Ginkgo biloba may not be the herbal brain booster it has widely been believed to be, according to the results of a study published in the December 23/30 issue of JAMA.

The leafy green herb has been used in Chinese medicine for thousands of years, and more recently in Western culture as a dietary supplement for improving memory and cognitive function in aging adults.

But ginkgo biloba, when administered twice daily at a dose of 120 mg, showed no notable effect in reducing the incidence of dementia caused by Alzheimer’s disease or dementia overall in older adults when compared with placebo, according to the Ginkgo Evaluation of Memory (GEM) study (JAMA 2009;302:2663-70).

More than 3,000 adults aged 72-96 years were monitored at 6 medical centers in the United States between 2000 and 2008 in the largest completed randomized, double-blind, placebo-controlled dementia prevention trial to date, according to Beth E. Snitz, Ph.D., and her colleagues. A total of 60% of subjects successfully completed the study.

The median follow-up was 6.1 years, and 54% were men. Participants were randomized to receive a 120-mg dose of ginkgo biloba extract (n = 1,545) or placebo (n = 1,524) twice a day, noted Dr. Snitz of the department of neurology at the University of Pittsburgh. Follow-up included neuropsychological testing every 6 months until 2004 and once a year thereafter.

The placebo group performed better than did the ginkgo biloba group on 3 of 12 neuropsychological tests administered at baseline. Scores on other tests did not differ by treatment group.

The ginkgo biloba and placebo groups did not differ on rates of cognitive change for the global cognition score or cognitive domains tested (memory, attention, visuospatial abilities, language, and executive functions).

In year 6 of the study, a secondary analysis was taken and results were consistent with the primary analysis; rates of cognitive change for the global score and all cognitive domains did not differ by treatment group, the investigators noted. In participants with early dementia or symptoms of cognitive impairment, results also indicated that 3-4 years of ginkgo biloba treatment had no significant effect on cognitive decline 2-3 years after use.

The clinical meaning of cognitive decline in this study was defined by a 4-point change in the Alzheimer Disease Scale (ADAS-Cog).

“We [found] no evidence that G. biloba slows the rate of cognitive decline in older adults,” wrote the investigators. “These findings are consistent with previous smaller studies examining prevention of decline and facilitation of cognitive performance and with the 2009 Cochrane review of G. biloba for dementia and cognitive impairment.”

Funding for the study was provided in part through a grant from the U.S. National Center for Complementary and Alternative Medicine, a division of the U.S. National Institutes of Health. Ginkgo biloba extract tablets and placebo tablets were donated by Schwabe Pharmaceuticals.

Dr. Snitz and colleagues reported no relevant conflicts of interest.

Copyright (c) 2009 Elsevier Global Medical News. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

2009年12月23日发表在第30期《美国医学会杂志》(JAMA)上的一项研究结果表明，银杏可能并非普遍认同的促智草药。

 

这种多叶的绿色草药的中医应用已达数千年，而近期在西方，其被用作老年人的膳食补充剂以提高他们的记忆力和认知能力。

 

评价银杏对记忆作用(GEM)的研究发现，与安慰剂相比，每日2次应用120 mg 银杏提取物并未显著降低阿尔茨海默病引起的痴呆发生率或老年人总体痴呆的发生率(JAMA 2009;302:2663-70)。

 

Beth E. Snitz博士及其同事报告，该研究为迄今已完成的一项最大规模的有关痴呆预防的随机双盲安慰剂对照临床研究，研究者于2000~2008年对来自美国6个医学中心的3,000多例年龄介于72~96岁的受试者进行了监测。其中60%的受试者完成了研究。

 

该研究的中位随访时间为6.1年，54%的受试者为男性。匹兹堡大学神经科的Snitz博士介绍说，受试者被随机分配接受每日2次120 mg银杏提取物(1,545例)或安慰剂(1,524例)治疗。随访内容包括2004年前每6个月进行1次神经心理测试，其后每年测试1次。

 

在基线时进行的12项神经心理测试中，安慰剂组中有3项测试表现好于银杏提取物组。而在其他测试评分方面，两组间无差异。

 

就全球认知评分或受测认知领域(记忆力、注意力、视觉空间能力、语言及执行功能)而言，银杏与安慰剂组在认知变化率方面无差异。

 

研究者指出，在研究开始后6年时进行了二次分析，其结果与初次分析一致；两个不同治疗组在全球认知评分和所有认知领域方面的认知变化率无差异。对于患有早期痴呆或有认知损害症状的受试者，结果亦表明，3~4年的银杏提取物治疗对于治疗2~3年后发生的认知功能衰退无显著效果。

 

该研究中的认知功能衰退是根据阿尔茨海默病量表(ADAS-Cog)中的4点变化定义的。

 

研究者们报告：“我们未发现银杏可减慢老年人认知衰退率的证据。这些发现与之前进行的针对预防认知衰退和促进认知功能的小规模研究及关于银杏对痴呆和认知损害效果的2009 Cochrane综述的结果一致。”

 

该研究的资金部分来自于美国国家补充与替代医学中心(美国国立医学研究院的一个分支)的拨款。银杏提取物片和安慰剂片由Schwabe制药公司捐赠。

 

Snitz博士及其同事表示无利益冲突声明。

 

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