Friday, September 21, 2012

Cranberry juice may help lower BP but…


All you need to do is drink two 8 ounce glasses of cranberry juice per day for 8 weeks and your blood pressure will be statistically significantly lower. So states a randomized, blinded placebo-controlled trial presented at this year’s American Heart Association's High Blood Pressure Research.

According to the MedPage Today report, mean diastolic blood pressure fell by a whopping 3 mm Hg from baseline at the end of the study period. The difference was significant at the level of p = 0.049. Subjects given placebo showed no change in their average BP.

Unfortunately, as appealing as this may sound, it’s another situation where statistical significance and clinical significance part ways. I have blogged about this before.

What are the problems with cranberry juice study?

The subjects were people of normal body mass index (average BMI, 28) who did not have hypertension.

The mean fall in diastolic blood pressure was from 72 mm Hg to 69 mm Hg, both of which are in the normal range. A 3 mm Hg difference in diastolic blood pressure, even if it had occurred in a patient with hypertension, is not a clinically important difference.

Systolic BP also fell by 3 mm Hg but the difference was not statistically significant, p = 0.12. A quote from the article states, “The trend didn't meet traditional criteria for statistical significance, but the 89% odds of a systolic blood pressure reduction with the cranberry juice was still pretty good, [a study author] suggested.” Sorry, not only is that baloney, a 3 mm Hg difference in systolic BP is also not clinically important.

A study from the Mayo Clinic found that when blood pressure is measured every 10 minutes throughout the day in healthy adults, both systolic and diastolic BPs varied as much as 8 to 10 mm Hg whether the subject was active or not. This indicates that a 3 mm Hg difference is very likely to have occurred by chance.

Finally, the study was funded by Ocean Spray Cranberries and one of its employees was a co-author.

You can drink cranberry juice if you like its taste, but don't throw away the BP pills.

6 comments:

Mike Bronson said...

This is not only a perfect deconstruct of this study but it's also an illustration of the old saying "figures lies and liars figure." A statement can seem so logical until others analyze it.

Prov 18:17 The first to plead his case seems right, Until another comes and examines him.

Skeptical Scalpel said...

Thanks for commenting. Unfortunately, this type of "study" is all too common in medicine.

cynthia said...

I'm getting rather sick and tired of being bombarded with nutritional health claims like this one -- coming out of the medical-industrial complex, no doubt. Such claims are either frivolous, biased, or both. I don't know who's funding this research, but if the taxpayers are ( thanks in part to medical Keynesianism, I'm afraid), then I say stop the funding of it! Let it fall off the fiscal cliff, along with all of the outrageous pork and subsidies going to Big HealthCare!

Don't get me wrong, I'm all in favor of funding research that leads to better understanding of diseases and better drugs to treat diseases. But funding research that results in promoting cranberry juice, red wine or black coffee as a 'wonder drug' or 'magic pill 'is a total waste of time and money.

Bottom line: all research studies such as these and others should be classified as pseudoscience, and thus banned from scientific research, especially research that's being funded by the taxpayers. Now if private corporations want to waste their money on research, that's based on pseudoscience, they should be free to do so, but they shouldn't get tax breaks for it.

Where is Richard Feynman when we need him. We need him here to beat the drums that pseudoscience is nothing more than a Cargo Cult.

Skeptical Scalpel said...

Cynthia, thanks for commenting. I agree with you. Also, this one was funded by the people who make cranberry juice. It's no surprise that the result was spun as showing a benefit for drinking the juice.

Elinor Phillips said...

People has its ways of promoting their products and one is investing in a research study that claims for its good health benefit, like cranberry juice as remedy and a bladder cancer alternative treatment. I just don't know if they were able to prove it.

Pregnancy And High Blood Pressure said...

It is important to remember that pregnancy and high blood pressure affects the fetus as well as the mother. Occurs in around 5% of all pregnancies and covers a wide range of conditions.

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