dras knowledge

Thursday, August 16, 2007

New Study: Vit A&E Don't Prevent Heart Disease

http://www.newstarget.com/021976.html
Following yesterday's announcement of a new study showing the phenomenal benefits of antioxidants for preventing heart disease in women, the mainstream media rallied behind a blatantly false distortion of the study designed to convince the public that vitamins E and C are somehow useless. The popular press, which maintains an incestuous relationship with the pharmaceutical industry, once again demonstrates it is little more than a mouthpiece for the pro-pharma propaganda machine. There is no scrutiny of the study's findings, no critical thinking and absolutely no independent journalism being conducted by the mainstream media on this particular topic. It's as if these media outlets just can't wait to be spoon-fed the latest propaganda from drug company collaborators and then parrot it out to the public as fact.
The distortion in question concerns the assessment of women who participated in a nine year trial measuring the effects of vitamins E and C. According to the results published in the Archives of Internal Medicine, women who took these vitamins on a regular basis experienced a remarkable and statistically significant reduction in stroke risk (31 percent) and heart attack risk (22 percent). Not all the women in the study, of course, actually took the vitamins on a regular basis, and when you count the results of those women who never took the vitamins, the study shows no statistically significant benefits for vitamins E and C. In other words, the vitamins didn't work on those who didn't take them. (Is this surprising to anyone?)


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Firstly, this article does no present good evidence for a "incestuous relationship" existing between the press and pharmaceutical industry. If this person paid so close attention to the published study, they'd see some study sponsors are big names in in the industry, who, it's assumed, could benefit nicely by a positive outcome. Also, the press can't be expected to be too critical in parroting the printed results. The study report has a 3-sentence summary that includes, "Overall, we found no benefit on the primary combined end point for any of the antioxidant agents tested, alone or in combination."

This whole newstarget rant lost it's credibility in the conspiracy theory-laden first paragraph. Nevertheless, I considered their second criticism of the reporting of study outcomes that are based on intent-to-treat analysis. In this study, researchers wanted to know whether giving different anti oxidants to a large specific population made an obvious difference. It didn't. Intent-to-treat analysis are valid because they reflect what would probably happen in the population were it real versus a study. Does the study conclude an individual probably won't benefit by taking vitamins E and C? No, because that's not what the study was trying to determine. This is a large epidemiological study, where it will be inherently difficult to find valid statistical significances beyond the clearly obvious. The good data from such study are the almost sweeping generalizations about specific populations. Variability can clutter up the validity of conclusions that
are based on a drilled down analysis. So, the study results also cannot conclude that an individual taking E and C are probably a good thing (like newstarget infers) either.

The study authors admit that subject compliance is a real shortcoming in analysis of the data. And they do consider the impacts of using intent-to-treat analysis: "To examine the impact of lack of compliance, a post hoc sensitivity analysis censored women if and when they stopped taking at least two thirds of their study medication, reported taking outside supplements containing study agents, or were missing compliance information. Statistical analysis were conducted using SAS version 9 (SAS Institute, Cary, North Carolina), using 2-sided tests with a significance level of P < .05."

dras

P.S.
I thought Prof. Dallal's critical notes about "intention-to-treat" linked from wikipedia are excellent and very applicable in considering the data from this study: http://www.tufts.edu/~gdallal/itt.htm

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