Habitual consumption of coffee and high blood pressure
A recent analysis of some trials investigating intake of coffee and high blood pressure has shown that high levels of intake were not associated with an increased risk of hypertension.
The study, published in the American Journal of Clinical Nutrition, by Dr Zhenzhen Zhang, from Michigan State University, and other colleagues, reviewed six long-term studies that examined the association of long-term habitual consumption of coffee and high blood pressure risk.
Six studies which investigated in total 172,567 participants were examined. The authors compared lowest consumption (1 cup or less per day, with one cup being 237ml) with moderate intake (3–5 cups per day) and the highest category (over 5 cups per day). A dose-response meta-analysis showed an inverse 'J-shaped' curve. This means that the hypertension risk increased up to 3 cups then decreased with higher intakes.
The authors concluded that habitual coffee consumption of greater than 3 cups per day was not associated with an increased risk of hypertension compared with <1 cup/d; however, a slightly elevated risk appeared to be associated with light-to-moderate consumption of 1 to 3 cups daily.
I was really hoping for something less equivocal from this meta-analysis. (We reviewed another more favourable study on coffee here).
For those who may be confused by the terms I should explain a little. A meta analysis is really desk-based research. Someone takes the time and trouble to look for clinical studies on a topic that meet certain criteria and whose results can be combined to give a bigger picture. If they all seem to point in the same direction then it can give a powerful statistical argument.In this meta analysis the results of six trials were examined and this gave a massive group of 172,567 people for whom there is good data on coffee consumption and blood pressure over a long period of time.
Unfortunately, what the results tell us about coffee and high blood pressure, is a case of the coffee cup being either half full or half empty depending upon how you wish to look at it.
A worried hypertensive person would probably note that moderate consumption does confer a slightly increased risk of hypertension and therefore take this as advice to reduce intake to under one cup a day. A coffee lover like me who has greatly reduced his intake already could be tempted to take the counterintuitive (though mouthwatering) step of consuming at least five cups per day. Confusing!
The study also raises a number of questions, the obvious one being why the strange relationship of coffee and high blood pressure, with highest intake appearing to be as safe as lowest intake. Does coffee contain something beneficial to blood pressure that only works at high doses?
In conclusion then, what is the take away message for those of us with high blood pressure? Well, although the blood pressure effects identified so far are small, my personal opinion as a coffee lover is that if my BP was not under control I would reduce my intake to a small cup per day to see if I could knock off a couple more points from my readings. As it is under control, however, I will carry on as I do taking two to three cups per day with one being decaffeinated. I certainly wont be going back up to five cups per day.
You may be interested in this article on coffee and high blood pressure
Source: Habitual coffee consumption and risk of hypertension: a systematic review and meta-analysis of prospective observational studies Am J Clin Nutr June 2011 ajcn.004044; First published online March 30, 2011.
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