Multivitamins offer almost no benefit in preventing chronic disease 'and they should be avoided,' experts said Monday in releasing the results of two new clinical trials.
The rigorously conducted studies, published in the Annals of Internal Medicine, showed multivitamins had no effect on cognitive function or cardiovascular health. They are the latest in a series of reports-including a review last month of 26 vitamin studies-indicating that supplements have little health benefits in generally well-nourished, Western populations.
'The message is simple: Most supplements do not prevent chronic disease or death, their use is not justified, and they should be avoided,' four physicians and public health experts wrote in an editorial accompanying the studies.
The editorial added that beta-carotene, vitamin E and possibly high doses of vitamin A increased the risk of death in some other trials.
The global vitamin industry is huge, with sales last year of $23.4 billion, up 3% from 2011, according to Euromonitor International. Sales of multivitamins specifically rose 2.5% last year, to $14.2 billion. About 40% of Americans reported taking multivitamins or minerals between 2003 and 2006, the most recent data available, according to the Centers for Disease Control and Prevention.
Vitamin-industry groups criticized the editorial, and pointed to a study last year of 15,000 men, which indicated that daily use of a multivitamin modestly reduced the risk of cancer. Some experts consider the results an outlier.
'It's no secret that many consumers in this country don't get the recommended nutrients from their diet alone, and multivitamin and mineral supplements are an affordable alternative,' said John Shaw, executive director of the Natural Products Association, a trade group.
One of the new trials assessed how vitamins affected cognitive function in 5,947 male physicians aged 65 years or older. Participants were given either a daily multivitamin-PfizerInc.'s Centrum Silver-or placebo pills, and their cognitive function was assessed at the outset and again up to three times during a 12-year period. Researchers found no difference in the mean cognitive change over time between the vitamin and placebo groups.
Francine Grodstein, a professor of medicine at Harvard University and Brigham and Women's Hospital in Bostonwho led the study, called the results disappointing, but said she wasn't ready to write off vitamins to the same extent as the editorial writers. Longer studies or trials in less highly educated populations with poorer diets could yield different results, she said.
Pfizer said multivitamins such as Centrum Silver are 'primarily intended to help people fill dietary gaps when they aren't fulfilling their nutritional needs through food alone, and are not intended to diagnose, treat, cure or prevent any disease.'
The second trial involved 1,708 patients aged 50 or older who had suffered a heart attack at least six weeks earlier. They were given either high-dose multivitamins or a placebo. The study showed that taking vitamins didn't reduce a patient's risk of dying or of suffering further cardiovascular problems, such as heart attack or stroke.
Researchers who led that study said it was somewhat undermined by patients withdrawing from the trial or failing to take their vitamins or placebos.
Gervasio Lamas, a Columbia University cardiologist who led the study, said he has been telling his patients 'for decades' not to take vitamins. 'We're not taking care of patients with nutritional deficiency. I've never seen a patient with scurvy or beriberi,' he said, referring to diseases caused by deficiencies in vitamins C and B1. 'If you're a healthy person trying to stay healthy, the money is in stopping smoking, exercising, losing weight' and taking any prescriptions for hypertension or cholesterol, he said.
Dr. Lamas and others noted that certain vitamins and minerals have proved beneficial in targeted populations. Folic acid, for instance, is widely recommended to pregnant women to prevent birth defects of the brain or spine. And the possible benefits of vitamin D in preventing falls among the elderly require further study, according to the authors of the editorial.
Multivitamins also have shown benefit in malnourished populations in Africa and Asia, public health experts said.
The latest clinical trials follow a review published last month in the same medical journal, which examined 26 studies on the effects of vitamin and mineral supplements in chronic disease. The researchers said they found 'no consistent evidence that the included supplements affected [cardiovascular disease], cancer, or all-cause mortality in healthy individuals without known nutritional deficiencies.'
The study last year that showed Centrum Silver produced a modestly lower risk of cancer among 15,000 men left doctors divided. Lawrence Appel, a professor of medicine at Johns Hopkins University who helped write the anti-vitamin editorial, called the result a 'very tiny effect,' one that didn't sway his overall view on supplements.
2013年 12月 17日 12:03
研究發現服用復合維生素幾乎沒有益處
在
周一公布了兩項新臨床試驗的結果后，專家說，復合維生素對于預防慢性疾病幾乎沒有什么益處，應當避免服用復合維生素。《內 科醫學年鑒》(Annals of Internal Medicine)刊登了上述嚴格進行的研究。研究顯示，復合維生素對認知功能或心血管健康沒有影響。這也是表明食物補充劑對于普遍營養良好的西方人群幾 乎沒有什么健康益處的最新報告。此前已有一系列報告得出這樣的結論，包括上個月對26項維生素研究的回顧。
四位醫師和公共健康專家在伴隨研究發布的評論中寫道：傳遞出的信息很簡單，那就是大多數食物補充劑無法預防慢性疾病或死亡，并沒有服用它們的正當理由，應當避免服用。
評論補充說，在其他一些試驗中，β胡蘿卜素、維生素E以及還可能包括高劑量的維生素A會增加死亡的風險。
市 場研究機構歐睿信息咨詢有限公司(Euromonitor International)的數據顯示，全球維生素產業十分龐大，去年銷售額達到234億美元，較2011年提高了3%。具體而言，復合維生素的銷售額 去年增長了2.5%，達到142億美元。疾病控制和預防中心(Centers for Disease Control and Prevention)最新的數據顯示，大約40%的美國人報告說他們在2003年至2006年間服用復合維生素或礦物質。
維生素行業組織對上述評論提出批評，并指出去年一項對1.5萬名男性的研究表明，每日服用適量復合維生素可以降低患癌風險。一些專家認為上述研究結果不具代表性。
行業組織天然產品協會(Natural Products Association)的執行董事肖(John Shaw)說，這個國家的許多消費者僅靠他們攝入的食物無法獲取建議的營養，而復合維生素及礦物質補充劑是一種可以負擔得起的替代選擇。
新 試驗之一評估了維生素如何影響5,947名65歲及以上年齡男性醫師的認知功能。參加試驗者被分為兩組，每天分別給他們輝瑞公司(Pfizer Inc.)生產的復合維生素善存銀片(Centrum Silver)或安慰劑。他們的認知功能在試驗之初會被評估，之后在12年的時期內再至多評估三次。研究人員發現，試驗期內，服用復合維生素和安慰劑的兩 組人在平均認知功能的改變方面沒有區別。
哈佛大學(Harvard University)和布里格姆婦女醫院(Brigham and Women's Hospital)的醫學教授Francine Grodstein領導了上述研究。她稱研究結果令人失望，但說她并不準備像評論作者推薦的那樣放棄維生素。她說，如果進行更長時間的研究，或者對教育程 度不太高、飲食攝入情況不太好的人群進行試驗，可能會得出不同的結果。
輝瑞說，善存銀片等復合維生素的主要目的在於幫助人們彌補通過飲食攝入的營養不足的情況，而不是為了診斷、治療、治愈或是預防任何疾病。
第 二個試驗有1,708名年齡在50歲及以上的患者參與，這些人全都在至少六周前發作過一次心臟病。他們之中一部份人拿到的是大劑量的復合維生素，另一部份 人拿到的是安慰劑。這份研究表明，服用維生素並不能降低患者死亡或未來發生心血管問題——比如心臟病或突發中風——的風險。
不過領導這項研究的研究人員說，有些患者退出了試驗，有些患者沒有服用維生素或安慰劑，使得該研究多少打了點折扣。
領 導這次研究的哥倫比亞大學(Columbia University)的心臟病學家拉馬斯(Gervasio Lamas)說，他幾十年來一直告誡他的病人不要服用維生素。他說，我們治療的不是營養不良的患者，我從沒見過哪個病人患有壞血病或腳氣。他提到的這兩種 病是因為維生素C和維生素B1缺乏造成的。他說，如果一個健康的人想要保持健康的話，應該做的是停止吸煙、鍛煉身體、降低體重，如果有高血壓或膽固醇偏高 的話，就按醫囑服藥。
拉馬斯和其他研究人員指出，特定維生素和礦物質已經被證明對目標人群有益。比如，葉酸就被廣泛推薦給孕婦服用，用以預防新生兒在大腦或是脊柱方面的缺陷。評論文章的作者指出，維生素D在防止老年人跌倒方面的可能益處還需要進一步的研究。
公共健康專家們說，研究表明復合維生素對非洲和亞洲的營養不良人群有益處。
在上述最新臨床試驗之前，同一份醫學期刊曾于上月發表了一篇評論文章，該文對26項研究（有關維生素和礦物補充劑對慢性病的作用）進行了分析。研究人員說，他們發現，對沒有已知營養缺陷的健康個人而言，沒有一致的證據表明，補充劑對心血管疾病、癌癥或全因死亡率有影響。
去 年對1.5萬人進行的、表明善存銀片可輕微降低罹患癌癥幾率的研究在醫生之間引發了分歧。美國約翰‧霍普金斯大學(Johns Hopkins University)的藥學教授阿佩爾(Lawrence Appel)稱這一結果顯示出的只是“微乎其微的影響”，並沒有改變他對補充劑的整體觀點。阿佩爾幫助撰寫了這篇反對服用維生素的評論文章。
JEANNE WHALEN
沒有留言:
張貼留言