Can Coffee Raise Blood Sugar? Caffeine, Diabetes, and More

Does caffeine lower blood sugar? How caffeine matters 

Some may think: that black coffee doesn’t contain any carbohydrates. So it shouldn’t raise blood sugar levels on its own.

Only 10% of coffee drinkers in the US had a cup of decaf the past day (1). Thus, when discussing coffee, the spotlight often falls on caffeine. However, coffee has other compounds that may cause it to interact differently than pure caffeine tablets. Some studies show coffee is protective against diabetes. So let’s focus on how caffeine affects blood sugar and diabetes.

Caffeine and insulin: What is the relation?

The truth is caffeine can affect how your body responds to insulin. Insulin is a hormone that helps take glucose (sugar) from the blood to the organ, thus reducing blood sugar levels (2). 

Caffeine alone could impair insulin sensitivity, as noted in many studies. (3, 4). That means your cells don’t react to the hormone as much as they once did. Hence, your insulin works less effectively, and sugar stays in your bloodstream (5).

In turn, after meals, these cells may not absorb as much sugar as they used to. Thus, it requires your body to secrete more insulin than it needs to help glucose enter the cells. The condition can lead to prediabetes (5).

So, what’s the real story behind the impact of caffeine on insulin?

The most common explanation is that caffeine can attach to and block adenosine receptors (6, 7). Adenosine helps us balance glucose (sugar) metabolism by controlling insulin secretion, glucose release, and absorption (8).

By binding to adenosine receptors in the body, caffeine can hinder the signals from adenosine, thus blocking the signal for glucose uptake. 

Moreover, when caffeine goes to your liver, it is mainly converted into paraxanthine. Paraxanthine is another strong blocker of adenosine. So even metabolized by our body, the effect of caffeine on insulin can still last long (6, 9).

Another theory suggests that caffeine intake may lead to a rise in stress hormones like epinephrine (or adrenaline). Epinephrine acts as an insulin antagonist and can prevent your cells from uptaking sugar in muscle and fat (10, 11).

Epinephrine also induces a surge in glucose production in the liver from its stored form (glycogen). So epinephrine has the opposite effect of insulin on glucose metabolism (11, 12). 

In one study, seven men drank one of four things before drinking a sugary drink: 

• A sugar pill (placebo)
• Caffeine
• Propranolol (a drug to block epinephrine)
• Caffeine and propranolol. 

The levels of epinephrine were higher in the caffeine tests. The men displayed decreased insulin sensitivity when they drank caffeine, but only when they didn’t take propranolol or when epinephrine worked well (13).

Besides directly influencing your blood sugar, caffeine can increase free fatty acid (FFA) production. This occurs due to more fat breakdown by increased epinephrine or by stopping adenosine (11).

High FFA levels can lower the amount of glucose uptake to organs and are also linked to lower insulin sensitivity (11).

Moreover, caffeine may keep you awake, which affects your sleep. Lack of sleep can also lower your insulin sensitivity (14).

A rise and drop in blood sugar and insulin is temporary; our body can help balance it in a few hours. Caffeine is still generally safe for healthy people to consume as long as it is not overused (10).

However, people with diabetes may have more concerns because their body already has trouble secreting insulin (type 1 diabetes) or don’t use insulin well (type 2 diabetes) (15, 16). 

In people with type 2 diabetes, drinking caffeine (around 200‒500 mg) is linked with a spike in blood glucose by 16‒28% and insulin by 19‒48% when taken before a glucose load. At the same time, caffeine decreased insulin sensitivity by 14‒37% (10).

Does caffeine raise blood sugar levels in type 2 diabetes?

The short answer is yes. Caffeine can significantly trigger a spike in blood sugar levels (17). Some people’s blood sugar is even extra sensitive to caffeine (14).

Even though exercise training can improve insulin sensitivity, study shows it failed to counteract the adverse effects of caffeine on glucose uptake, even in healthy people (18).

In a systematic review article, the authors concluded that caffeine has a negative impact on blood glucose control in type 2 diabetes. It doesn’t happen before eating, but from 1‒3 hours after eating sugar (10).

Several studies show people with type 2 diabetes who consume caffeine had significant blood sugar spikes after meals, with a quantity of 16‒28% higher after consuming caffeine versus placebo (4, 10, 15). 

However, many studies only examine the impacts of caffeine pills, not coffee or tea. 

In a study, stopping caffeine pills intake reduced glucose increases by 21% after a meal. So quitting caffeine for type 2 diabetics could be beneficial (15). 

Caffeine also makes it harder to uptake glucose, contributing to higher glucose levels throughout the day. The effects can last longer in those with type 2 diabetes (10, 19).

How about other components in coffee?

A small study in type 2 diabetics showed that the other components in coffee may not be protective of glucose spikes caused by caffeine. When caffeine pills were administered with decaf coffee, patients with type 2 diabetes had elevated glucose levels compared to those who drank only decaf coffee (20). 

If this happens every day, it can make it harder to control blood sugar in the long term (10, 20).

Some may think as this effect is momentary, your body would quickly become tolerant to caffeine. Yet this is just a theory. 

No link suggests that drinking caffeine causes tolerance to its effects on blood glucose. Regular caffeine consumption still causes high blood sugar levels in type 2 diabetes (10, 19).

The effect of coffee and caffeine on blood sugar levels can vary from person to person. To determine if caffeine or coffee increases your blood sugar levels, consult your doctor or a dietitian. 

You can also monitor your blood sugar levels before and after drinking coffee or refrain from caffeine for several days. 

Those who can digest caffeine quickly may be more prone to this adverse effect (4).  

Sip or skip: Is it okay to drink coffee with diabetes?

Globally, diabetes affects about 422 million people (21). If you turn to coffee every morning and have diabetes, remember that it may increase your blood sugar.

Many people with diabetes wonder whether they can still enjoy their daily coffee habit. The evidence suggests that coffee may impair glucose metabolism in persons diagnosed with type 2 diabetes. However, in healthy persons, it may not be harmful (7, 10).  

The Java effect: Coffee and Prediabetes

Prediabetes means your blood sugar is too high but not high enough to be called diabetes. It usually happens to people who already have some trouble with insulin (5).

Even causing short-term glucose spikes, coffee is still linked to a much lower chance of developing diabetes if it is regularly consumed (22, 23).

A study started with 88,259 women in the US who did not have diabetes. It found that drinking coffee for eight years lowered the risk of developing type 2 diabetes. Regular coffee was even slightly better than decaf (24).

Compared to those who didn’t drink coffee, the risk of getting diabetes was 13% lower for one cup per day, 42% lower for two to three cups per day, and 47% lower for four or more cups per day (24). 

Another study followed 1878 adults aged 20‒70 for about six years. People who drank at least one cup of coffee a week were 27% less likely to have prediabetes and 34% less likely to have type 2 diabetes (25).

The main reason behind this can be the chlorogenic acid in coffee. This antioxidant can benefit glucose metabolism by reducing inflammation, improving insulin sensitivity, and fostering insulin secretion (26). 

Scientists have studied chlorogenic acid as a potential treatment for type 2 diabetes (27, 28, 29). 

Caffeine and diabetes type 1 

Hypoglycemia (low blood sugar) is a common phenomenon with type 1 diabetes. People who worry about rising blood glucose spikes may try to eat less sugar (10). 

Hypoglycemia warning signs include feeling hungry, trembling, sweating, and anxious. It can even lead to losing vision, coma, and death (30).

In a study of 34 patients with type 1 diabetes, they provided caffeine pills to the patients and saw increased symptomatic hypoglycemia warning symptoms (31). 

This phenomenon does not affect standard glycemic control (measured by HbA1c) or cause more severe episodes (31).

Another study showed a decrease in nighttime hypoglycemia episodes at the expense of an increase in daytime mild hypoglycemic episodes (32). 

Some other studies revealed that consuming 400‒500 mg of caffeine can help reduce the length of hypoglycemic episodes and improve awareness of hypoglycemia in type 1 diabetes (10).

Yet the available studies are small-scale, raising the need for further research.  

The best coffee for diabetics

Black coffee can be consumed by those with diabetes as long as there is no added sugar. Still, you should be careful of the caffeine content: Moderation is always the key.

No matter what coffee brands tell you, coffee always contains caffeine (even decaf!). So, the best coffee comes from your favorite brand and is customized by you. 

What can diabetics put in their coffee? If you have diabetes and rely on coffee to get through the day, don’t add sweeteners or other sugary things (33).

Added sugar may pose a strain on your body to produce and use more insulin to clear sugar from the bloodstream (14).

Also, some may love the flavor and creaminess of creamers in their coffee, but they are often loaded with fat and sugar. 

Instead, you can choose plain reduced-fat or fat-free milk (without added sugar) or plain oat, cashew, hazelnut, or almond milk beverages. They are rich and creamy without guilt. 

Plus, why not use natural flavorings? Extracts, fruits, and spices can all add deliciousness to your cup of joe.

Citrus (lemon, lime, or orange) can go well with coffee. Spices like cinnamon, ginger, and turmeric are other great options.

If you’re worried about caffeine hurting your blood sugar, try drinking coffee after eating. Your body also gets other nutrients like protein and fiber, which help lower spikes in blood sugar.

Which is better for diabetics, tea or coffee?

Drinking three to four cups of coffee every day was linked with a lower risk of diabetes, heart disease, and some cancers. However, this amount may be too high for some persons (34). It’s time for some alternatives out there. 

The beneficial chlorogenic acid is not a unique component of coffee. You can easily get it from many fruits and vegetables (35). 

Tea is another good alternative. Tea and coffee contain caffeine, but coffee generally has higher caffeine levels (36, 37).

Tea is considered to have a minimal impact on blood sugar levels. Tea also has antidiabetic compounds like flavonoids (a group of antioxidants) content (38). 

The main antioxidants in tea are catechins, which can help regulate glucose uptake in the gut (39). It may help your body manage blood glucose balance and homeostasis.

Previous studies have also indicated that green tea may improve glucose control and insulin sensitivity. Yet few studies have looked into the potential benefits of green tea for those with diabetes until now (40, 41).

There is not yet enough clinical evidence to say if coffee or tea is better for people with diabetes. Still, tea contains less caffeine and shows little evidence to impact your blood sugar levels.  

Can stress raise blood sugar?

Stress can make it harder for those with diabetes to manage their blood glucose levels, especially for the young with type 1 diabetes.

Stress and A1c: From mind to body

A1c is a measure of long-term blood sugar control. If you have diabetes, it’s vital to keep your A1c levels low (17, 42).

Sugar in your blood attaches to hemoglobin (Hb) in your red blood cells. The A1c levels reveal the percentage of your red blood cells with sugar-coated hemoglobin (HbA1c). Thus, it predicts your diabetes risk (42).

People who experience both acute and chronic stress (especially with diabetes) tend to have higher A1c levels, according to many studies. This is specifically true for groups that face extra stress, such as young adults (43, 44, 45).

Also, stress can come from diabetes itself (46). When examining the relationship between diabetes-related distress and A1c, two main patterns have been noticed (45):

• The initial level of diabetes-related stress does not predict changes in A1c, and vice versa.
• Decreases in diabetes-related stress may be linked to a drop in A1c levels. 

However, everyday stressful events that often last only a few minutes or occur a few hours before testing do not affect A1c. So the impact of long-term stress on A1c can be more significant than what scientists have found. 

Stress and glucose levels: Unveiling the connection

Can stress cause high blood sugar? Unfortunately, the answer is yes, and this condition is called stress hyperglycemia (47). 

It happens for many reasons, including hormone changes, blood sugar regulation, and insulin signaling (47). 

Plus, stress can provoke inflammation, a less common cause of high blood sugar (47). 

If you have type 1 diabetes, worrying about hypoglycemia can drive stress. That creates a vicious cycle of stress and climbing blood glucose levels (48, 49). 

The mechanism behind it is complex, but stress may badly affect your condition.

While many studies found that stress can raise diabetes risks, there are ways to manage the stress that can help with glycemic control (17, 46, 48). Defining the root cause of your stress is vital.

What is considered a blood sugar spike? Decoding the threshold

A blood sugar spike occurs when your blood sugar levels rise rapidly. This can happen after eating a meal high in carbohydrates or sugar. Sometimes, it’s a side effect of certain medications, stress, or sickness (50). 

Some may wonder what happens when blood sugar spikes. You may feel tired or thirsty, have blurry vision, and need to urinate (pee) more often (17, 50).

You can check it simply with a blood glucose test. You might have diabetes if (51): 

• Your blood glucose is greater than 125 mg/dL while fasting
• Your blood glucose is greater than 180 mg/dL 2 hours after eating

A spike often falls after some hours in healthy people. But with diabetics, it could be a problem. 

When blood sugar levels heighten rapidly, our body produces insulin to help transport glucose into cells for energy. Yet these insulin spikes can foster a drop in blood sugar levels. In such a manner, hypoglycemia occurs (30).

Over time, repeated blood sugar spikes can damage the blood vessels and nerves, leading to heart, brain, and kidney diseases (51).

Therefore, keeping your blood sugar levels in the target range is vital because it helps prevent or delay long-term, serious health problems and improves energy and mood (17).

Can dehydration cause high blood sugar?

When your body loses its necessary water, blood sugar is more concentrated. It will, of course, raise blood sugar content (14, 52).

Also, dehydration may make you urinate less. Consequently, sugar can’t be excreted and stays in your bloodstream. 

Moreover, a dehydrated body will produce higher levels of the hormone vasopressin (52). Vasopressin is known to cause insulin spikes, which can further contribute to lower insulin sensitivity (53, 54).

There is also a possible link between dehydration and low blood sugar because insulin spikes can lead to hypoglycemia in a short period (30). Yet, these theories need further human trials to be confirmed. 

People with diabetes should be more aware of the importance of drinking enough water. Severe dehydration can cause serious problems like coma and blood clots in the brain, in this case (55).