Posted on 02/28/2007 2:45:16 AM PST by XR7
Vitamin supplements taken by millions of people every day for their health could be increasing their risk of death a new Danish-led study suggests.
The study is published in the Journal of the American Medical Association.
The international research team reviewed the published evidence on beta carotene, vitamin A, vitamin E, Vitamin C and selenium. The team was led by Dr Goran Bjelakovic, from Copenhagen University Hospital, Denmark.
These dietary supplements are marketed as antioxidants and people take them in the hope they will improve health and guard against diseases like cancer and heart disease by eliminating the free radicals that cause "oxidative stress" and damage and kill off cells.
Antioxidants are also marketed as anti-aging products because they are thought to slow down the aging process.
Some studies have suggested that antioxidants are beneficial to health, while others, mostly larger clinical trials, have concluded they have no effect on health and say in some cases that taking too many of them can be harmful.
In this study, Dr Bjelakovic and colleagues did a meta-analysis on research published before October 2005.
Meta-analysis is a way of sifting through published studies against a quality standard that looks at a number of reliability criteria such as potential for bias. Then the ones that pass the standard are taken through a statistical process to find out if they are saying something consistently reliable. There can be several levels of "sifting", each producing a more reliable and robust set of evidence.
In this case the researchers followed a method established by the Cochrane Collaboration, a group of 6,000 health care specialists who review biomedical trials and other research projects.
They started with 815 clinical trials of which 68 passed the first level of quality standard. At this level the results were inconclusive. The supplements were found to have no effect on death risk one way or the other.
They then went back and eliminated 21 of the trials, leaving only the "low-bias" ones. This was the next level of quality standard.
At this level of meta-analysis the results were different.
When looked at separately they found that Vitamin A increased death risk by 16 per cent, beta carotene by 7 per cent and Vitamin E by 4 per cent. The results for Vitamin C were not so clear, but by looking at the best quality trials there was a suggestion that it increased death risk by 6 per cent, either on its own or in combination with other supplements.
The figures from the best quality trials on selenium however showed that it might reduce death risk by 10 per cent, either on its own or in combination with other supplements, but this was not found to be statistically significant.
The overall conclusion of the study was that on balance, the best quality research shows that beta carotene, vitamin A and vitamin E may increase mortality risk, but vitamin C and selenium need further study.
A spokesperson for the supplements industry said the research was "flawed" because it included studies conducted on people who were already very sick.
The researchers say there are several potential reasons for these results. One is that the free radicals that are thought to cause the oxidative stress are the byproduct rather than the cause of disease. Another is that they may play an important role in the immune system and eliminating them could be counterproductive.
The researchers pointed out that the studies they examined only used synthetic supplements, and therefore their observations and conclusions do not apply to natural antioxidants such as those found in fruit and vegetables.
They added however that this study is important for public health reasons because between 10 and 20 per cent of people in Europe and North America take dietary supplements.
Nutritionists say that instead of taking supplements the best way to protect your health is to eat a balanced diet and to get all the vitamins you need from your food.
"Mortality in Randomized Trials of Antioxidant Supplements for Primary and Secondary Prevention; Systematic Review and Meta-analysis." Goran Bjelakovic, Dimitrinka Nikolova, Lise Lotte Gluud, Rosa G. Simonetti, and Christian Gluud. JAMA 2007;297:842-857. Vol. 297 No. 8, February 28, 2007
Thanks so much!
I have been in the pharma business for a long time (and worked in pharma nutrition for ten years also) and I take one Centrum Silver per week, an extra few grams of folic acid every week but 3 tablets/day of vitamin D (GNC's "Vitamin D 700") as cholecalciferol. FWIW.
Fair enough. I'm not signing on to the full-on tinfoil hat brigade on this. I was just a little suspicious of this study.
You're absolutely correct about MSM/Chrondroitin/Glucosamine for arthritis. I forgot about that. It works.
3mg of C a day?
That doesn't even cover the USDA/FDA minimums, which is what, a minuscule 68mg, just enough to keep scurvy at bay.
Are you sure you don't mean 3 grams?
As I'm a smoker, I take around 5~6g a day, and I can feel the difference. The doc also put my dad on CoQ-10 and suggested I do the same. So I'm taking about 200mg a day.
I've also read that among mammals, there are only three that do not produce their own C and require it from diet/supplements. Humans, Gorillas, Hamsters, and there might be one other, can't recall.
And IIRC, blood serum levels of other mammals that do produce their own C extrapolated to human weight/mass, would result in serum levels in the 10's of grams.
Realized that I wrote 3 mg. inst. of (3000 mg. or) 3 g., but figured I'd wait until someone else noticed it ;-)
LOL! And I was only thinking that meta-analysis might just be compounding exponentially the inadequacies of the earlier studies! You're right though -- it's the wave of the future!
Regards, Ivan
"Meta-analysis might just be compounding exponentially the inadequacies of the earlier studies!"
Yes, I had not thought of this, but you are right. That's 2 things conceptually wrong with Meta-analysis. Meta-analysis as described so far is not a valid technique.
I once took a course in advanced statistics and experimental design. I believe our instructor would have laughed at any of us who had proposed anything like this for a real science study.
Physicians generally pooh-pooh the value of vitamins, but this is because you can get vitamins into your body without the aid of physicians. If the only way it could be done was for a team of eight surgeons to implant a special $263,000 trapdoor in your head, physicians would say vitamins were the best thing since luxury German automobiles.
I always trust Dave Barry! ;-)
. . . or, as James Taranto of Best of the Web Today put it: To 105%?
Growing old isn't so bad when you consider the alternative.
I'd like some evidence that the people who did this study ever took an undergraduate statistics course.
The figures from the best quality trials on selenium however showed that it might reduce death risk by 10 per cent, either on its own or in combination with other supplements, but this was not found to be statistically significant.
Are they saying that a 4% increase in death stats is significant but a 10% decrease in death is insignificant? Makes you wonder what their bias was...
Hi Coleus....that's interesting.
Someone told me to take hawthorn for my blood pressure. I tried it, but perhaps I wasn't taking the correct dosage, so I resorted to a medication my physician gave me. I was living dangerously with hypertension for too long.
Bjelakovic et al. published similar articles in The Lancet (2004), and in Alimentary Pharmacology & Therapeutics (2006). The flaw in all three studies is the same. They used multiple linear regression, a technique that averages in people who took moderate doses of vitamins along with people who took highly toxic doses of vitamins.
The average dosage for vitamins A and E in their new study were at levels already known to be toxic; the maximum dosages were about 20 times the recommended levels. Of course there was some mortality - just as a study of people who took 1 to 100 tablets for a headache, and pretended the dose-response was linear, would show that "aspirin increases mortality".
People frequently cite the many numbers and measures of statistical significance in Bjelakovic's studies as evidence of the validity of their results. Statistical significance means nothing if the test being performed is nonsensical.
Dr. Bjelakovic has not responded to my request to see his data in order to run a multiple nonlinear regression test on it. It is fairly certain, from prior studies, that such a test would show that vitamins A and E have beneficial effects up to dosage levels of about 5,000 and 300 IU/day, respectively.
Appropriate dosage levels depend on age, sex, and weight, as well as personal genetics and medical condition - so be careful out there.
More details on how to correctly interpret the study data are on my livejournal page, shagbark.livejournal.com .
- Dr. Phil Goetz
Thanks.
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