Veel supplementen lijken niet zinvol
Op basis van diermodellen en diverse studies bij mensen lijkt het erop dat bepaalde antioxidanten zinvol zijn bij het voorkomen van een aantal ziektes. De Cochrane groep onderzocht alle gepubliceerde studies en kwam tot een negatieve conclusie. Eenentwintig studies met 164439 gezonde vrijwilligers en zesenveertig studies met 68111 patienten met uiteenlopende ziekten werden bestudeerd. Het ging bij deze meta-analyse om studies naar de effecten van de volgende supplementen of vitamines: beta-caroteen, vitamine A, vitamine C, vitamine E en selenium.We geven de conclusie weer, er werden geen duidelijke aanwijzingen gevonden dat de supplementen een zinvolle bijdrage leverden. Voor vitamine C en selenium waren de resultaten minder negatief, en er wordt aanbevolen die twee supplementen verder te onderzoeken.[1]
Overall, the antioxidant supplements did not seem to reduce mortality. A total of 17880 of 136,023 participants (13.1%) randomised to antioxidant supplements and 10136 of 96527 participants (10.5%) randomised to placebo or no intervention died. In the analyses of the trials with low risk of bias, beta-carotene, vitamin A, and vitamin E significantly increased mortality.
There were no significant differences between the effects of antioxidant supplements in healthy participants (primary prevention trials) or participants with various diseases (secondary prevention trials).
Randomised trials with adequate bias control found no significant effect of vitamin C. In some of our analyses, selenium seems to reduce mortality.
The current evidence does not support the use of antioxidant supplements in the general population or in patients with certain diseases.
The combined evidence suggests that additional research on antioxidant supplements is needed.
The evidence on vitamin C and selenium was not conclusive. Future trials could focus on vitamin C and selenium and should assess both potential beneficial and harmful effects.
Conduct of additional primary and secondary prevention trials on vitamin A, beta-carotene, and vitamin E seems questionable, at least in the dosage range examined.
The present review does not assess antioxidant supplements for treatment of specific diseases (tertiary prevention), antioxidant supplements for patients with demonstrated specific needs of antioxidants, or the effects of antioxidants contained in fruits or vegetables. Further research and systematic reviews on these types of interventions are therefore warranted.
Sterfte juist hoger!
Verder in het oorspronkelijke document een bespreking door de auteurs van de verhoogde mortaliteit bij het chronisch innemen van bepaalde supplementen. We citeren:
Our systematic review contains a number of findings. Beta-carotene, vitamin A, and vitamin E given singly or combined with other antioxidant supplements significantly increase mortality. There is no evidence that vitamin C may increase longevity.
We lack evidence to refute a potential negative effect of vitamin C on survival.
Selenium tended to reduce mortality but only when high-bias risk trials were considered.
Accordingly, we need more research on vitamin C and selenium.
We confirmed that trials with inadequate bias control significantly overestimate intervention effects (Schulz 1995; Moher 1998; Kjaergard 2001; Bjelakovic 2004; Bjelakovic 2006).
The detrimental effect of antioxidant supplements became significantly more pronounced when we excluded all trials with potential confounding.
Our findings support and extend our previous findings regarding antioxidant supplements and increased mortality (Bjelakovic 2004).
Commentaar
Er zijn wel heel veel studies uitgesloten van de meta-analyse omdat die studies niet voldeden aan alle methodologische criteria. Dat is natuulijk altijd wat lastig, zeker als er honderden minder goed opgezette studies uitgesloten worden. Om te begrijpen hoe streng de studie was, voegen we een aantal literatuur referenties toe van de studies die niet in de meta-analyse werden meegnomen, omdat ze niet strak genoeg waren. En we beperken ons tot alleen de studies, waarvan de auteur met een A begon… Die slecht opgezette studies kwamen in het algemeen tot uitspraken die het geven van supplementen juist ondersteunen, aldus de auteurs. Nogmaals dat citaat: We confirmed that trials with inadequate bias control significantly overestimate intervention effects (Schulz 1995; Moher 1998; Kjaergard 2001; Bjelakovic 2004; Bjelakovic 2006).
Een ander meet biologisch aspect is ook belangrijk bij het interpreteren van de gegevens.
Wij zijn opgebouwd uit duizenden molecuulsoorten, en die komen ook in vruchten, noten, groenten en vlees voor. Al die moleculen hebben met elkaar een bepaalde relatie, en van sommigen zijn er veel, en van anderen minder. Om uit dat hele palet een enkele molecuulsoort te halen, en daar veel van te geven is natuurlijk ook wat kort door de bocht. De moderne systeembiologische visie op supplementen is ook, om meer volle of totale extracten van bepaalde planten te geven, om zo de natuurlijke balans tussen al die verschillende stoffen niet te veel te veranderen.
De uitkomsten van deze meta-analyse is in ieder geval voer voor discussie!
Uitgesloten literatuur van auteurs beginnend met A
| References to studies excluded from this review | |
| Abbey 1993 | |
| Abbey M, Nestel PJ, Baghurst PA. Antioxidant vitamins and low-density-lipoprotein oxidation. American Journal of Clinical Nutrition 1993;58:525-32.Links | |
| Adler 1993 | |
| Adler LA, Peselow E, Rotrosen J, Duncan E, Lee M, Rosenthal M, et al.Vitamin E treatment of tardive dyskinesia. American Journal of Psychiatry1993;150:1405-7. Links | |
| Aghdassi 1999 | |
| Aghdassi E, Royall D, Allard JP. Oxidative stress in smokers supplemented with vitamin C. International Journal for Vitamin and Nutrition Research1999;69:45-51. Links | |
| Aghdassi 2003 | |
| Aghdassi E, Wendland BE, Steinhart AH, Wolman SL, Jeejeebhoy K, Allard JP. Antioxidant vitamin supplementation in Crohn’s disease decreases oxidative stress. A randomized controlled trial. American Journal of Gastroenterology 2003;98(2):348-53. [MEDLINE: 12591053]. Links | |
| Aguilo 2004 | |
| Aguilo A, Tauler P, Fuentespina E, Villa G, Cordova A, Tur JA, et al.Antioxidant diet supplementation influences blood iron status in endurance athletes.International Journal of Sport Nutrition and Exercise Metabolism 2004;14:147-60. Links | |
| Akova 2001 | |
| Akova B, Surmen-Gur E, Gur H, Dirican M, Sarandol E, Kucukoglu S. Exercise-induced oxidative stress and muscle performance in healthy women: role of vitamin E supplementation and endogenous oestradiol. European Journal of Applied Physiology 2001;84:141-7. Links | |
| Al-Taie 2003 | |
| Al-Taie OH, Seufert J, Karvar S, Adolph C, Mork H, Scheurlen M, et al.Selenium supplementation enhances low selenium levels and stimulates glutathione peroxidase activity in peripheral blood and distal colon mucosa in past and present carriers of colon adenomas. Nutrition and Cancer2003;46:125-30. Links | |
| Albanes 1992 | |
| Albanes D, Virtamo J, Rautalahti M, Haukka J, Palmgren J, Gref CG, et al.Serum beta-carotene before and after beta-carotene supplementation. European Journal of Clinical Nutrition 1992;46:15-24. Links | |
| Alberts 2004 | |
| Alberts D, Ranger-Moore J, Einspahr J, Saboda K, Bozzo P, Liu Y, et al.Safety and efficacy of dose-intensive oral vitamin A in subjects with sun-damaged skin. Clinical Cancer Research 2004;10(6):1875-80. [MEDLINE: 15041701]. Links | |
| Allard 1994 | |
| Allard JP, Royall D, Kurian R, Muggli R, Jeejeebhoy KN. Effects of beta-carotene supplementation on lipid peroxidation in humans. American Journal of Clinical Nutrition 1994;59:884-90. Links | |
| Allard 1997 | |
| Allard JP, Kurian R, Aghdassi E, Muggli R, Royall D. Lipid peroxidation during n-3 fatty acid and vitamin E supplementation in humans. Lipids1997;32:535-41. Links | |
| Anah 1980 | |
| Anah CO, Jarike LN, Baig HA. High dose ascorbic acid in Nigerian asthmatics. Tropical and Geographical Medicine 1980;32:132-7. Links | |
| Anderson 1974 | |
| Anderson TW, Reid DB. A double-blind trial of vitamin E in angina pectoris. American Journal of Clinical Nutrition 1974;27(10):1174-8. [MEDLINE: 4214473]. Links | |
| Anderson 1975 | |
| Anderson TW, Beaton GH, Corey P, Spero L. Winter illness and vitamin C: the effect of relatively low doses. Canadian Medical Association Journal1975;112:823-6. Links | |
| Anderson 1997 | |
| Anderson D, Phillips BJ, Yu TW, Edwards AJ, Ayesh R, Butterworth KR. The effects of vitamin C supplementation on biomarkers of oxygen radical generated damage in human volunteers with "low" or "high" cholesterol levels. Environmental and Molecular Mutagenesis 1997;30:161-74. Links | |
| Anderson 1999 | |
| Anderson JW, Gowri MS, Turner J, Nichols L, Diwadkar VA, Chow CK, et al.Antioxidant supplementation effects on low-density lipoprotein oxidation for individuals with type 2 diabetes mellitus. Journal of the American College of Nutrition 1999;18:451-61. Links | |
| Andreone 2001 | |
| Andreone P, Fiorino S, Cursaro C, Gramenzi A, Margotti M, Di Giammarino L, et al.Vitamin E as treatment for chronic hepatitis B: results of a randomized controlled pilot trial. Antiviral Research 2001;49(2):75-81. [MEDLINE: 11248360]. Links | |
| Angstwurm 1999 | |
| Angstwurm MW, Schottdorf J, Schopohl J, Gaertner R. Selenium replacement in patients with severe systemic inflammatory response syndrome improves clinical outcome. Critical Care Medicine 1999;27(9):1807-13. [MEDLINE: 10507602]. Links | |
| Arad 2005 | |
| Arad Y, Newstein D, Roth M, Guerci AD. Rationale and design of the St. Francis Heart Study: a randomized clinical trial of atorvastatin plus antioxidants in asymptomatic persons with elevated coronary calcification. Controlled Clinical Trials 2001;22(5):553-72. [MEDLINE: 11578788]. Links | |
| * | Arad Y, Spadaro LA, Roth M, Newstein D, Guerci AD. Treatment of asymptomatic adults with elevated coronary calcium scores with atorvastatin, vitamin C, and vitamin E: the St. Francis Heart Study randomized clinical trial. Journal of the American College of Cardiology 2005;46(1):166-72. [MEDLINE: 15992652]. Links |
| Arvilommi 1983 | |
| Arvilommi H, Poikonen K, Jokinen I, Muukkonen O, Rasanen L, Foreman J, et al.Selenium and immune functions in humans. Infection and Immunity1983;41:185-9. Links | |
| Astley 1999 | |
| Astley S, Langrish-Smith A, Southon S, Sampson M. Vitamin E supplementation and oxidative damage to DNA and plasma LDL in type 1 diabetes.Diabetes Care 1999;22:1626-31. Links | |
| Avery 2003 | |
| Avery NG, Kaiser JL, Sharman MJ, Scheett TP, Barnes DM, Gomez AL, et al.Effects of vitamin E supplementation on recovery from repeated bouts of resistance exercise. Journal of Strength and Conditioning Research / National Strength & Conditioning Association 2003;17:801-9. Links | |
[1] Bjelakovic G, Nikolova D, Gluud LL, Simonetti RG, Gluud C. | Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases. | Cochrane Database Syst Rev. | 2008 Apr 16;(2):CD007176. doi: 10.1002/14651858.CD007176.
Toch wel zinvol:
AHA: Omega-6 Beneficial for Heart Health
The American Heart Association (AHA) released a new science advisory recommending that at least 5-10 percent of daily calories come from omega-6 polyunsaturated fatty acids. Other groups, including the European Commission (EU) and World Health Organization (WHO), have similar guidelines.
According to the advisory, published in Circulation: Journal of the American Heart Association, human and animal trials have shown that consuming this amount of omega-6 is associated with a decreased risk of coronary artery disease.
The safety of omega-6 fatty acids has been debated, as some researchers suggested that they might actually increase the risk of heart disease. This is because a major component of omega-6 fatty acids is linoleic acid, which can be converted to arachidonic acid, a building block for some inflammation-related molecules.
William Harris, director of the Metabolism and Nutrition Research Center of the University of South Dakota Sanford School of Medicine, led the AHA’s two-year assessment. The authors analyzed a meta-analysis of randomized, controlled trials and more than two dozen observational, cohort, case/control and ecological studies.
The AHA committee found that in most trials, omega-6 fatty acids either did not change or lowered levels of inflammatory markers.
According to observational trials, people who consumed the most omega-6 fatty acids typically developed the fewest cases of heart disease. Other studies found that patients with heart disease generally had lower levels of omega-6 in their blood.
In controlled trials comparing the number of heart attacks in patients eating high or low levels of omega-6, those who ate more omega-6 fatty acids developed fewer cases of heart disease.
According to the AHA advisory, most Americans already eat the recommended amount of omega-6 fatty acids. Recommended daily doses range from 12 to 22 grams, depending on a person’s age, gender and level of physical activity.
For more information about omega-6 fatty acids, please visit Natural Standard’s Foods, Herbs & Supplements database.
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References:
American Heart Association (AHA). http://www.americanheart.org
Harris WS, Mozaffarian D, Rimm E, et al. Omega-6 Fatty Acids and Risk for Cardiovascular Disease. A Science Advisory From the American Heart Association Nutrition Subcommittee of the Council on Nutrition, Physical Activity, and Metabolism; Council on Cardiovascular Nursing; and Council on Epidemiology and Prevention. Circulation. 2009 Jan 26. View Abstract
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