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Does Caffeine Affect Blood Sugar?

While some affirm the health benefits of caffeine, like improving insulin sensitivity and blood sugar, research is mixed on whether it's detrimental for people with diabetes.

Caffeine has been shown to offer a handful of health benefits, including potentially reducing the risk of developing type 2 diabetes. 

But for those who already live with diabetes, does caffeine offer similar benefits? It turns out there isn’t an easy answer to this question. Research is mixed on whether caffeine benefits those with diabetes, with some experts calling for more targeted studies before doling out certain dietary interventions

When in doubt, it’s best to speak with a healthcare provider about your caffeine intake, as everyone responds to it differently. 

How caffeine affects blood sugar

While we don’t definitively know whether a daily cup of coffee is helpful or harmful to those with diabetes, we do know that caffeine is a stimulant that has specific effects on the body. Most notably, caffeine stimulates the release of adrenaline and cortisol.

Adrenaline (the "fight or flight" hormone) can cause a temporary spike in blood sugar levels by promoting the breakdown of glycogen (stored glucose) in your liver and muscles. Similarly, elevated cortisol levels can lead to insulin resistance over time, potentially raising blood sugar levels in the long run.

However, some studies suggest caffeine might improve insulin sensitivity by allowing cells to use glucose more effectively. This could potentially help regulate blood sugar levels in some individuals. So, while caffeine does spike blood sugar levels in some cases, it also has the potential to improve one’s sensitivity to insulin over the long term.

Is caffeine healthy for people with diabetes?

The U.S. Food and Drug Administration (FDA) places a daily 400 mg limit on caffeine for “healthy adults” – roughly 4-5 cups of coffee.

For those with certain health conditions like diabetes, however, the FDA’s guidelines are unclear. Because diabetes affects everyone differently, some people with diabetes may be able to consume caffeine safely. Others may find that reaching for a decaffeinated beverage is a better choice.

Barbara Kovalenko, a registered dietician and nutrition consultant at Lasta, has many patients with diabetes and finds that the FDA’s guidelines are usually safe to follow. 

“People with diabetes can generally consume moderate amounts of caffeine. However, they still have to monitor how caffeine affects blood sugar levels,” she said. “I personally recommend staying within the FDA's recommended daily limit. Exceeding this limit may lead to side effects that could indirectly impact blood sugar management.”

Diabetes-friendly ways to consume caffeine 

If your healthcare provider has given you the all-clear to consume caffeine, you must keep in mind that different types of caffeinated beverages and foods have drastically different levels of caffeine. 

Let’s look at some of the more popular ways to consume caffeine and whether they’re safe for people with diabetes.


For those wondering if their morning cup of joe is safe to drink, it likely is.

One 2021 study that looked at the effects of coffee on insulin resistance and sensitivity found that “long-term caffeinated or decaffeinated coffee consumption does not negatively affect insulin resistance or sensitivity.” Researchers added that “there is no need to restrict coffee intake in [those with diabetes and prediabetes] for fear of insulin resistance.”

While these findings are promising, the study has notable limitations, including small sample sizes, the inability to control certain variables like diet and exercise, and not evaluating the effects of caffeine consumption beyond 24 weeks.

Ultimately, if you want to enjoy a daily coffee, drink it black and monitor your blood glucose levels to see how your body responds. You may find that you need to bolus for insulin beforehand, even if you aren't adding sugar or creamer.


Tea is a dietary staple for many worldwide, including people with diabetes. And, some teas may be beneficial for those with certain metabolic conditions.

Green tea, for example, is a caffeinated tea that provides many benefits, including potentially reducing all-cause mortality in those with type 2 diabetes. One five-year-long study that followed the health of over 4,000 participants with diabetes found that those who drank four or more cups of green tea daily experienced a 63% lower rate of death.

This is great news for people with diabetes who still want to consume caffeine but are wary of drinking coffee. Green tea has less caffeine per cup than coffee, so if your glucose levels spike after drinking coffee, it may be worth giving green tea a try. In fact, Kovalenko said that around 3-4 cups of unsweetened tea a day is likely safe for people with diabetes.

However, if you’d rather err on the side of caution, certain decaffeinated teas have also been shown to positively affect those with diabetes. 

One study on chamomile tea, a popular decaffeinated tea often used to promote sleep and reduce stress, examined how it affected insulin resistance and inflammatory markers in those with type 2 diabetes. Over eight weeks, the study found that the consumption of chamomile tea three times a day (after each meal) had beneficial effects on both these parameters.

Soft drinks

At one point or another in your health journey, you’ve likely been told to avoid sugary soft drinks and to consume their “diet” counterparts instead. But what about the caffeine in these diet soft drinks? 

The general consensus is that diet soft drinks are fine in moderation. For example, a standard 12-ounce Diet Coke has 46 mg of caffeine. A coffee of the same size has over three times that amount. 

Of course, moderation is key, as the artificial sweeteners in certain diet beverages have been shown to increase the risks of other medical conditions like heart disease.


Chocolate – especially dark chocolate – does have a small concentration of caffeine. But chocolate lovers can indulge in moderation.

While chocolate is relatively safe from a caffeine-intake perspective, you do need to pay attention to its sugar content. Milk chocolate contains less caffeine and more sugar. Dark chocolate has more caffeine and less sugar. 

“Chocolate with a higher cocoa content [i.e., dark chocolate] can be enjoyed in moderation – around 1-2 ounces (28-56 grams) per day,” said Kovalko.

If you’d rather avoid the sugar altogether, opt for a sugar-free dark chocolate product. In a 2022 study, researchers found that sugar-free dark chocolate sweetened with stevia, erythritol, and inulin “led to a lower blood glucose compared to the conventional dark chocolate bar in people with diabetes.” 

While more long-term studies are needed to back this claim, the research is promising. On the other hand, another recent study showed that elevated levels of erythritol and several related artificial sweeteners were associated with an increased risk of cardiovascular events. More research is needed on if these sweeteners are helpful or harmful to overall health.

Energy drinks

Energy drinks are often full of caffeine and sugar, making them less suitable for individuals with diabetes. Even sugar-free energy drinks may do more harm than good. 

A 2021 study looked at how mice responded to certain energy drinks over the span of 13 weeks. At the end of the study, mice that consumed sugar-free energy drinks had high blood glucose and triglyceride levels and showed signs of insulin resistance. The researchers concluded that consuming sugar-free energy drinks may “induce metabolic syndrome, particularly insulin resistance.”

If you need a quick jolt of energy, opting for a more natural caffeine source like black coffee or tea is better. 

The bottom line

Caffeine can affect your blood sugar levels, but research is mixed on whether it is detrimental to those with diabetes. Some people may be able to consume the FDA’s standard daily caffeine limit; others may not be able to tolerate a single cup of coffee. 

“To test how these products affect blood sugar, individuals can follow a systematic approach. Consume a controlled amount, monitor blood sugar levels before and after, and observe for any spikes,” Kovalko said. “This method, combined with regular monitoring and consultation with healthcare professionals, helps individuals make informed choices aligned with their health goals.”

Learn more about diabetes and managing blood sugar here: