolism for individuals with diabetes (as it did for individuals without)?

As of now, we still don’t know.

There's a shortage of research investigating coffee's long-term impact on blood sugar levels in people with diabetes. But what we do know is that coffee appears to have at least a neutral or possibly protective effect on mortality for those with T2D:

• 2018 study published in Frontiers in Endocrinology: Found a dose-dependent protective effect of caffeine consumption on mortality among women with diabetes. I.e., women with diabetes who consumed caffeine from coffee had a reduced risk of all-cause mortality. This association was not found in men. 

• 2023 meta-analysis published in the BMJ: Found an association between consuming high amounts of coffee (defined as four cups daily) and lower mortality (26% lower risk of early death) in individuals with diabetes.

What’s with the scientific literature?

Coffee raises blood glucose levels acutely — but improves glucose metabolism (for those without T2D) and possibly lowers mortality risk (for those with T2D)?

How can we reconcile those two opposing ideas?

Scientists have floated a few theories. In the acute sense, they believe caffeine consumption raises blood glucose levels by:

• Acting as an adenosine receptor antagonist, blocking glucose uptake into muscle cells (even in the presence of insulin)

• Elevating epinephrine (adrenaline) levels, which may impair glucose uptake in peripheral tissue and stimulate hepatic glucose production (i.e., the production of glucose by your liver)

As for coffee's beneficial effects in the long term?

Researchers believe prolonged exposure to coffee gives more time for the bioactive compounds of coffee to exert their antioxidant and anti-inflammatory effects, which could improve glucose metabolism.

"Bioactive compounds" sounds vague. Which compounds are we talking about, exactly?

While there are a few, a notable one you should know by name is chlorogenic acid (CGA), the main phenolic component in coffee.

In animal models, the consumption of CGA enhanced insulin sensitivity and reduced fasting plasma glucose.

Should you drink coffee when you have diabetes?

Against the backdrop of everything discussed thus far, it appears safe for you to drink coffee, even if you have diabetes.

But it’s not the more, the better. This 2021 study published in Nutritional Neuroscience, for example, found that the consumption of > 6 cups of coffee daily was associated with 53% higher odds of dementia compared to the consumption of 1 to 2 cups daily.

So, where’s the line between reaping the health benefits of coffee and taking it too far?

The Food and Drug Administration (FDA) recommends people cap their daily caffeine intake at 400 mg. That typically translates to about four to five cups of coffee.

Also, perhaps a more critical point is that not all coffees are made equal. Think about it: a caramel latte will contain more added sugar than black coffee, which will raise your blood sugar levels more than the latter.

And on that note …

What types of coffee should people with diabetes drink?

In general, you should strive to drink coffee with minimal added sugars.

While the exact amount of sugar that’s safe to consume varies based on your specific situation, the American Heart Association recommends the following limits:

• Men: 36 grams (9 teaspoons)

• Women: 25 grams (6 teaspoons)

However, this begs the question: how would you know how much sugar is in the coffee you're eyeing?

Use the Nutri-Grade labels as guidance

You could get a rough gauge by looking at its Nutri-Grade label.

As part of Singapore's war on diabetes, the Ministry of Health (MOH) has instituted mandatory nutrition labels — aka "Nutri-Grade" — that "grade" drinks based on their sugar and saturated fat content, with "A" having the lowest levels and "D" the highest:

• A: ≤ 1 g sugar, no sweetener, and ≤ 0.7 g saturated fat per 100 ml

• B: > 1 to 5 g sugar and > 0.7 to 1.2 g saturated fat per 100 ml

• C: > 5 to 10 g sugar and > 1.2 to 2.8 g saturated fat per 100 ml

• D: > 10 g sugar and > 2.8 g saturated fat per 100 ml

You can find Nutri-Grade marks on packaged beverages (e.g., bottled, ready-to-drink coffee), powders or concentrates (e.g., instant coffee), and freshly made beverages from F&B outlets (e.g., coffee from Starbucks).

Note that drinks graded Nutri-Grade C and D must display the Nutri-Grade mark; on the other hand, Nutri-Grade labeling is optional for drinks graded "A" and "B".

What does this mean for you? Avoid drinking coffees sporting Nutri-Grade labels of “C” and “D” whenever possible.

Ordering coffee from smaller businesses

But there’s a catch.

Smaller F&B outlets are exempted from the mandatory Nutri-Grade C and D labeling if they:

• Earn a revenue of not more than S$1 million in the latest financial year and

• Sell or supply those drinks at fewer than ten food premises

Safe to say, it’s highly likely the humble kopi stall in the neighborhood hawker center hasn’t met those milestones. So, how would you know the total sugar damage your intended choice of coffee would do? Here's a nifty little table adapted from the Straits Times:

Drinks (in Singaporean term)

• Kopi

  What it means: Black coffee, sugar, and condensed milk

  Total sugar (g): 22.5

• Kopi c

  What it means: Black coffee, sugar, and evaporated milk

  Total sugar (g): 18.25

• Kopi siu dai

  What it means: Black coffee and condensed milk, less sugar

  Total sugar (g): 16.25

• Kopi kau

  What it means: Extra black coffee, sugar, and condensed milk

  Total sugar (g): 22.5

Now, you’re probably wondering, what about anything “kosong”? As a rule of thumb, adding a “kosong” (i.e., no sugar) to the back of your order will cut down your sugar intake relative to the original drink (e.g., kopi kosong will contain less sugar than kopi).

But if you’re wondering:

Is kopi o kosong healthy?

While it is technically black coffee with no added sugar, local kopi is made with Robusta coffee beans roasted with sugar and margarine. Strictly speaking, this means kopi o kosong isn't quite as healthy as black coffee made from beans with no sugar or margarine added to the roasting process.

Is kopi c kosong healthy?

Even with sugar out of the equation, kopi c kosong still contains evaporated milk, which contains more carbohydrates, fat, and calories than whole milk (which you’d find in a latte). Still, it’s relatively healthier than kopi kosong (black coffee and condensed milk) since condensed milk is much sweeter than evaporated milk. I.e., ordering the drinks from most healthy to least will be the latte, kopi c kosong, then kopi kosong.

Of course, proper diabetes control goes far beyond simply managing your total caffeine intake and making sugar-wise coffee choices. You'll also need to account for (doctor-prescribed) medication and lifestyle changes, which span eating, exercise, and supplements.

If you’d like to stay on top of all those and feel in control of your diabetes instead of feeling overwhelmed, check out NOVI Magnum.