Coffee is known for its energizing effects, and research has linked it to a lower risk of chronic conditions like heart disease and certain cancers. But how does it affect blood sugar? Here’s what experts say.
One of the ways coffee influences blood sugar is through the caffeine it contains, Catherine Metzgar, PhD, RD, a registered dietitian and director of coaching at Virta Health, told Health.
Here’s how it works: Caffeine triggers the nervous system’s fight-or-flight response and stimulates the release of the stress hormones cortisol, epinephrine, and norepinephrine. These hormones signal the liver to release stored glucose into the bloodstream, causing a temporary rise in blood sugar.
“At the same time, caffeine can lower the cell’s response to insulin, so the cells don’t use blood sugar as efficiently, leaving more in the bloodstream,” Michelle Routhenstein, MS, RD, CDCES, CDN, a registered dietitian focused on preventive cardiology nutrition, told Health.
This short-lived effect on blood glucose and insulin levels is most evident in non-habitual coffee drinkers, Dorothea Schlesinger, MD, a Berlin-based endocrinologist who specializes in metabolic and hormonal health, told Health.
For regular coffee drinkers, however, long-term consumption actually appears to benefit blood sugar. Some research reviews have found that people who drink moderate amounts (about three to four cups a day) of either caffeinated or decaf coffee have up to a 25% lower risk of developing type 2 diabetes compared to those who drink two or fewer cups daily.
“This likely reflects improved insulin sensitivity, modulation of oxidative stress, and the contribution of bioactive polyphenols, such as chlorogenic acids—compounds present in both caffeinated and decaffeinated coffee,” Schlesinger said.
Coffee’s influence on blood sugar isn’t just about caffeine—other factors play a role, too: Here are some of them:
- Whether additives are used: Sugar, flavored syrups, and sweetened creamers add carbohydrates and calories that can significantly raise blood sugar, especially for those who drink multiple cups a day, Metzgar said.
- When you drink coffee: Circadian rhythm and cortisol levels can affect coffee’s metabolic impact, Schlesinger said. Drinking coffee in the morning generally leads to smaller glucose bumps compared to the afternoon or evening, when insulin sensitivity is naturally lower.
- If you drink coffee on an empty stomach: “Drinking coffee first thing in the morning on an empty stomach can cause blood sugar levels to rise due to morning cortisol and faster absorption rate,” Routhenstein said. Drinking coffee after breakfast, on the other hand, can help buffer the blood sugar response.
- Your individual response to caffeine: Genetics, caffeine sensitivity, sleep quality, stress, and overall lifestyle can all influence how coffee affects an individual’s blood sugar, Metzgar explained.
For most people, small blood sugar changes from coffee aren’t cause for concern, Metzgar said.
Routhenstein agreed: “Having 8 to 16 ounces—one or two standard cups—per day is usually well-tolerated for most people,” she said. “What matters most is how much caffeine you consume, what you add to your coffee, and what else you’re eating.”
That said, people with prediabetes or diabetes may want to be a bit more mindful about their consumption. “These spikes can make blood sugar management more challenging,” Routhenstein explained.
Even so, these temporary spikes don’t appear to have lasting effects. “There is no evidence that moderate regular coffee consumption worsens long-term glycemic control,” Schlesinger said.
If you’re concerned about how coffee impacts your blood sugar, both Routhenstein and Metzgar said using a glucose meter or continuous glucose monitor can show you how your body responds to caffeine.
But when it comes down to it, your focus shouldn’t solely be on coffee. What’s most important, Metzger said, is “to look at your overall eating pattern and how all the pieces work together to support good health.”
