Antioxidants such as Vitamins A, E, and beta carotene could be bad for health, says a meta-analysis. But read the criticism of other scientists on this biased reporting. Article updated April 4, 2011
Update 20 August 2009: Researchers at Harvard would be a laboratory study demonstrated that antioxidants promote cancer work. Great news for NOVA and the Times to broadly unpack. In a laboratory study of all places. The following study is also cited in the Volkskrant. Probably it becomes highlighted.
March 7, 2007: Source: Nutraingredients.com
The antioxidants A and E and beta carotene could reduce mortality of men by about 10%. Selenium could reduce mortality by 9%. This was clear from a meta-analysis of 68 randomized trials. However, there is a lot to note about this study. Here in English oi a readable critical analysis of how this study came about and what's wrong with it. In summary, there are these strange things to note and I quote from the article. But I start with an analysis of this study that physician-biologist Dr E. Valstar made at our request and to clarify anything to be desired:
JAMA study: a preliminary analysis by physician-biologist Dr E. Valstar
In JAMA from February 28 Bjelakovic et al have a number of randomized trials on as vitamin C, selenium, vitamin E, beta carotene and vitamin A analysis and hereby expressly looked to the death. However, this analysis was first a number of selection steps. Because they specifically wanted to look at mortality and not one item in each trial had been attacked on 405 of 815 studies, 69 trials were not randomized, 24 provided adequate data, and 4 were still 245 did not meet the criteria. This has been questionable: criteria for randomized trials in which mortality is viewed, but to exclude are highly subjective. All in all, remained on the opinion of the great trials of 68 writers.
Multivariate analysis (a precise method for correcting noisy and much more objective than univariate analysis) resulted in: no difference, except that selenium supplementation was found to reduce mortality significantly. The question is whether this also was found thrown out if the 245 studies were included.
An objection to this kind of meta-analysis (also indicated by Stampfer of Harvard) is that many studies are too different: if you're using a small x in a lower mortality study regarding a specific disease is taking a big total population adds another way in which x about a very different ailment does nothing, the addition leads to the disappearance of the previous significance, such as numerically with a chi-square test (2) easy to prove. That selenium is nevertheless positive roll out the 'overall' analysis is therefore remarkable.
The rejection of the 245 is ridiculous because of the large number of studies and especially by the large number of people the standard errors anyway greatly diminished (see 2: The error means should the root of the number of participants in the corresponding total group are shared, if the total control group of 100 persons to 490,000 then the standard error in the number of smoking years, eg 70 days, 1 day). Selection based on selective / subjective criteria undermines the statistical reliability.
Bjelakovic et al also did their subgroup of 68 studies, a further sub-sub-group analysis. It appeared the result of discussions among the authors, with already familiar with a nota bene completed research often cited to indicate in which sub-study found a subgroup. This further selection is also ridiculous because self Bjelakovic et al on page 845 with two different statistical tests in these 68 studies found no heterogeneity (ie it calls itself further against the benefits subsubgroepanalyse, although I do believe that this kind of testing never able to establish a maximum heterogeneity). It was precisely in the subsubgroepanalyse usually uni but no multivariate analysis was done. In their view, most studies carried out (something which the necessary doubt) was then vitamin A and E have an adverse effect on mortality found, but in other subsubgroepen just the opposite. Factor is that by introducing more subgroups (or rather subsubgroepen) and the chance of more variables toevalssignificanties also further increase, I could not find this corrected.
It had the largest group by limiting it only to evaluate the multivariate analysis. That Bjelakovic et al pursued after their disbelief is also reflected in the fact that they are in no way a relationship between the duration that a substance or substances have been taken to trace and mortality. No results with selenium is what is most to be trivialized and subsubgroepanalyses opgekuifd be selective. This studytherefore ripe for the recycle bin. Why not targeted meta-analysis with a parameter in all trials with the same problem? PSK is already done (3): 15% fewer deaths from colon cancer stage B / C. I know there is one that will promote: melatonin in metastatic cancer; Bjelakovic lets look at research as something positive comes off very consistent in randomized studies, that he will not do because I think he does not believe in these funds.
References
1) Bjelakovic G et al, JAMA 297, 842-57, 2007.
2) Wijvekate ML Inferential Statistics, 1972, Het Spectrum, Antwerpen.
3) Sakamoto J et al, Cancer Immunol Immunother 55: 404-11, 2006.
below:
Below is from an article that was sent to me via interent.
Bjelakovic and staff of the University of Nis in Serbia, and Ospedale V. Cervello in Palermo, starting with 1201 references distributed over 815 trials / studies. 747 trials / studies utigelstoen for different reasons today: Yahoo in 405 trials, there were no deaths among the participants (what a shame it that it not be included if your starting point is to see if intake is bad for health and you as a student leader the media approached the one-liner: antioxidants increase mortality by 10%), 69 studies were not randomized, 245 trials did not meet the criteria for admission (there is not here why not) and 4 trials are ongoing.
"Most of the trials that were included in the analysis were examined antioxidants in high doses. Higher than a balanced diet and generally exceeded the permitted or recommended daily allowance.
In addition, most members who took part in the studies already examined a common (severe) disease such as heart disease and cancer. Only two studies !!!!! were performed in people who were models for an average person. When looked at the whole and compared to compare to other groups, no significant difference in risk of dying. However, investigators have searched for very specific individual antioxidants and draw their conclusions.
Read on below what else the comments but this seems clearly a prearranged plan to antioxidants in a bad light.
Study links antioxidant supplements to Increased mortality
By Stephen Daniell
28/02/2007 - A meta-analysis of 68 randomized trials with antioxidant supplements HAS Reported That vitamins A and E, and beta-carotene May increasefontsize mortality risk by up to 16 per cent, but vitamin C did not have an effect on mortality and the antioxidant mineral selenium was associated with a nine per cent Decrease in all-cause mortality.
The pooled analysis, published in the Journal of the American Medical Association, could-have significant negative effects on the sale of dietary antioxidant supplements, much like the effects of another meta-analysis, published in 2005, That Reported a 10 per cent or Increased Risk mortality for people takingcare 400 International Units per day of vitamin E.
The EARLIER meta-analysis, published in the Annals of Internal Medicine (142 (1) :37-46), Has Been highly criticised and discredited as flawed, but sales or vitamin E, Particularly in the U.S., declined / significantly in the wake of ITS publication.
The new pooled analysis HAS Already drawn criticism from Both inside and outside the dietary supplements industry Applied Concerning the methodology, and the Conclusions Drawn.
The Most prevalent criticism of the study Has Come From The diverse nature of the studies pooled together, described by one industry expert as Comparing "apples and oranges".
More About, Meir Stampfer, a professor of nutrition and epidemiology at the Harvard School of Public Health who was not connected to the meta-analysis, the Associated Press Told That Were the studies reviewed too differential to be bootable to pool together themself.
"This study does not advance our understanding, and Could Easily lead to misinterpretation of the data," Stampfer Told the AP.
A wealth of epidemiological evidence HAS linked dietary antioxidant intake to Reduced Risk of a wide range of diseases, Such as cancer and cardiovascular disease, but When Such antioxidant Have Been Extracted and purified, or synthesised and put key in supplements, the antioxidant, According To randomized clinical trials (RCTs), do not always produce positive results The Same.
"Our Findings contradict the Findings of observational studies, antioxidant Claiming That Improve Health. Considering That 10 per cent to 20 per cent of the adult population (80-160 million people) in North America and Europe May consume the assessed supplements, the public healthconséquences May Be Substantial, "wrote Goran Bjelakovic, from Copenhagen University Hospital's Center for Clinical Intervention Research, and lead author of the new meta-analysis.
Bjelakovic and collaborators from the University of Nis in Serbia, and Ospedale V. Cervello in Palermo, followed the Cochrane Collaboration method for meta-analysis and started with 1201 references-describing 815 trials. Seven hundred and forty seven trials for Several Reasons Were excluded, include no mortality in the study groups (405 trials), the studies Were not randomized trials (69 trials), They did not fulfil inclusion criteria (245 trials), or the studies are ongoing (four). The Remaining 68 randomized trials Used beta-carotene doses ranging from 1.2 to 50 milligrams, vitamin A from 1333 to 200 000 International Units (RDI 5000 IU, Upper Safe Limit 10,000 IU), vitamin C from 60 to 2000 mg (RDI 60 mg UL 2000 mg), vitamin E from 10 to 5000 IU (RDI 30 IU, UL 900 IU), selenium and from 20 to 200 micrograms (RDI 65 micrograms, UL 450 micrograms). "Most trials Investigated the effects of supplements at higher doses Administered Than Those comm only found in a balanced diet, and some of the trials Used doses well above the recommended daily allowances and even above the tolerable upper intake level," said the reviewers. Many of the studies included only subjects classified as Already Suffering from Certain diseases. Indeed, only two of the studies classified as "low bias" were Carried out in the 'general population'. When Their tasks in entirety, antioxidants Were found to have no significant effect on mortality. This result did not hold however When The reviewers Looked at the nutrients singly and removed studies That They enforcement classed as a high bias in Favour of the antioxidant. In the 47 classified as low-bias trials (180,938 participants), overall antioxidant supplements Were associated with a five per cent Increased Risk of Mortality. When The reviewers classified as vitamin A intake "Given singly or in combination with Other antioxidant supplements after exclusion of high-bias risk and selenium trials," use of the vitamin was associated with a 16 per cent Increased Risk of Mortality. Beta carotene and vitamin E was associated with seven and four per cent Increased risk of mortality, respectively, whereas there was no Increased mortality risk associated with vitamin C and selenium use was associated with a nine per cent Decreased Risk of Mortality. "There are Several Possible explanations for the negative effect of antioxidant supplements on mortality. Although oxidative stress Has A hypothesized role in the pathogenesis of many chronic diseases, it May Be the conséquence of Pathological conditions. By Eliminating free radicals from our organism, we are interfering with some essential defensive mechanisms. "Antioxidant supplements are synthetic and not Subjected to the Same Rigorous Other toxicity studies as pharmaceutical agents. Better understanding of mechanisms and actions of antioxidants in Relation to a potential disease is Needed, "concluded the researchers. The study Has Been slammed by the US-based Council for Responsible Nutrition, who said the researchers' Misuse [d] meta-analysis methods to create generalized Conclusions That May inappropriately confuse and alarm Consumers Who can benefit from supplementation tion with antioxidants. "More About, Andrew Shao, Ph.D., CRN's vice president, scientific and regulatory affairs said thats the combined studies Were far too diverse and differentiate into terms of dosage, duration, study population and nutrients Tested thats the results of the analysis were "compromised". Additionally, Dr.. That must Shao noted of the trials included in the meta-analysis Tested for secondary prevention, looking at how a nutrient works in diseased Population, INSTEAD of primary prevention studies in healthy Populations. "Combining secondary prevention and primary prevention trials and then making Conclusions for the Entire population is an unsound scientific approach," said Shao. "Additionally, many of the trials, Limitations, Including the expectation That a simple antioxidant vitamin could-be expected to overturn serious illness, Such as cancer or heart disease. These trials Likely statistically skewed the results. "Daniel Producer, vice president of scientific affairs for Natural Products Association (NPA), another US-based trade association, supported this view." Despite the authors' contention, this analysis is Assessing mortality or at risk-and diseased population - versus a healthy population - in prevention trials. The risk of mortality must be attributed to the 'appropriate population studied, Those with An existing health condition, Which in this case it isn't. INSTEAD, Those Findings are generalized to a healthy general population, Which is wrong on many levels, "said Producer." But what's musts trou bling Is That People Who Are Taking vitamins Safely and beneficially Might stopWhich May Actually pit at Greater Risk Their Health. "Manufacturer Also Stated That if a true mortality risk was apparent leg in any clinical studies or thesis Using antioxidants, Would Have Been halted the study, but none Were." Nearly 160 million people in North America and Europe use the attributed supplements. If antioxidant Were a significant public health risk, as the authors speculate, It Would Clearly have become apparent by now, "he said." Obviously This is not the case: They refer to the negative effect of bone HAS not seen in the population. " Source: Journal of the American Medical Association February 28 2007, Volume 297, Pages 842-857 "Mortality in Randomized Trials of Antioxidant Supplements for Primary and Secondary Prevention: Systematic Review and Meta-Analysis" Authors: G. Bjelakovic D. Nikolova; L. Lotte Gluud, RG Simonetti, C. Gluud
