濫用維生素營養補充劑提高死亡率

濫用維生素營養補充劑提高死亡率作者：益民　　國際權威醫學刊物《美國醫學會雜誌》（Journal of American Medical Association）在2007年2月28日出版的一期中發表了一篇綜合比較-分析論文，對1990年至2005年10月國際上發表的68項關於維生素營養補充劑與若干疾病死亡率之間關係的論文進行了系統分析，得出的結論令人吃驚：服用抗氧化類維生素營養補充劑對降低死亡率沒有任何幫助，其中人們常用的維生素A、維生素E和胡蘿蔔素等反而會顯著提升死亡率：服用維生素A的人死亡率提高4%；服用維生素E死亡率提高16%；服用胡蘿蔔素的死亡率提高7%；服用維生素C對死亡率沒有影響（無論好壞）。但該報告沒有給出死亡提高的直接原因。　　富含抗氧化劑的維生素被認為能夠延緩某些人體器官組織（如心血管）的老化、甚至具有一定的抗癌變功能。但國際上亦有研究認為維生素的功能只有以食物形態（如蔬菜、水果、穀物）被攝取才能被人體有效吸收，而加工成片劑形態的營養補充劑則難以被人體吸收。但迄今為止鮮有大規模、權威的研究能夠確認長期服用維生素營養補充劑會提高服用者的死亡率。　　主導此項研究的是設在丹麥哥本哈根大學醫院的科克蘭肝膽病審核小組（Cochrane Hepato-Biliary Group）。該小組是國際權威的醫學研究循證組織---科克蘭合作機構（Cochrane Collaboration）---下設的專業審核小組之一。科克蘭合作機構是由世界90多個國家的1萬多名權威醫學專家自願組成的非營利機構，下設50多個專業審核小組，在世界90多個國家設有可克蘭中心，每年發表大量專項研究報告，對各種醫療產品和技術的有效性和證據進行獨立的論證。　　該研究將68項（涉及23萬多人）相關研究分為「低偏差」和「高偏差」兩類。對兩類研究綜合（即不分類）比較分析的結果表明，服用維生素與死亡率沒有明顯的相關關係，但剔除可靠度較差的「高偏差」類研究，僅對「低偏差」類的47項研究（涉及18萬多人）的分析結果則顯示，長期服用維生素會顯著增加死亡的風險。　　註：以上信息編自美聯社、路透社、新聞周刊等刊物的網路版。下面是《美國醫學會雜誌》刊登的該研究的摘要。因本人非該刊物訂閱者，故沒有閱讀到研究報告的全文。Mortality in Randomized Trials of Antioxidant Supplements for Primary and Secondary PreventionSystematic Review and Meta-analysisGoran Bjelakovic, MD, DrMedSci; Dimitrinka Nikolova, MA; Lise Lotte Gluud, MD, DrMedSci; Rosa G. Simonetti, MD; Christian Gluud, MD, DrMedSci JAMA. 2007;297:842-857. Context Antioxidant supplements are used for prevention of several diseases. Objective To assess the effect of antioxidant supplements on mortality in randomized primary and secondary prevention trials. Data Sources and Trial Selection We searched electronic databases and bibliographies published by October 2005. All randomized trials involving adults comparing beta carotene, vitamin A, vitamin C (ascorbic acid), vitamin E, and selenium either singly or combined vs placebo or vs no intervention were included in our analysis. Randomization, blinding, and follow-up were considered markers of bias in the included trials. The effect of antioxidant supplements on all-cause mortality was analyzed with random-effects meta-analyses and reported as relative risk (RR) with 95% confidence intervals (CIs). Meta-regression was used to assess the effect of covariates across the trials. Data Extraction We included 68 randomized trials with 232 606 participants (385 publications). Data Synthesis When all low- and high-bias risk trials of antioxidant supplements were pooled together there was no significant effect on mortality (RR, 1.02; 95% CI, 0.98-1.06). Multivariate meta-regression analyses showed that low-bias risk trials (RR, 1.16; 95% CI, 1.05-1.29) and selenium (RR, 0.998; 95% CI, 0.997-0.9995) were significantly associated with mortality. In 47 low-bias trials with 180 938 participants, the antioxidant supplements significantly increased mortality (RR, 1.05; 95% CI, 1.02-1.08). In low-bias risk trials, after exclusion of selenium trials, beta carotene (RR, 1.07; 95% CI, 1.02-1.11), vitamin A (RR, 1.16; 95% CI, 1.10-1.24), and vitamin E (RR, 1.04; 95% CI, 1.01-1.07), singly or combined, significantly increased mortality. Vitamin C and selenium had no significant effect on mortality. Conclusions Treatment with beta carotene, vitamin A, and vitamin E may increase mortality. The potential roles of vitamin C and selenium on mortality need further study. Author Affiliations: The Cochrane Hepato-Biliary Group, Copenhagen Trial Unit, Center for Clinical Intervention Research, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark (Drs Bjelakovic, L. L. Gluud, Simonetti, and C. Gluud and Ms Nikolova); Department of Internal Medicine, Gastroenterology and Hepatology, University of Nis, Nis, Serbia (Dr Bjelakovic); and Divisione di Medicina, Ospedale V. Cervello, Palermo, Italy (Dr Simonetti). Source: http://jama.ama-assn.org/cgi/content/abstract/297/8/842
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