Coffee & Caffeine Good or Bad for Diabetes? Blood Sugar + Insulin Effects

Diabetes is one of the top ten causes of death for Americans (1)​.

Approximately 1.4 million people in the U.S. are diagnosed with the condition every year.

Almost 10 percent of the American population has type 2 diabetes.

Some researchers predict that 65 percent of people across the globe will have the condition by 2025 (2).

If you’re a coffee drinker, you might be in luck. Coffee has been associated with a decrease in type 2 diabetes risk (3, 4).

The Coffee Controversy

The information that’s out there about coffee can be confusing.

A quick internet search will result in a variety of information regarding coffee’s benefits and detriments to your health.

Some health gurus tell you to quit drinking coffee if you care about your wellbeing (5).

In the short term, however, drinking coffee can increase your blood sugar and hinder your body’s ability to metabolize glucose (6, 7, 8).

If you’re worried about developing diabetes, should you drink coffee, or should you avoid it?

We have explored the facts behind coffee and diabetes and spelled them out for you below.

KEY POINT: Some people claim that coffee is good for your health, while others warn against drinking it.

​How Blood Glucose Levels Affect Diabetes Risk

Woman taking diabetes test close-up of hands

Fasting glucose levels, glucose regulation and glucose tolerance are associated with type 2 diabetes.

In other words, the way that your body uses sugar for energy can increase or decrease your risk of developing type 2 diabetes (9).

Fasting glucose levels refer to the amount of glucose in your blood after you have avoided food or beverages for 8 to 12 hours.

Glucose regulation and glucose tolerance indicate how well your body processes sugar in order to use it as an appropriate source of energy.

Glucose tolerance indicates how well your body processes large amounts of sugar (10).

Insulin resistance is another phrase for glucose tolerance.

Insulin is a hormone that the pancreas makes to help cells throughout the body use glucose for energy (11).

Normally, as insulin is released into the bloodstream, it helps cells absorb that sugar. This reduces the amount of glucose in the bloodstream.

If you’re insulin resistant, the cells don’t respond to that insulin production. That means that they don’t absorb the glucose as readily.

That leaves more sugar in the bloodstream and puts you at a greater risk of diabetes and other health conditions.

KEY POINT: High blood glucose levels and insulin resistance are associated with an increased risk of type 2 diabetes.

​Drinking Coffee Reduces Your Risk of Developing Type 2 Diabetes

Coffee has been found to benefit blood glucose levels and insulin sensitivity (12)​.

Many studies have shown that drinking coffee reduces the risk of type 2 diabetes.

Is this a function of the caffeine? Some experts say no (13, 14).

woman thumbs up with coffee cup

One study found that coffee and black tea drinkers had a lower risk of developing diabetes than people who didn’t drink these beverages (15)​.

This study also found that drinkers of green tea don’t get the same benefits when it comes to type 2 diabetes.

Although it’s not clear from the study, this could indicate that the caffeine does play a part in the health benefits.

One meta-analysis determined that both caffeinated and decaffeinated coffee lowers diabetes risk.

However, caffeinated coffee is more effective (16).

The more coffee you drink, the more you reduce your risk of type 2 diabetes.

People who consume four to six cups of coffee on a daily basis are less likely to develop type 2 diabetes than people who only consume two cups per day (17).

KEY POINT: People who drink more coffee have a lower overall risk of developing type 2 diabetes.

​Drinking Coffee May Increase Blood Sugar Temporarily

Although coffee can lower your risk of diabetes, it can increase your blood sugar in the short term.

Insulin sensitivity is healthy.

It means that your body is reacting appropriately to the amount of insulin that’s naturally secreted into your bloodstream.

One study found that drinking what equates to a moderate amount of caffeine lowered reduced insulin sensitivity.

coffee beans in cup

That is, it increased insulin resistance (18).

This effect may be a result of the increased catecholamine levels caused by caffeine consumption.

This study found that many people adapt to caffeine’s effects on insulin sensitivity.

Although they may become insulin resistant initially, many will develop a tolerance to caffeine.

However, the tolerance could be dependent on the amount of time that it takes for the caffeine to be eliminated from the system.

Many studies look at the results after administering unnaturally large doses of caffeine to subjects at one time.

That led researchers to look at the effects of a single, average serving of coffee on blood sugar.

This study involved giving participants the equivalent of one serving of instant coffee.

The researchers found that even this typical dose negatively affected blood glucose levels in overweight men who were otherwise healthy (19).

Other studies have found that caffeinated coffee can cause spikes in blood sugar levels in people with and without type 2 diabetes (20, 21)​.

However, many studies that link caffeine with temporary blood sugar surges are using isolated caffeine, not coffee.

When you look at the effects of coffee on blood sugar, it is not as significant as the effects of caffeine alone (22).

This could be due in part to the other beneficial compounds found in coffee (23)

Glucose spikes are not often found when people consume decaffeinated coffee.

This further supports the idea that it’s the caffeine that is responsible for the undesirable glucose response (24, 25, 26)​. 

In these studies, although glucose levels increased, insulin resistance was not detected.

KEY POINT: Caffeine can increase your blood glucose levels temporarily.

However, regular coffee drinkers develop a tolerance to this effect.

Other ingredients in coffee can balance out unwanted effects on glucose levels.

​Does It Matter If You Drink Coffee Regularly?

Some experts have found that habitual coffee drinkers don’t get spikes in glucose and insulin levels (27, 28)​. 

serving coffee

In addition, as we mentioned before, several studies link coffee consumption with a decreased risk of type 2 diabetes.

How is this possible if drinking coffee can boost your blood sugar levels?

Coffee is full of antioxidants. In one study, two of the antioxidants found in coffee, chlorogenic acid and caffeic acid, were isolated (29).

Tests were done to determine whether these antioxidants could prevent cell damage from lipid peroxidation, cell damage caused by free radicals.

Although the antioxidants alone didn’t seem to have an effect on lipid peroxidation, coffee did have antioxidant effects on blood plasma and liver cells.

People who drink coffee regularly may benefit from these antioxidant properties.

One study set out to look at the effects of long-term coffee drinking on the risk of developing type 2 diabetes (30)​.

During the study, subjects either drank five cups of caffeinated coffee, five cups of decaffeinated coffee or no coffee every day for about four months.

Their blood glucose was measured before beginning the study, at eight weeks and at 16 weeks.

Blood glucose was measured after fasting as well as during a glucose tolerance test.

During the glucose tolerance test, participants were given a sugary beverage, and their blood glucose levels were measured in regular increments following the ingestion of the drink.

The people who drank caffeinated coffee showed no change in blood sugar levels after eight weeks.

However, they showed a drop in glucose levels during the glucose tolerance test after 16 weeks.

No changes were observed in the other groups.

If you’re a regular coffee drinker, you are more likely to be protected by coffee’s health benefits.

If you’ve just recently started drinking coffee, you might see an increase in your glucose levels before they decrease.

KEY POINT: Regular coffee drinkers don’t usually experience a surge in glucose levels.

Their blood glucose levels may actually fall after several months of habitual coffee consumption.

​Does Decaffeinated Coffee Reduce My Risk of Diabetes?

Researchers have demonstrated that both caffeinated and decaffeinated coffee have been linked with a lower risk of type 2 diabetes​ (31, 32, 33, 34)​.

hands hold cup of coffee

In addition, decaffeinated coffee doesn’t temporarily increase blood glucose levels (35, 36)​. 

Drinking caffeinated coffee along with a meal can impair your insulin sensitivity and make it harder to manage blood sugar levels.

This occurs whether or not the meal has a high glycemic index.

The same results have not been seen when people drink decaffeinated coffee with meals​ (37).

Decaffeinated coffee doesn’t increase blood sugar levels any more than water does.

In the long term, it does lower the risk of type 2 diabetes, however.

Decaffeinated coffee might be a good alternative for those who are just beginning to drink coffee.

It can also be an ideal choice for people who already have type 2 diabetes but experience a surge in blood sugar after drinking caffeinated coffee.

KEY POINT: Decaffeinated coffee has similar beneficial effects as caffeinated coffee when it comes to lowering type 2 diabetes risk, and it won’t temporarily increase blood sugar levels.

​What Compounds in Coffee Are Responsible For Lowering Your Diabetes Risk?

The studies that have looked into coffee consumption and diabetes can be confusing. Increased blood sugar is associated with an increased risk of type 2 diabetes.

Therefore, how can drinking coffee lower your risk of this health condition?

cup coffee beans

Experts aren’t exactly sure how the compounds in coffee lower the risk of type 2 diabetes.

Looking at the effects of coffee on different systems in the body can help explain this.

Coffee is a stimulant. It influences the release of catecholamines in the body, including epinephrine.

Epinephrine can quickly increase blood glucose levels (38).

Caffeine is an adenosine receptor antagonist. That means that it blocks adenosine receptors (39).

Adenosine is a neurotransmitter that is responsible for locomotor activity.

When the receptors are blocked, the muscles may have trouble pulling glucose from the blood (40, 41).

Adiponectin plays a part in insulin resistance. People with more body fat and type 2 diabetes have lower adiponectin levels.

Increasing your adiponectin can improve your insulin sensitivity and lower your blood glucose levels (42).

People who drink coffee regularly tend to have higher levels of this protein (43)​.

Sex hormone binding globulin (SHBG) has often been considered a marker for type 2 diabetes risk (44).

One study compared SHBG levels in women who drank four or more cups of coffee a day with those of women who didn’t drink coffee.

The coffee drinkers had higher levels of SHBG. Tea and decaffeinated coffee weren’t associated with higher SHBG levels (45).

hands holding coffee with heart shape topping

Studies have consistently shown that temporary increases in blood sugar levels are associated more with caffeine than with coffee (46, 47, 48).

This suggests that other compounds in coffee can negate the negative effects of caffeine.

Roasting coffee beans releases quinides, which have been shown to change blood sugar levels (54​). 

Drinking coffee can also balance intestinal peptides. These hormones help manage fullness and insulin secretion.

The prebiotic qualities of coffee can improve digestion, which in turn may improve glucose levels (49).

Many components in coffee have anti-inflammatory properties.

This can help reduce oxidative stress and protect against the risk of type 2 diabetes (50).

Coffee has also been associated with improved liver health.

Because the liver is involved in digestion and glucose metabolism, this association may be partly responsible for the reduced diabetes risk (51, 52).

KEY POINT: Coffee has several properties that may be responsible for its ability to decrease your risk of type 2 diabetes.

​Bottom Line

There are many hypotheses as to why coffee drinkers may have a reduced risk of type 2 diabetes.

Although studies show that coffee can increase blood glucose levels initially, regular drinkers develop a tolerance and benefit from many of coffee’s health-boosting properties.

Everyone reacts differently to coffee (53)​. 

If you already have type 2 diabetes, you need to be vigilant about your blood glucose levels in response to coffee consumption.

In addition, you should be careful about drinking specialty coffee drinks or adding sugar to your beverage.

Unless you have a medical condition for which a surge in blood glucose levels would be problematic, drinking coffee on a regular basis can help lower your type 2 diabetes.

For the average individual, the health benefits of coffee outweigh the risks.

That doesn’t mean that you can down a few mugs when you wake up and then follow an unhealthy lifestyle, however.

You should also exercise and eat a healthy diet.

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  • Updated August 27, 2018

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