*This is a guest post from Jonathan Carp, MD,

There seems to be some confusion regarding the safety of coffee.   The confusion is because epidemiological studies have been inconclusive.  Coffee itself contains numerous compounds and has more than one effect on the human body so teasing out what is causing what has been difficult.  The main arguments against studies that do show a positive correlation between intake and myocardial infarction (heart attack)1 has been recall bias (inaccuracy of people's memory of actual coffee consumption) and other factors like smoking that could be associated with coffee drinking.

Your liver is responsible for handling all of the caffeine you throw at it.   It is done through an enzyme called cytochrome p45 1A2 henceforth known by its abbreviation CYP1A2.    To make this as simple as possible, based on genetics, you are either a "rapid" metabolizer or a "slow" metabolizer.

Cornelis et al has shown that an increase in nonfatal myocardial infarction is related only to people with who are "slow" metabolizers.  Some interesting notes on this important study. 2

1. Young "slow" metabolizers  are most at risk. As the study states "the risk associated with drinking 4 cups/d or more compared with less than 1 cup/d increased from 2-fold for individuals younger than 59 years to more than 4-fold for those younger than 50 years" This was also observed in another study 3 that showed greater risk among women 45-60, than above 60.

2. Rapid metabolizers showed no risk and in fact, there was a protective effect if they drank more than 1 cup of coffee as compared to less than 1 coffee per day.

3. It is still unclear what the actual reasons why slow metabolizers have a higher rate of nonfatal myocardial infarction - mechanism suggested has to do with adenosine receptors which affect the ability of your vessels to open and vasodilate.

4. The risk for heart attack was highest with 4 cups per day in the slow metabolizers.

5. The study accounted for smoking, waist to hip ratio, income, physical activity, history of diabetes, history of hypertension, and intakes of alcohol, and total energy, and energy adjusted intakes of saturated fat, polyunsaturated fat, trans fat, folate, and sucrose. While one can't completely control for all factors that could influence the results - this is impressive.

Another study showed a similar risk for hypertension (high blood pressure).4

My recommendation is to avoid caffeine if you are a slow metabolizer while others have recommended to limit it to one cup per day or 100mg per day. if you are fast metabolizer, enjoy your coffee, but I still wouldn't go above 4 cups of coffee per day or 400mg per day.  If you are 70+ year old, don't worry about it.

The "body hacking" community has embraced caffeine in a big way and I think that knowledge of these studies should be made more available. You can get yourself tested for this enzyme by a few limited labs (along with other tests) - (see below).

People LOVE coffee, if you do, and have no desire to give it up - its best to know if you are a slow or fast metabolizer. I'd say that if you are one of those people that gets super jittery quickly with caffeine and it stays with you, you are probably a slow metabolizer so I would be cautious but that is not the most scientific test.  Of course, if you get the test you will know.

If you "need" coffee in the morning - why not start figuring out why?  It means your health is out of balance in some way.   It is simply not normal for anyone functioning optimally to require a stimulant to "get going."  We all make this deal with ourselves, we will use something to get through the stresses of life, how we choose those things is important to our overall health.    Like it or not, we make withdrawals from our bank account of health when we choose caffeine or other agents over other methods, like exercise, walking, or the vast amount of other non taxing methods to increase our store of energy.

If you love coffee for the taste and the cultural aspects of this drink - go for it just do it with the knowledge you have just learned.

If you want to know if you are fast or slow metabolizer, I can get that test to you at cost.   I am offering nutrigenomics consultations and until I reach 100 formal consultations I will get you the test and a formal 30 minute video review with me of the results at cost.  So far, I have just tested my family and some friends.   This test will test your genetics for caffeine as well as a whole host of 45 other factors including data on glycemic index, folate, sodium intake, special nutrient needs for Vit A, B12, C, D, E, Iron, Calcium, protein, fat, and food intolerances such as lactose and gluten.  It also tells you about how many carbs are ideal for you based on a gene that encodes amylase.  If you are interested

  1.  Sign up as a patient free of charge at my Online Portal
  2.  Do not set up an appointment just message me in the portal about nutrigenomics and I will send you details, (it's a saliva test) - the cost is $350 and that is the cost the lab charges - I will do a 30 minute result by result review for free via video to go over the results so you understand them correctly.
  3. When I reach 100 patients - I will start charging for this review to compensate me for my time but until then you will just be charged the actual cost of the test.  I am doing this at cost without me making any money because I want to build an expertise in this exciting field and a starting core of online patients that are using this information to benefit their health.   50 hours of my time seems worth it to me.

You may be thinking why you haven't heard of this before, well - while the number of studies and their quality are impressive at this early stage, the testing for these has not been easily available.  When some of these seminal studies were done, those tests had to be sent to a special lab.   A few months ago at a national dietician show in Boston,  I met a lab that is allowing physician's like myself who have an interest to run these tests on my patients.   So far, as I mentioned I have only run a handful of people.

This is the future, I can assure you,  but it won't be widely adopted for some time because large scale data on impacts of this knowledge affecting health outcomes will take some time to be gathered5 and when they do, it will be one data point at a time, that will be added to an insurance company's approved labs.    But that doesn't mean that you as an individual can't take some control of your health situation yourself.   Quite frankly, most physicians and dieticians aren't yet educated enough or interested enough to help you with this.   Any physician, who has spent time with the studies as I have, however, realizes how eye opening this data is for a person and how informed you become so that the educated choices you make about your diet are especially for you and aren't based on the latest recommendations by the guru of the year!

Keep it in mind and if you wish to get the tests done follow the instructions above.


1.Kawachi I, Colditz GA, Stone CB. Does coffee drinking increase risk of coronary heart disease? results from a meta-analysis. Br Heart J. 1994;72:269-275
2. Cornelis et al. Coffee, CYP1A2 genotype, and risk of myocardial infarction. JAMA. 2006;295:1135
3. Palmer JR, Rosenberg L, Rao RS, Shapiro S. Coffee consumption and myocardial infarction in women.  Am J Epidemiol. 1995;141:724-731
4. Palatini P et al. CYP1A2 genotype modifies the association between coffee intake and the risk of hypertension. J Hypertens. 2009 Aug;27(8):1594-601
5. Nielsen DE1, El-Sohemy A. A randomized trial of genetic information for personalized nutrition. Genes Nutr. 2012 Oct;7(4):559-66. Epub 2012 Mar 11.

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