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Is Coffee Bad for You?

Is Coffee Bad for You?

Many of us enjoy a good cup of coffee in the morning, or two, or three…  For others, there’s frequent stops at Starbucks, Dunkin Donuts, or Tim Hortons throughout the day.

If you drink more than one cup of coffee per day, one question that you may be asking yourself, is drinking coffee bad for your health?

Research on the safety of coffee?

To answer that question in part, a recent study published in the Journal of Clinical Nutrition (Kerstin et al, 2010), studied the impact of drinking coffee on cholesterol levels, risk factors for type 2 diabetes, oxidative stress, and subclinical inflammation.

In this particular study, people who were classified as habitual coffee drinkers refrained from drinking coffee for one month.  For the second month, they consumed 4 cups of coffee per day and a whopping 8 cups per day for the third month.

Health effects of coffee consumption:

“Significant changes were also observed for serum concentrations of interleukin-18, 8-isoprostane, and adiponectin (medians: –8%, -16%, and 6%, respectively; consumption of 8 compared with 0 cups coffee/d).”

  • Higher concentrations of Interleukin-18 (IL-18) has been previously identified as a risk factor for type 2 diabetes.
    • Coffee consumption lowered serum concentrations of IL-18.
  • 8-isoprostane is a marker of inflammation, it decreased by 16% with consumption of 8 cups of coffee/day.
  • Low levels of adiponectin is associated with insulin resistance and type 2 diabetes.
    • Adiponectin levels increased by 6% which could theoretically reduce the risk of developing type II diabetes.

“Serum concentrations of total cholesterol, HDL cholesterol, and apolipoprotein A-I increased significantly by 12%, 7%, and 4%, respectively, whereas the ratios of LDL to HDL cholesterol and of apolipoprotein B to apolipoprotein A-I decreased significantly by 8% and 9%, respectively (8 compared with 0 cups coffee/d).”

Does coffee consumption increase your cholesterol?

Their results are more difficult to interpret in the context of previous research.  However, this particular study used filtered coffee as opposed to unfiltered coffee.  HDL or ‘good cholesterol’ levels increased with consumption of coffee in this study.  The study authors suggest that at the very least, coffee consumption did not have an adverse effect on serum cholesterol.

Does coffee consumption increase your risk of diabetes?

“No changes were seen for markers of glucose metabolism in an oral-glucose-tolerance test.”

The study authors cite a number of previous studies which suggests that coffee consumption and type II diabetes is inversely related.  In that sense, drinking coffee may have a protective effect against developing type II diabetes.  This particular study may not have been long enough to observe an effect of coffee consumption on glucose metabolism.

Bottom line:  Is coffee bad for your health?

First, the results of this study are limited in context to the effects of drinking coffee on serum cholesterol, oxidative stress, and glucose metabolism.

The results of this study suggest that even drinking 8 cups of coffee per day did not have an adverse effect on serum cholesterol levels. As well, coffee consumption did not have an adverse effect on glucose metabolism.


  1. Kerstin Kempf, Christian Herder, Iris Erlund, Hubert Kolb, Stephan Martin, Maren Carstensen, Wolfgang Koenig, Jouko Sundvall, Siamak Bidel, Suvi Kuha, and Jaakko Tuomilehto.  Effects of coffee consumption on subclinical inflammation and other risk factors for type 2 diabetes: a clinical trial.  Am J Clin Nutr. 2010 Apr;91(4):950-7. Epub 2010 Feb 24.


  • Josh Kohlbach

    Good news for me then :) I'd love to see a study on the impact of programming skills and coffee consumption!

    • Jarret Morrow, M.D.

      Josh, I'll follow up with some further articles about other aspects of coffee/caffeine. I would imagine that there's probably a ton of caffeine consumption behind most software programs.

  • Leny

    Too much coffee can't be good. The problem is that people usually shift their coffee-drinking habit to some other addictive behavior once they start with trying to quit regular drinking of coffee. Some turn to excessive eating, some to other stimulating drinks...I guess people are really creatures of habit, in this way or another!

    • Jarret Morrow, M.D.

      Leny, that could be a possibility. When people try to cut down or quit drinking coffee, they can go through caffeine withdrawal symptoms including headaches...

  • Laurie Ross

    This is encouraging news for me. Starbucks is a daily habit, and I always drink a cup or two of coffee before the gym. I'd love to see some information about the affect of caffeine on cortisol, if there is one.

    • Jarret Morrow, M.D.

      Laurie, caffeine consumption typically results in an increase in cortisol levels particularly during times of stress. Some research suggests that in young, healthy subjects who drink coffee on a regular basis, this effect is reduced but not eliminated.

  • Craig

    It's good to know that drinking coffee doesn't raise your cholesterol levels. I drink around 8 cups per day myself, so I guess that I'm in the clear. I'll check out the next article to see what other health effects result from drinking coffee, well, maybe after I get back from Starbucks. I'm going to order a Venti Caramel Macchiado. :)

    • Jarret Morrow, M.D.

      Craig, I wouldn't recommend drinking that much coffee especially on a long-term basis. Caffeine itself has a fairly long half-life, so if you drink that much coffee regularly, it will likely interfere with the quality of your sleep at the very least.

  • KC Craichy

    Unless the coffee is organic, it is one of the highest pesticide-laden crops in the world.

    • Jarret Morrow, M.D.

      KC, I haven't read or researched the quantity of pesticides in these crops, do you have any pertinent info on this? thanks.

    • virginia

      I agree on the need for organic... yall should check out this blog on organic coffee that boosts immune system.

  • AlexandraFunFit

    This is a very interesting study. As a researcher/editor, I appreciate seeing the actual research quotes, plus the conclusions. A surprising result, too, I must say.

  • Greg

    Interesting research about coffee consumption. It sounds like coffee may actually reduce the risk of developing type 2 diabetes. thnx.

  • Dean

    I think it's important for people to keep in mind that this study probably didn't include coffee beverages that are loaded with Calories like specialty coffees from Starbucks, Dunkin Donuts, etc. I think that I read somewhere that a Caramel Macchiato has as many calories as a Big Mac from McDonalds.

    • Jarret Morrow, M.D.

      Dean, I think that I read the same article in Men's Health a few years ago. I do seem to remember that Starbucks specialty coffees have similar calories as a Big Mac, but I would have to double check to confirm it.

  • SmarTasz

    Here's some insight. Coffee: Tastes great, wakes me up, helps me function more efficiently, elevates overall mood, and helps me poo. (sorry ladies) On the other hand, Anything you do in excess is bad for you, especially caffeine! And so, the bads would be high blood pressure and anxiety, as well as discomfort in the stomach (felt and unfelt). There are tons I don't know about coffee, but I know it has antioxidants and a great effect on Office Jobs. Which I should get back to.. take it easy. Especially you, 8-cups-a-day-guy.

  • caroline

    iv switched over to green tea instead of coffee way better for you and helps in weight loss, coffee left me with anxiety and sleepless nights. coffee in moderation should be fine, but if your an athlete like my self you should just cut the crap out of your diet. Since iv cut out diet pops and artificial sweeteners, creams and coffees and increased excercise and water intake ( green tea) i have lost 10 pound in 2 months. Take it or leave it!

    • Valle

      Personally, I agree that green tea(especially decaf) is much better than the amount of caffeine in coffee. Caffeine has been shown to lower resistance to infections by lowering the immune systems response. I was surprised to see that it makes no glucose difference because it stimulates pancreatic production of insulin, although it is a stimulant. Nice articles and site. I enjoyed the reading.

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