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Auf dieser Seite sollen Presseberichte, die, begründet oder unbegründet, Warnungen zum (übermäßigen) Konsum von Vitaminen und anderen Mikronährstoffen mitteilen, kommentiert und ggf. richtig gestellt werden.

 Zunächst Berichte und Kommentare zu Vitamin E

und Vitamin C 


Thema (A): Vitamin E


Abschnitt I


Pressemitteilung Spiegel:

(Gegendarstellung hierzu im Abschnnitt II)

 

Forscher warnen vor Vitamin-E-Kapseln

Viele Menschen schlucken die Vitamin-E-Präparate zur Vorbeugung von Herzkrankheiten. Vor allem bei höherer Dosierung können die Kapseln jedoch genau diese auslösen, stellten US-Forscher in einer Studie fest.


Wer täglich eine Kapsel mit 400 oder sogar 800 Internationalen Einheiten (IE) Vitamin E zu sich nimmt, erhöht das Risiko eines frühzeitigen Todes um zehn Prozent. Dies ist das erschreckende Ergebnis von der Johns Hopkins University in Baltimore durchgeführten Studie. Ein Milligramm der Vitamin-E-Verbindung Tocopherol entspricht je nach seiner genauen Zusammensetzung zwischen 1,0 und 1,5 IE.

Die Wissenschaftler hatten insgesamt 19 verschiedene klinische Studien aus den Jahren 1993 bis 2004 ausgewertet. Insgesamt flossen in die Metastudie Daten von 136.000 Patienten ein, die Vitamin-E-Kapseln einnahmen.

Viele dieser Patienten greifen zu dem Vitamin-Präparat, um Herzkrankheiten vorzubeugen. Doch die Wirkung tritt nicht ein, ganz im Gegenteil. Teilnehmer, die höhere Dosen von Vitamin E zu sich nähmen, trügen auch ein höheres Todesrisiko, sagte der Leiter der Studie, Edgar Miller, auf einer Tagung der American Heart Association in New Orleans.

Originalkurzfassung hierzu in Englisch

11/10/2004

High doses of vitamin E supplements do more harm than good

NEW ORLEANS, Nov. 10 – Daily vitamin E doses of 400 international units (IU) or more can increase the risk of death and should be avoided, researchers reported at the American Heart Association’s Scientific Sessions 2004.

The study is being simultaneously released on the Web site of the Annals of Internal Medicine.

In animal and observational studies, vitamin E supplementation was shown to prevent cardiovascular disease and cancer.  However, other studies suggested that high doses could be harmful.

To determine if there is a “dose response,” researchers examined different doses of vitamin E supplements and risk of death from any cause.  They studied death rates in published clinical trials comparing vitamin E supplementation to placebo and included findings from 14 studies, from 1993 to 2004.  Doses ranged from 15 to 2000 IU/day, and average intake was about 400 IU a day.

“Increasing doses of vitamin E were linked to an increase in death,” said lead author Edgar R. Miller, M.D., Ph.D., associate professor of medicine at Johns Hopkins University in Baltimore, Md.

According to the analysis, there is no increased risk of death with a dose of 200 IU per day or less, and there may even be some benefit.  However, an increased risk was found at amounts above 200 IU per day and significant risk of death was found starting at 400 IU a day.  Those who take greater than 400 IU of vitamin E a day are about 10 percent more likely to die than those who do not, researchers said.

“Many people who take vitamin E supplements take between 400 and 800 IU in a single capsule,” said Miller.

The confusion for many, said Miller, is that some doctors have recommended vitamin E supplementation based on studies suggesting that it is beneficial for specific illnesses.  One study in people with a history of prior heart attack showed that vitamin E use correlated with a lower risk of having a second event.  In another trial, patients with end-stage kidney disease seemed to benefit.  However, in both of these studies (in fact, in seven of the eight high-dose vitamin E trials in this analysis) the patients on vitamin E supplementation were more likely to die than those in the placebo group.

“Typically, we get about 6-10 IU per day of vitamin E in our diets.   Vegetable oils, nuts and green leafy vegetables are the main dietary sources of vitamin E.   Supplementation can increase intake by 100-fold,” said Miller.             

Researchers said the current U.S. dietary guidelines do not recommend vitamin E supplementation, but indicate that the upper tolerable limit of intake is 1000 IU per day.

There is room for more research, however, on the effects of 200 IU or less per day of vitamin E and how low doses taken in combination with other vitamins might positively affect death rates, he said.

“The big questions that need to be answered are: What is the dose?   And how low a dose – in what combination – would be most useful?” Miller said. 

Co authors are Roberto Pastor-Barriuso Ph.D.; Darshan Dalal M.D., M.P.H.; Rudolph A. Riemersma Ph.D.; Lawrence J. Appel M.D., M.P.H. and Eliseo Guallar M.D., Dr.P.H.

Statements and conclusions of study authors that are published in the American Heart Association scientific journals are solely those of the study authors and do not necessarily reflect association policy or position.  The American Heart Association makes no representation or warranty as to their accuracy or reliability.
 

Abschnitt II

 Gegendarstellungen

 (wir werden uns bemühen, diese Gegendarstellungen in absehbarer Zeit ins Deutsche zu übersetzen, benötigen dafür aber etwas Zeit)

 1. Gegendarstellung: 

 Linus Pauling Instutute for Orthomoleculare Medicine

 
Vitamin E Supplementation and All-Cause Mortality

A recent meta-analysis that combined the results of 19 clinical trials of vitamin E supplementation for various diseases, including heart disease, end-stage renal failure and Alzheimer's disease, reported that adults who took supplements of 400 IU/day or more were 6% more likely to die from any cause than those who did not take vitamin E supplements (52). However, further breakdown of the risk by vitamin E dose and adjustment for other vitamin and mineral supplements revealed that the increased risk of death was statistically significant only at a dose of 2,000 IU/day, which is higher than the UL for adults. Furthermore, three other meta-analyses that combined the results of randomized controlled trials designed to evaluate the efficacy of vitamin E supplementation for the prevention or treatment of cardiovascular disease found no evidence that vitamin E supplementation up to 800 IU/day significantly increased or decreased cardiovascular disease mortality or all-cause mortality (53-55). At present, there is no convincing evidence that vitamin E supplementation up to 800 IU/day increases the risk of death from cardiovascular disease or other causes.
Tolerable Upper Intake Level (UL) for Alpha-Tocopherol
Age Group  mg/day (IU/day d-alpha-tocopherol)
Infants 0-12 months  Not Possible to Establish*
Children 1-3 years 200 mg (300 IU)
Children 4-8 years 300 mg (450 IU)
Children 9-13 years 600 mg (900 IU)
Adolescents 14-18 years 800 mg (1,200 IU)
Adults 19 and older 1,000 mg (1,500 IU)

*Source of intake should be from foods or formula only.

Drug interactions

Individuals on anticoagulant therapy (blood thinners) or individuals who are vitamin K deficient should not take alpha-tocopherol supplements without close medical supervision because of the increased risk of hemorrhage (3). A number of medications may decrease the absorption of vitamin E, including cholestyramine, colestipol, isoniazid, mineral oil, orlistat, sucralfate, and the fat substitute, olestra. Anticonvulsant drugs such as phenobarbitol, phenytoin, or carbamazepine may decrease plasma levels of vitamin E (3, 50).

Antioxidants and HMG-CoA reductase inhibitors (statins)

A 3-year randomized controlled trial in 160 patients with documented coronary heart disease (CHD) and low HDL levels found that a combination of simvastatin (Zocor) and niacin increased HDL2 levels, inhibited the progression of coronary artery stenosis (narrowing), and decreased the frequency of cardiovascular events, such as myocardial infarction and stroke (56). Surprisingly, when an antioxidant combination (1000 mg vitamin C, 800 IU alpha-tocopherol, 100 mcg of selenium, and 25 mg beta-carotene daily) was taken with the simvastatin-niacin combination, the protective effects were diminished. However, in a much larger randomized controlled trial of simvastatin and an antioxidant combination (600 mg vitamin E, 250 mg vitamin C, and 20 mg beta-carotene daily) in more than 20,000 men and women with coronary artery disease or diabetes, the antioxidant combination did not adversely affect the cardioprotective effects of simvastatin therapy over a 5-year period (57). These contradictory findings indicate that further research is needed on potential interactions between antioxidant supplementation and cholesterol-lowering agents, such as HMG-CoA reductase inhibitors (statins).

  
2. Gegendarstellung: 

Council of responsable nutrition (www.crnusa.org)

 
Vitamin E meta-analysis in Annals of Internal Medicine:

What’s wrong with this picture?

 
What is a meta-analysis?

 A meta-analysis is not a clinical trial. It is a statistical technique for combining the results of many
existing studies in order to clarify possible effects. When studies are done with a few hundred or
even a few thousand people, it is often difficult to determine whether differences between the
treatment group and the placebo group are “real” or just accidents due to chance. Combining studies
provides more people for analysis and thus increases statistical power. While a meta-analysis is an
important scientific tool, it also has limitations.

 
What is all-cause mortality?

Studies are generally designed to look at some particular outcome, like whether vitamin E reduced the risk of having a heart attack. However, in studies involving sick people and lasting for several years, there will be other outcomes, such as death. A certain number of people in longterm studies are going to die, and all-cause mortality is the number of people who died from any cause—whether or not the cause has anything to do with the purpose of the study. All-cause mortality includes people who died of heart disease or infectious disease or cancer or getting hit by a bus. The number of people who die in the treatment group and in the control group will rarely be exactly equal. Statistical analysis tells us whether differences in total mortality between the treatment group and the control group are significant or just the result of chance.
 

What did this study find, overall?

This study analyzed 19 clinical t rials in which vitam in E was given, involving a total of almost 140,000 people. Eighteen of the 19 trials individually found no statistically significant increase in tot al mortality in the vitamin E group. Even when all of the 19 trials were combined, there was no significant increase in tot al mortality. The study authors say, “T he average death risk across trials in t he control groups was 1022 per 10,000 persons. Overall, vitamin E supplementation did not affect all-cause mortality.”


What did the study find, relating to high and low doses of vitamin E?

When the trials were divided according to the dose of vitamin E, the researchers found that low doses of vitamin E slightly decreased total mortality while high doses of vitamin E (400 IU or more) slightly increased total mortality. The researchers said this was a statistically significant effect, but others have criticized whether it has practical meaning. Most of the high-dose studies were done in people who already had various diseases and the authors say that these findings may not be generalizable to healthy adults. However, they go on to generalize, saying that people should avoid high-dose vitamin E and indeed high doses of any vitamin—a conclusion much more sweeping than is justified by their analysis.

 
Were there other findings?

The researchers also did a dose-response analysis of the clinical trials, which found a statistically significant (but very small) increase in mortality only when the vitamin E dose was greater than 900 IU. This is contrary to the finding in their main meta-analysis that doses over 400 IU might confer increased risk.

 More facts on the vitamin E meta-analysis

 What were the 19 studies used in this meta-analysis?

T he studies chosen f or the m et a-analysis all lasted more than one year and reported at least 10 deaths from all causes. Studies in which no deaths occurred were not included in the analysis. The studies were originally published in t he decade from 1993 to 2004. Some of the studies involved over 20,000 people, and some involved only a few hundred people. Doses used in the studies ranged from 16.5 I U t o 2000 IU and were given for periods from one to 8 year s. In some studies the vitamin E was given as part of a multivitamin or some other mixture of nutrient s, and in some studies vitamin E was given as a single nutrient . The studies were conducted in various parts of the world—Europe, Asia, t he Middle East, Australia, Canada, and the U.S. Vitamin E was given in these studies for many different purposes, including reducing t he risk of heart disease, cancer, and macular degeneration and delaying the progression of cataracts, kidney disease, Alzheimer ’s disease and Parkinson’s disease. 
 

Some of the studies found a benefit o f vitamin E for these purposes.

Do any of the studies show a benefit from vitamin E?

 Yes. Many of the 19 clinical studies used in this meta-analysis actually showed a health benefit from vitamin E. For example, one study in England showed that vitamin E at levels of 400 and 800 IU reduced the risk of heart attack by 75% in men who already had symptoms of heart disease. A study in patients with kidney failure found a reduced risk of heart attacks and of death from heart disease in people who were given 800 IU of vitamin E. Another of the studies found that vitamin E (400 IU) in combination with some other nutrients reduced the risk of age-related macular degeneration, the leading cause of blindness in elderly people. And one study showed that a very high dose of vitamin E (2000 IU) delayed the progression of Alzheimer’s disease.
 

Do epidemiologic studies show a benefit from vitamin E?

Yes. Numerous epidemiologic studies have shown a benefit from vitamin E. In an epidemiologic study, researchers simply observe whether people who use certain products or adopt certain habits on their own have more or less disease than people who do not. A Harvard study of more than 80,000 nurses found a 41% reduction in the risk of heart disease in nurses who had used vitamin E supplements for at least 2 years. A Harvard study of almost 40,000 male health professionals (mostly dentists) found that men who took vitamin E supplements for more than 2 years had a 37% reduced risk of heart disease. A study conducted by the National Institute of Aging in 11,000 elderly people found that those who used supplements of vitamins C and E had a 53 percent reduction in mortality from heart disease and a 42 percent reduction in all-cause mortality, compared to non-users.

 
Are more studies being done using high-dose vitamin E?

Yes. A number of new clinical trials are now under way, and researchers are attempting to reassure the people enrolled in these trials that vitamin E is safe and that the research should continue. They include the Women’s Health Study involving over 40,000 female health professionals, the Physicians’ Health Study involving thousands of U.S. doctors, and the Women’s Antioxidant Cardiovascular Disease Study. Also, the National Cancer Institute is sponsoring the Selenium and Vitamin E Chemoprevention Trial (SELECT) to evaluate the effects of these two nutrients in protecting against prostate cancer in more than 30,000 men.
 

More facts on the vitamin E meta-analysis

Was it reasonable to select 400 IU as the cut off between low-dose and high-dose vitamin E?

No. Four hundred IU was an arbitrary number. It is not evident how the researchers chose to define 400 IU and not some other value as the “high-dose” mark, except that it is the most commonly marketed dose in the U.S. Two important studies including the GISSI trial in Italy used 330 IU of vitamin E—not much lower than 400 IU. Including those in the high-dose group would have been reasonable, and the positive effects of the GISSI trial would have offset some of the studies showing a trend toward increased mortality. Below that dose, there is only one study at 200 IU, also showing a slightly beneficial effect on total mortality. The truly “low-dose” studies are the five that used only 60 IU or less of vitamin E. In short, it appears that 400 IU rather than 200 or 300 IU may have been arbitrarily selected as the high-dose cutoff in order to bolster a finding of risk.
 

How much vitamin E is safe?

The Institute of Medicine, a scientific advisory body, has concluded that vitamin E is safe for chronic use in the general population at levels up to 1000 mg (1000 IU synthetic vitamin E, 1500 IU natural vitamin E). The Recommended Dietary Allowance for vitamin E is 15 mg (15-22.5 IU, depending on the chemical form), and only a small fraction of the population gets this much from diet alone. Most multivitamins contain 15 to 60 IU of vitamin E.
 

What should people think about this meta-analysis?

This meta-analysis does not change what is known about vitamin E safety. It used no new research but instead combined 19 studies in order to create statistical significance for a finding of a slight increase in all-cause mortality in studies that used 400 IU or more of vitamin E, but overall the studies showed no such increase and a dose-response analysis showed a significant increase only at levels above 900 IU. The authors have exaggerated the practical significance of their findings to attract attention and scare the public. As a result, numerous participants in ongoing clinical trials on high-dose vitamin E sponsored by the National Cancer Institute have been needlessly frightened, and the future of the studies may be endangered. Consumers who are already using vitamin E should continue to use it with confidence, and people who are not currently using at least a multivitamin containing vitamin E should consider doing so, since the overwhelming majority of the population fails to get the recommended amount of vitamin E from diet alone.

 rev11/22/04

 

Thema (B): Vitamin C

 Abschnitt I

Pressemitteilung Spiegel:
 
(Gegendarstellung/Kommentar hierzu im Abschnnitt II !)


Auch Vitamin-C-Pillen steigern Herztod-Gefahr

Von Jochen Kubitschek

Erst vor wenigen Tagen haben Mediziner vor einer Herz-Kreislauf-Gefahr durch Vitamin-E-Pillen gewarnt. Nun gerät auch synthetisches Vitamin C ins Zwielicht: Eine Langzeitstudie besagt, dass die Pillen das Risiko einer lebensbedrohlichen Herzkrankheit zumindest für Diabetiker drastisch erhöhen können.

Erst vor wenigen Tagen hatten US-Wissenschaftler gewarnt, dass in höheren Dosen eingenommenes Vitamin E das Risiko für Herzinfarkte nicht wie angenommen senkt, sondern sogar erhöht. Nun gerät auch das bei vielen Gesundheitsaposteln besonders beliebte Vitamin C ins Visier der Zweifler - zumindest, wenn es als synthetisches Vitamin C in Tabletten daherkommt.

Ein Forscherteam um David R. Jacobs von der University of Minnesota konnte jetzt nachweisen, dass hoch dosiertes Vitamin C in Pillenform die Gefahr von Herz-Kreislauf-Erkrankungen zum Teil drastisch erhöhen kann. Ausgerechnet in der wichtigsten Risikogruppe für einen vorzeitigen Herztod - ältere Frauen, die unter Diabetes leiden - können die Pillen das Herzinfarktrisiko nahezu verdoppeln, schreiben die Wissenschaftler im Fachblatt "American Journal of Clinical Nutrition".

Schon vor Jahren war den Ärzten aufgefallen, dass die Vitamin-C-Konzentration im Blut vieler Zuckerkranker ungewöhnlich niedrig ist. Dieser für Diabetiker typische Mangel stand als eine der Ursachen für die Häufung einer frühzeitigen Arterienverkalkung und der daraus resultierenden Herzinfarkte in Verdacht.

Trügerische Sicherheit

Vitamin C wird von vielen Menschen zur Vorbeugung gegen Arterienverkalkung eingenommen. Auch viele Zuckerkranke hoffen, dass die frei verkäuflichen Vitaminpillen bei ihnen das Herztodrisiko senken. Denn seit der zweimalige Nobelpreisträger Linus Pauling hohe Dosen von Vitamin C als Vorbeugung gegen viele Krankheiten empfohlen hat, ist die Ascorbinsäure zu einer Art Volksnahrungsmittel avanciert.

Schaden könne Vitamin C in keinem Fall, lautete bisher die landläufige Meinung. Doch die Untersuchung von Jacobs und seinen Kollegen, durchgeführt über einen Zeitraum von 15 Jahren, scheint nun zu beweisen: Das Gegenteil ist der Fall - zumindest was Zuckerkranke angeht, von denen es in Deutschland zwischen vier und fünf Millionen gibt.

281 der 1923 Diabetikerinnen, die an der Studie teilgenommen hatten, starben während der 15-jährigen Dauer der Untersuchung einen Herztod. Nachdem die Wissenschaftler alle anderen bekannten Risikofaktoren für Herz-Kreislauf-Erkrankungen statistisch ausgeschlossen hatten, erlebten sie eine Überraschung: Das höchste Risiko für bedrohliche Erkrankungen der Herzkranzgefässe hatten ausgerechnet jene Diabetikerinnen, die täglich mehr als 300 Milligramm Vitamin C in Pillenform eingenommen hatten. Das war nicht einmal um eine besonders hohe Dosierung: Linus Pauling etwa hatte pro Tag 1000 bis 1800 Milligramm empfohlen. Bei Nicht-Diabetikern hatte die Vitamin-C-Einnahme dagegen keinen Einfluss auf die Wahrscheinlichkeit von Herzerkrankungen, schreiben die Forscher.

Zweifel bestanden seit Jahren

Die Zweifel am Sinn der Pillentherapie sind nicht neu. Bereits 2002 wurden im Fachblatt "The Lancet" die Ergebnisse der "Heart Protection Study" veröffentlicht, an der über 20.000 Briten teilgenommen hatten. Nach fünf Jahren Studiendauer kamen die Forscher zu dem ernüchternden Schluss, dass die in hoher Dosierung in Pillenform zugeführten antioxydativen Vitamine E, C und Beta-Carotin zwar keine sofort erkennbaren Schäden angerichtet hatten. Aber auch das Herzinfarkt- oder Krebsrisiko hatten sie, anders als erhofft, nicht gesenkt.

Warum Vitamin C aber das Herzinfarktrisiko sogar deutlich steigern kann, ist auch für Jacobs und seinen Kollegen ein Rätsel. Bei der Ursachenforschung tippen sie auf die schon länger bekannte Tatsache, dass Ascorbinsäure nicht nur antioxydativ, sondern unter bestimmten Bedingungen auch oxydationsfördernd wirkt.

Diese widersprüchliche Eigenschaft werde offenbar immer dann neutralisiert, wenn Vitamin C als natürlicher Bestandteil von Obst und Gemüse in den Körper aufgenommen wird. Die Förderung der für die Blutgefäße schädlichen Oxydation von Bestandteilen des Nahrungsfetts - besonders des "bösen" LDL-Cholesterins - komme anscheinend dann zur Entfaltung, wenn das Vitamin C in Form synthetisch hergestellter Vitaminpillen in den Stoffwechsel gelangt.

Die von Experten als äußerst wichtig bewertete Untersuchung legt abermals nahe, dass die industriell hergestellten Vitaminpillen keinesfalls die in frischem Obst und Gemüse enthaltenen natürlichen Vitamine vollwertig ersetzen können. Auch die Annahme, dass wasserlösliche und daher mit dem Urin auszuscheidende Vitamine selbst in hoher Dosierung keinen Schaden anrichten können, dürfte der Vergangenheit angehören.

Originalkurzfassung hierzu in Englisch:

Supplemental Vitamin C Could Increase Heart Disease Risk in Diabetic Persons

Because plasma vitamin C concentrations are often subnormal in diabetic persons, Jacobs and colleagues at the University of Minnesota evaluated the relation of vitamin C intake to cardiovascular disease risk in a prospective 15-year study of 1923 borderline overweight, postmenopausal, diabetic women. Publishing in this month’s American Journal of Clinical Nutrition, the authors made the unexpected discovery that the risk of coronary artery disease was greatest in the quintile of patients who consumed the highest amount of daily vitamin C, even though this group had the lowest intake of saturated fat from their diet. Further analysis revealed that this finding was related specifically to the amount of supplemental nondietary vitamin C, with twice the risk of coronary disease among those taking more than 300 mg per day. The authors speculate that this adverse effect of supplemental vitamin C relates to the unique properties of this vitamin as both an antioxidant and a prooxidant and that the biological effect of the supplement is less likely to be modified by dietary factors.

Lee D-H, Folsom AR, Harnack L, Halliwell B, Jacobs DR Jr. Does supplemental vitamin C increase cardiovascular disease risk in women with diabetes? Am J Clin Nutr 2004;80:1194-200.[Abstract] [PDF]

 

Abschnnitt II

Gegendarstellungen

(wir werden uns bemühen, diese Gegendarstellungen in absehbarer Zeit ins Deutsche zu übersetzen, benötigen dafür aber etwas Zeit)
 

Eine erste kurze Gegendarstellung des Linus Pauling Instutute for Orthomolecuolare Medicine auf unsere Anfrage:

Dear Dr. Matschurat,

I am sorry to delay so long in answering your question about the recently published study on vitamin C supplement use and cardiovascular disease mortality in diabetic women. I wanted Dr. Balz Frei, the director of the Linus Pauling Institute, to read and comment on my discussion of this study before publishing it on our web site. Clearly, more research is needed to determine whether vitamin C supplement use is beneficial or harmful to individuals with diabetes. I hope that these puzzling findings will stimulate other investigators to examine their data on supplement use and cardiovascular disease risk in diabetic individuals. Here is the information that I plan to publish in our Micronutrient Information Center on vitamin C: http://lpi.oregonstate.edu/infocenter/vitamins/vitaminC/index.html#disease_treatment

Cardiovascular diseases (heart disease and stroke) are the leading cause of death in individuals with diabetes. Evidence that diabetes is a condition of increased oxidative stress led to the hypothesis that higher intakes of antioxidant nutrients could help decrease cardiovascular disease risk in diabetic individuals. In support of this hypothesis, a 16-year study of 85,000 women, 2% of whom were diabetic, found that vitamin C supplement use (400 mg/day or more) was associated with significant reductions in the risk of fatal and nonfatal coronary heart disease in the entire cohort as well as those with diabetes (1). In contrast, a 15-year study of postmenopausal women found that diabetic women who reported taking at least 300 mg/day of vitamin C from supplements when the study began were at significantly higher risk of death from coronary heart disease and stroke than those who did not take vitamin C supplements (2). Vitamin C supplement use was not associated with a significant increase in cardiovascular disease mortality in the cohort as a whole. Although a number of observational studies have found that higher dietary intakes of vitamin C are associated with lower cardiovascular disease risk, randomized controlled trials have not found antioxidant supplementation that included vitamin C to reduce the risk of cardiovascular disease in diabetic or other high-risk individuals (3, 4)

 It is possible that genetic differences may influence the effect of vitamin C supplementation on cardiovascular disease. When the results of one randomized controlled trial were reanalyzed based on haptoglobin genotype, antioxidant therapy (1000 mg/d vitamin C + 800 IU/d vitamin E) was associated with improvement of coronary atherosclerosis in diabetic women with two copies of the haptoglobin 1 gene but worsening of coronary atherosclerosis in those with two copies of the haptoglobin 2 gene (5). The significance of these findings is not entirely clear, but they suggest that there may be a subpopulation of people with diabetes who will benefit from antioxidant therapy while others may not benefit or could actually be harmed. Since randomized controlled trials have not found that supplementation with vitamin C is beneficial in preventing or treating heart disease in individuals with diabetes, individuals with diabetes should avoid consuming more than 250 mg/day from vitamin C supplements until more research is available. Since vitamin C intake from foods was not associated with increased mortality from cardiovascular disease, there is no reason to limit the intake of vitamin C-rich fruits and vegetables.

 

References

 1.         Osganian SK, Stampfer MJ, Rimm E, et al. Vitamin C and risk of coronary heart disease in women. J Am Coll Cardiol. 2003;42(2):246-252.

2.         Lee DH, Folsom AR, Harnack L, Halliwell B, Jacobs DR, Jr. Does supplemental vitamin C increase cardiovascular disease risk in women with diabetes? Am J Clin Nutr. 2004;80(5):1194-1200.

3.         MRC/BHF Heart Protection Study of antioxidant vitamin supplementation in 20,536 high-risk individuals: a randomised placebo-controlled trial. Lancet. 2002;360(9326):23-33.

4.         Waters DD, Alderman EL, Hsia J, et al. Effects of hormone replacement therapy and antioxidant vitamin supplements on coronary atherosclerosis in postmenopausal women: a randomized controlled trial. JAMA. 2002;288(19):2432-2440.

5.         Levy AP, Friedenberg P, Lotan R, et al. The effect of vitamin therapy on the progression of coronary artery atherosclerosis varies by haptoglobin type in postmenopausal women. Diabetes Care. 2004;27(4):925-930.

Thank you for your interest in our work.

Best regards,

Jane Higdon, Ph.D.

Linus Pauling Institute

Oregon State University

571 Weniger Hall

Corvallis, OR  97331

http://lpi.oregonstate.edu/infocenter