Coffee, tea, and caffeine: How they affect glucose

Published: Oct. 7, 2025

3 min read

Table of contents

The content in this article should not be taken as medical advice. Please consult with your healthcare provider regarding your individual health needs.

For many of us, mornings (and sometimes afternoons) start with coffee, tea, or another caffeine fix. And while caffeine can certainly perk you up, it can also affect your glucose levels. This may mean a short-term spike, but it could also have longer-term impacts. It all depends on what you stir into the cup.

Here are the main things to know about how caffeine interacts with glucose, and how to make sure it works with your health goals.

checking glucose readings on phone while eating breakfast

Caffeine 101: Why your glucose levels might rise after a cup

Caffeine gives you energy in part by making your body a little less sensitive to insulin and by prompting your liver to release stored glucose. That’s why some people see a spike in glucose even when drinking black coffee or unsweetened tea.

The response is highly individual. Some see no change while others notice a spike, especially if caffeine is paired with a carb-heavy meal. Side effects like poor sleep, jitters, or digestive issues can also indirectly impact glucose.

And so how much is too much? For most adults, up to about 400 mg of caffeine per day (roughly 2–3 small cups of brewed coffee) is considered safe, though sensitivity varies widely. If you’re curious, try wearing a glucose biosensor like Stelo and compare your glucose after the same meal with and without caffeine.

Coffee and glucose: The short vs. long view

In the short term, caffeine may spike your glucose levels because it can make your body less sensitive to insulin. But here’s the bigger picture: research from American Diabetes Association suggests that people who drink coffee daily—about two to five cups (regular or decaf)—actually have a lower risk of developing certain health conditions like type 2 diabetes. This may be because your body gets used to caffeine’s effects, so those early glucose spikes fade as you build tolerance. Plus, coffee is packed with antioxidants and helpful compounds that may protect your health in ways that go beyond just the caffeine.

Pro tip: Remember to watch the extras. Sugar, flavored syrups, and heavy creamers can quickly turn coffee into a glucose-spiking dessert.

Teatime: Green, black, and beyond

Tea generally delivers less caffeine than coffee (about 40 mg in a cup of green, 70 mg in black, vs. ~110–250 mg in coffee). For some people, that lower dose alone makes tea gentler on glucose.

Green tea in particular has been linked to small reductions in fasting glucose and A1C, while black tea polyphenols may help blunt post-meal spikes. The effects are modest but meaningful if tea helps replace sugary drinks.

Of course, you’ll want to stick to unsweetened versions. Sweet tea and bottled “iced teas” can contain as much sugar as soda.

Caffeine-free options

If you love the ritual of a warm cup but want to skip the buzz, there are plenty of satisfying alternatives.

1. Decaf coffee

Keeps the flavor, dials down the caffeine, and still delivers beneficial compounds.

2. Herbal teas

Teas like rooibos, chamomile, and peppermint are naturally caffeine-free and soothing, especially in the evening.

3. Chicory or roasted grain drinks

Coffee-like flavor without the caffeine (but check labels for added sugar).

Smart sipping tips

Here are a few things to keep in mind:

Time it right: If caffeine tends to raise your glucose, consider pairing your morning cup with a meal rich in protein and healthy fats, and fewer fast-acting carbs like cereal or pastries. Or, try sipping coffee after you eat—timing and balance can make a real difference for your glucose response.
Tweak the dose: Try half-caf, smaller cups, or switch to tea/decaf later in the day.
Mind the mix-ins: Keep drinks unsweetened or low-calorie most of the time.
Test your own response with Stelo: Everybody’s glucose response is unique, which makes tracking your patterns with Stelo especially valuable. Notice how your glucose shifts after different drinks over time.

woman walking with headphones on holding up her phone

Keep brewing healthy habits

Caffeine can raise glucose in the short term, though not for everyone. At the same time, coffee and tea (when unsweetened) are frequently linked with long-term benefits. With a little awareness (and smart choices about what goes in your cup), coffee, tea, and caffeine-free alternatives can fit right into a glucose-friendly lifestyle.