Caffeine May Affect Blood Glucose Levels

A small study conducted at Duke University has suggested that caffeine may hurt blood glucose control in people with Type 2 diabetes. The study’s authors have suggested that people with diabetes may want to avoid caffeinated beverages based on these findings; however, not all medical experts agree that total avoidance is necessary.

The study, which was published in the February issue of the journal Diabetes Care, looked at 10 people with Type 2 diabetes, average age 63. These people were all regular coffee drinkers before the study started and treated their diabetes with diet, exercise, and oral medicines, but not insulin.

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The researchers gave the study participants identical packets of pills to take with breakfast and lunch for two days. One day’s pills contained the amount of caffeine present in four cups of coffee, while the other day’s pills were placebos (inactive pills). The participants did not know which pills they were taking on which days and did not consume any other caffeine during the study.

The researchers used continuous glucose monitors to track the participants’ glucose levels during the study. They found that the participants’ average daily glucose levels were about 8% higher on the days that they took the caffeine pills than on the days when they took the placebos. Their post-meal glucose levels were also significantly higher on the days when they consumed caffeine.

These results were consistent with the findings of two previous small studies of caffeine’s effect on people with Type 2 diabetes. The new study was also small, but it was well-designed in that it was double-blind (the participants did not know if they were getting the caffeine pill or the placebo) and featured a crossover (all participants received the caffeine pill and the placebo at different times). However, its results are puzzling in light of some large observational studies, which have found that people who drink coffee appear to have a reduced risk of developing Type 2 diabetes. However, this effect may be due to the presence of compounds in coffee other than caffeine, such as antioxidants.

Some possible explanations for why caffeine may raise blood glucose levels are that it may interfere with the process that transports glucose from the blood into the body’s cells and that it may trigger the release of hormones that raise blood glucose levels.

The Duke researchers indicated that more studies are needed to fully understand caffeine’s effect on blood glucose. However, James Lane, Ph.D., the medical psychologist who led the Duke study, stated of people with Type 2 diabetes that “They may find that it’s easier for them to keep their glucose down if they avoid caffeine.” Writing on the subject in the January/February 2008 issue of Diabetes Self-Management magazine, though, Lynn Grieger, R.D., C.D.E, C.P.T., suggests that “Until more studies are conducted, it is probably best to limit coffee intake to moderate levels.” She also points out that a “cup” of coffee from a café or fast-food restaurant often contains more than 8 fluid ounces, so people looking to limit their caffeine intake should pay attention to portion sizes.

What have your experiences been with caffeine? Do you think it affects your blood glucose control? Bloggers Eric Lagergren and Andy Stuckey—both of whom have Type 1 diabetes, which wasn’t looked at in this study—have blogged about their suspicions that caffeine may have raised their blood glucose levels. (Check out Eric’s entry “In Praise of the Diabetes Contact List” and Andy’s entry “You’re Always On My Mind: Questions and Thoughts About Diabetes” for more.)

  • Philbur

    I totally missed this cause and effect until the old light bulb went off in my head. Yep, my levels do go higher on days I have caffeine. It happened today as a matter of fact. I dismissed it out of hand as a possible meter/meter strip fluctuation. Not much, but enough as to make me wonder. I only have caffeine on days I drive a lot. Diet Mountain Dew for me. I need to do a couple weeks of no caffeine and see if my levels are lower without it. Very cool stuff.

  • hararm13

    Went over to mixing 1/2 reg coffee and decaf in the am and decaf for later in the day…numbers in late afternoon are running about 120 instead of 160 4 out of 5 days!

  • tldell

    I agree with Philbur totally. I am a type II patient for several years now and a coffee drinker. After reading a similar report from another diabetes letter I decided to cut out my coffee for a couple of days. What do you think happened? My glucose remained mostly stable for the whole two days. I also was drinking decaffinated green tea. Does anyone want my left over coffee?

  • CalgaryDiabetic

    I was amazed how much my BS when up and for how long it stayed up when I drank a big cup of real coffee. Also you can forget about any sleep the following night which is a problem for most type II diabetics. My advice stick to decaf or omit entirely.

  • kmcewen

    What about caffeinated tea? I drink about 16-20 ounces a day. Also, which caffeinated teas cause lower blood sugar boosts?

  • Robert Baker

    I have found that drinking a cup of coffee in the morning after I take my blood count does not seem to change my blood sugar count significantly…..bob

  • Pati

    I’m one of the few it seems who has noticed lower blood sugars when I drink a cup of coffee. I never drink more than one a day, however, and no sugar (not even the “fake stuff”). I also drink herbal teas a lot, and plain water throughout each day. (The coffee does, however prevent sleep for a very long time —which it never did before diabetes “hit”.)

  • Nancy G.

    Thanks for the tip,going to try not having any caffeine for a few days.My sugar has been running high….Nancy G

  • mimi r

    i drink coffee every morning- no change

  • skip

    I really have a lot of doubt about any study which only has 10 subjects. At most it might suggest further, more rigorous study.

  • MIKI

    Never noticed any increase in BG after a coffee and I’m drinking a strong expresso.

  • Susan

    This morning I tested my fasting blood sugar and it was 102. After having a cup of caffeinated tea (no sugar), it went up to 129. Recently, after having a cup of coffee with breakfast, my blood sugar went up to 177! I’m definitely switching to decaf.

  • Ed S

    Since certain natural substances added to the diet have been shown to lower blood sugar (as the following ones), I would like to know if blood sugar is lowered by adding to coffee generous amounts of cinammon, nutmeg, or the sweetener stevia. Also, does adding lemon to tea lower blood sugar? In other words, would these additives negate the blood-raising effects of caffeine?

  • Sue T

    I rarely drink coffee anymore but have been drinking reg & green tea, both decaf. I have found that even “decaf” raises my blood sugar. The dietician said that even decaf has a small amount of caffeine.

  • john sugar

    Dear Sir
    I have type 2 diabetis I AM 74 Years old
    I use accu-chek device to monitor GI.
    Blood test evening 01.07.08 7. mmol
    Blood test morning after one mug instant coffee
    8.8 mmol
    Jhon Sugar

  • Leslie B.

    I do not have diabetes. However, I work at a rehab agency for people with vision impairment, and interact with people who have diabetes, both Type I and II. My understanding of diabetes is that blood glucose levels need to stay within an acceptable range, and that people who use oral meds. or insulin to control blood glucose need to be concerned both with readings that are too high, and also too low. Could people with diabetes (and the rest of us!) be using caffeine to raise blood glucose levels at times of the day when glucose levels are sinking unacceptably low? I am thinking that many people tend to drink caffeinated substances at mid-morning and mid-afternoon. Might this possibly be a healthier way to deal with mildly low blood glucose levels than a sugary snack?

  • Tara Dairman, Web Editor

    Leslie B.,

    Caffeine is not an approved treatment for hypoglycemia (low blood glucose), and trying to use it as such could be dangerous. As you can see just from reading the comments here, caffeine can have different effects on different people, and even if it does raise a person’s blood glucose level, it may take an unpredictable amount of time to do so.

    You may want to check out our article “Understanding Hypoglycemia,” which lays out the protocol for treating low blood glucose. Many different sources of fast-acting carbohydrate — such as milk, juice, or fruit — can be appropriate if a person wants to avoid candy or other “sugary snacks.”

  • troben46

    02/08/2009:
    I am a 62 year old white male Type 2 Diabetic. 12 years on oral meds. Now two weeks on Humalog (3-4 times daily before meals} and Lantus (10 units every evening). Still taking 2000 mg Metformin per day. I drink 8-10 cups coffee per day. My blood sugar definitely spikes. Example, this morning before breakfast my blood sugar tested 153 mg/dl. One hour later (still before breakfast)after a 24 ounce Dunkin’ Donuts Hazelnut coffee with milk my blood sugar tested at 188 mg/dl. This has been my continuing observation about the effect caffeine has on my blood sugar level. Time to quit.

  • Chris

    I just found this site this morning. I rarely drink diet soda. I actually love water (sometimes with lime or lemon). I have just recently been diagnosed with Type II. I am on 500 mg. of metformin and having lost 8 pounds and moderately exercising most days of the week, I have gotten my BS down to normal levels. I have been keeping a log of what I eat, when, levels, etc…..last night we were visiting friends and I decided to drink diet Coke and then to top it off, I had a 1/2 cup of Blue Mountain regular coffee from Jamaica (since we had all just visited there last month). I did have a small piece of birthday cake…2″x2″ without all the frosting. I was so proud of myself….
    This morning I took my BS on arising and to my dismay, it was 129!!!! I know that isn’t too out of range, but I have gone a whole month now with levels in the non-diabetic range.

    This morning I told my husband that I wondered if caffeine could have had anything to do with that reading (at first I thought the testing was in error)….came here to look it up and sure enough. I don’t even like diet pop….so, for me, I am thinking that three smalls cans of diet coke and a cup of Blue Mountain reg. could have been the dirty little culprit! What do you think?

  • Cordier Alain

    Hy

    I have just discovered this website.
    Awesome ! Thanks for all the news and comments. I’m 57, french and type 2 diabetic. I’m going to stop caffeinated beverages. A question: what do you think about chromium picolinate since your last article?

  • John

    I am brand new to all of this. Approx 2 months ago my doc told me I was T2 Diabetic (BS was why high 200+). Since that time I’ve dropped 20lbs and my avg BS is below 120 (a couple of spikes to 160 have kept it up). I don’t know if that is good or not? My doc is not very imformative and I do not know anyone else w/T2D to chat with? Any insights would be appreciated, thanks.

  • Chet

    I think that some people including testers may have forgotten to take several things into consideration. It is normal to have a plus or minus 20% in the absolute number you get from your glucose tester as compared to the lab test result. The lab test may be using a test that reads your whole blood while your blood glucose meter may be reading from a plasma sample. A lab test also can have inaccurate readings it depends when how soon the person ate prior to testing, how and how fast the blood was tested and when the equipment doing the test was calculated. Using pills instead of tea or coffee also confuses the issue. The different types of Tea and coffee processing and type is also a problem. I have come to the conclusion that the only real method is to see the effect of caffeine on a particular person is to have them eat, drink and exercise the exact same way for a period not less than one week and then repeating the process by having one cup of the substance (tea or coffee) you are testing. One also has to remember the test may also be valid only to the particular brand you are testing. On an individual level maybe trying one cup and averaging your numbers may also work but you need to be careful you have not changed your other habits and of course no additive to the coffee or tea as that would void the test.

  • Don

    I am newly diagnosed w/ type 2 so I have been checking my BS obssesively.I started to notice a sharp spike higher after a cup of coffee. Puzzled by this I googled and found this sight. For me anyway it seems true.

  • Chris

    I’m a regular coffee drinker and only yesterday started to monitor blood sugar. I had never heard about this problem until now. (Makes we wonder who’s trying to keep it quiet.) Yesterday I had a low-carb breakfast and 2 big cups of coffee and my blood glucose shot up from 118 before to 166 1 hr after (+48). Today I had the same breakfast but no coffee and it only moved from 112 before breakfast to 122 1 hr after (+10). I’ll experiment a little more but it seems like I’ll be switching to half-decaf or maybe full decaf.

  • Terry

    Since starting a candida diet about 4 weeks ago, I have had some amazingly low (meaning much better) glucose readings. Before, the readings were 120-200 during the day, now they are almost always below 70-100! But I noticed that for the last couple of mornings, when I had two cups of coffee and tea the evening prior, the reading was 165 and 190 the next morning. This was with my regular insulin shot (Lantus) the night prior. All cases of the evening meals were less than 50-60 carbs.

    I know from these and other past glucose episodes, caffeine definitely causes by blood glucose to go unacceptably high. I love the Candida diet and it does wonders for glucose control, but I am cutting out caffeine for good.

  • n. donaldson

    This study irritates me. Does caffeine cause blood glucose levels to rise or does it not? I am not giving up my coffee that I drink black at half strength for anybody or anyone or any disease. If the anti-oxidants are good for me then why are my levels so dang high? This makes absolutely no sense and is one of the reasons I cannot stand the medical and pharmaceutical professions. I am sick and tired of doing everything right and getting poor results. I believe it is the medication the doctors insist on prescribing screwing with my natural metabolism. I am only borderline on all counts, high blood pressure, high cholesterol, and high glucose, but the “professionals” have me on so many pills I am disgusted. They say they are looking out for my future health, but if my current health is okay, why oh why can’t anyone help me without medication? The pills cause more troubles than they cure!

  • Richard A. Manacle

    I always wondered why my numbers changed. I had a reading of 72, drank two 12 oz. cups of regular coffee and my reading after 1 1/2/ hours was 132. I didn’t consume anything but the coffee so I guess I’m going to Decaf.

  • steph w

    Well I am an extreme case study. I have been type 2 for several years now. 2 years ago my levels were spiking in the 300-400 range with no explanation. I wasnt eating anything that could cause this to happen. So I started monitoring my levels after certain foods and sure enought it was the morning and afternoon cups of coffee. I then switched to decaf and that was ok for about 6 months and the spikes started again. I quit caffeine altogether and have not had any high readings since. In fact when I exercise the go really low. The doctors I talked to all insist that the coffee was not the problem though.

  • Edward Marek

    I don’t have diabetes but at 58 I’ve been tracking my blood sugar as my father got type 2 diabetes around my age. I regularly take caffeine pills for alertness and have noted that the caffeine pills raise my blood sugar levels slightly (by around 10 to 15 points in my case). I’ve also noticed that it takes quite some time for the rise to be reversed.

  • Betty

    I am looking for Lemon Lime Cake for diabetics and is it true a doctor should be the one to cut your toenails?

  • Betty

    I meant Lemon Lime Cake recipe

  • Brandon

    I am a 27 yr old type I diabetic and have been for nearly 20 years now. I’ve had good to excellent control over it for years. Over the past year I have been using an omnipod insulin pump which has made controlling by bloodsugars so much easier, running an average A1C of 6.2 for nearly two years now. I just recently became a coffee drinker due to being around it with coworkers/classmates. I’ve been having issues with my bloodsugar raising in the mornings for the past few months, gradually increasing my basal rate by almost .75 units/hr and still waking up with a bloodsugar of 100 and three hours later it’s up to 200-250. If caffeine does cause the insuling to be less effective, this makes total sense, be continually raising my basal rate and still experiencing highs. I’m definately going to cut out the morning coffee and see if this makes a difference. I kept checking to see if my coffe had carbs that i wasn’t accounting for but could find nothing, diabetics will know how frustrating that can be to do everything right and still not have that control. It may not effect everyone this way, but it’s the only thing i’ve changed that could cause this. Hopefully this helps me regain my control, i’ll just have to go to bed earlier!

  • Darlene

    What about Type 1???? Why was this study just done on Type 2 patients? My sugars can go frm 80 to 380 within 2 hours of one cup of black coffee (no sugar or creamer). And the only info I can find on this is a study done only on Type 2’s. Frustrating.

  • Jean

    I am a newly diagnosed type 2 based upons A1C’s of 7.0 and 6.6.

    I could not understand why my blood glucose levels were so high at times and close to normal most of the time. The information from this site suggests that my problem could be the large amount of diet colas that I drink in the mid-afternoon and evening.

    Today, my fasting blood sugar was 104, and my bg 2 hours after breakfast was 110.

    I ate a low-carb, low calorie lunch and then drank 2 large cups of coffee, sipping the beverage slowly for a half hour before taking my bg two hours after eating. My bg had then spiked to 161!

    I will test after consuming other caffeine beverages.

    I am now wondering whether the impact upon caffeine is felt in non-diabetics as well. There is scant literature on this, but some evidence to suggest that even young, healthy individuals can have spikes due to caffeine.

    How wonderful to have this forum to sort out common issues.

  • Herb

    Last night before bed, my wife made me a cup of caffeinated tea by mistake that sat with the tea bag in the cup for an extended period of time. Not only could I not sleep for hours, but my fasting blood glucose which I have been monitoring for the last 5 days, and which dropped from 158 to 143, suddenly jumped to 153.

    By the same token, I did my nightly walk before taking my two hours after dinner blood test, and my reading dropped from 240 to 111!

    Either the counts are affected by caffeine and exercise before testing, or my meter is out of whack.

  • shell

    after reading all of the above am i right in thinking caffine affects blood glucose levels in type 1 too. this is quite worrying as i am a type 1 diabetic who ALWAYS drinks diet cola, thinking it was better for me as its sugar free. will exeriment now as i have been struggling lately to control my blood glucose levels x

  • alshawwa

    caffeine does effect the blood sugar but not in a direct way.

    if you read how caffeine effects the nerve system and the metabolism of your body , its actually gives your a body a unnecessary boost ” like a shock to your system” so its basically telling your body organs to work “over time work while your body doesn’t need it ” that’s why you feel awake when you drink any drink with caffeine ” alert mode”

    most of the organs are affected , especially the liver , the liver will produce more glucose to your body to give it the power its needs for that “shock” “wither you had food with the coffee or not” also it will effect the kidneys which a lot of people doesn’t know that it does save glucose in it for a while before throwing it out in case the body needed it

    caffeinated drinks have the highest impact
    decaffeinated drinks “does have caffeine but not a lot” does impact the glucose levels if you had more than 2 cups at a time.

    i switched to decaf drinks saw big differences in numbers , fasting or non fasting tests , post meals with coffee before and after.
    byt stopping the caffeine and the decaf drink is much better , try replacing it with water or milk “full fat with 12g of sugar” it will not effect the body the same way the caffeine does.

  • jim snell

    all said and done; unless the report says drinking black; I remain skeptical, period.

  • V S Mani

    Wonderful article more relevant to me after I visited my friend who has Type 1 for over 15 years and I have type 2 for 6 years. He remarked last week that whenever he drank filter coffee (only type he likes and so do I) the glucose value shot up by 2 points. I did not believe it as I felt that his BP may go up but not glucose.

    I tried it on myself by doing a fasting reading at 5.2 but after filter coffeee and 2 hours (no other food) it was 7.7 – worried me to bits. I do regular exercise – gym fanatic and swimming but unable to keep sugar level below 7 for over a year when during this period got addicted to filter coffee twice a day (measure is UK Tea cup). I am stopping this immediately and will inform my GP about my misbehaviour in diabetes control.

    Incidentally, I have taken Honey and found that values increased by 0.1 only after two hours – fasting 6.2 to 6.3 after a table spoon of honey without any other food. I take honey one teaspoon with each cup of coffee.

    I would like your comments, if convenient. Thanks

  • Mike

    I’ve been type 1 for 47 years and in pretty good shape considering my problem. I’m 62 now and retired. I’ve been wearing a pump for a little over 2 years now and I’m able to eat the way I like as long as I count carbs correctly which I’m pretty good at, so if caffeine raises your BS [blood sugar, that is] or at least have a tendency to raise it, I need to pay a little more attention to my morning “FIX”. Maybe after breakfast, not before!

  • sarah

    Just a comment, based on having a cup of tea before lunch today, non decaf…my number had soared up to 195. A usual prelunch for me is 90.

    As to all of the people who drink diet soda, just drink decaf diet soda instead. most diet lemon lime drinks are decaf and both pepsi and coke do decaf diet versions. When you eat out, it’s often easier to just drink water. Boring but safer on the sugar levels!

    My new endocrinologist was horrified by my 5.4 hga1c counts that my previous doctor loved, she has informed me that long term studies over the past decade or more have shown that keeping a glucose level of under 6 can have long term bad effects on other organs in your body, so she’s recommending keeping between 100-140 as much as possible. I’m finding this adjustment hard as i’ve spent 5 years trying to stay at 80…

    Good luck to everyone anyway :) Keep up the battle!

  • Aboona Joe

    Well, this morning I did a little experiment. Last night I had 2 peaches and this morning a third. Now, I’m usually much more discerning, knowing that, for me, any sweet will raise my count significantly, though not astronomically.

    So, this morning, before that 3rd peach, I was 147. After it, I was 153. After my morning java at SB — no cream, no sugar, a touch of cinnamon — i was 109!!!

    So, I don’t know: I’ll try again tomorrow. But, it sure does seem to me that that cupajava drove my # down!

    PS: I took or ate nothing else until lunch.

  • Lynda

    I have type two diabetes. I am beginning to think coffee may affect my glucose levels. My glucose reading in the evening about two hours after eating are on average about 108. My morning levels after fasting average 146. The only thing I can think of for this high number is coffee. Sometimes I drink a little coffee before I take my reading.

  • Mary

    I didn’t need a study to show me my blood sugar will raise with coffee…I’m not really a coffee drinker I average 1/2 a cup a day..and that little bit raises my blood sugar from 130 to 220 sure wish I new why… and it makes it harder to bring it back down the rest of the day…

  • Miriam

    I am a type 1 for 13 years.

    I have seen my blood sugar rise as high as 520 after drinking a coffee. and that is with taking a few units of insulin before because i know it can raise my sugars. any ideas what i can use instead to keep me focused and alert?

  • ada

    I am not diabetic. For decades I noticed that if I have coffee the cells of certain body parts swell a bit and act as if I have had too much carbs. I do not understand the biological basis for this reaction but Dr Atkins did mention to refrain from caffeinated beverages in his first book in the attempt to lower blood sugar. I believe one of his messages was that high levels of blood sugar was not good for us. It seems as if the coffee with no sugar acts if I were consuming too much sugar for my body type. Drinking caffeinated coffee produces the same reaction as if I had pasta. This is too bad because I enjoy coffee a lot. For me I see a direct relationship with coffee and my body’s reaction as if it were being feed high sugar content.

  • Billy

    Well, I’ve been T2 for 12 years. Just yesterday I started Lantus at night and take Metformin and glyburide. I woke up this morning with a reading of 6.6 on my meter. Ate 2 soft boiled eggs and 1 slice of dry whole grain bread. Drank 2 large black coffees. My after breakfast was 14.3 This shocked me. The only thing I had that I was not sure of was coffee. After reading this I think I will drink diabetic tea. I have a box and it has no caffeine. Great site. Am curious about what the non caffeine results will show. My past would see me drink 10 to 12 cups of coffee per day.

  • Mike

    I am a 50yo & a T2D for 15 years now & had BG readings all over the place until i started the following.

    In the morning when i wake at 7am, i eat 1 egg (sunny side up) & follow this with a 2 mile walk (shorter distances may work too, still trying to figure it out). Then nothing but herbal tea or water until lunch, when i have another egg. No snacks in the afternoon either. At 5 or 6pm, I go for another 2 mile walk (again, a shorter distance may work too, haven’t tried it yet). Dinner is usually a huge leafy salad (1/3 to 1/2 lb) with scallions, jalapenos, & a dressing with lots of olive oil & some vinegar (i like red wine, balsamic, & apple cider vinegar) followed by a little meat 4-6 oz & occasionally a 5 oz glass of red wine. Dessert is a hot 16oz drink made up of 2 heaping teaspoons of instant decaf coffee, 2 heaping teaspoons of unsweetened cocoa, 2 teaspoons of coconut oil, & 1 tablespoon of heavy whipping cream, & hot water. I’m never hungry at bedtime nor when i wake. I get hungry by lunchtime, but the egg takes care of that. And before the pre-dinner walk, i’m hungry, but the walk seems to take care of that.

    Since I’ve started this regimen, my fasting morning BG is usually 80-85. Eating nothing (no snacks) until lunch keeps my BG low (90-110) & the morning egg keeps my liver from putting out too much BG. The lunch egg does the same in the afternoon. 2 hours after dinner, BG is no more than 95-120. My BG keeps between 80-110 most days & occasionally peaks in the 120’s after dinner. I never get hypoglycemic. I have been taking 2 glipizides a day 5mg each, but may be cutting back when i see my doctor.

    Two things that i’ve noticed raise my BG are caffeine & cabbage, besides anything high carb, of course. One morning, I tried a few sips of my wife’s caffeinated instant coffee & my BG shot up from 79 to 152 in less than 1 hour! No more caffeine! Also, I loved shredded cabbage salad until i discovered that it also raised my BG a lot.

    Most of my calories come from fat, then protein, then leafy greens. I never eat sugar, bread, pasta, or anything with carbs. I stick to huge leafy green salads as a pre-biotic. Occasionally, i’ll have a few spoons of yogurt or a small chunk of cheese. I avoid processed meats & anything processed. Nothing in a box or can or even glass jar. No fast food ever. I rarely eat out, & when i do, it’s usually a salad with olive oil/vinegar, eggs, meat with no salt, low carb veggies.

    Bottom line: walk 2x per day every day, low carb, small low carb breakfast/lunch, lots of salad with real olive oil & a little meat for dinner. I spend at least 15 minutes in the midday sun every day for the vitamin D & take a vit D supplement.