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在一篇有关银杏的前驱随机试验中，相较于服用安慰剂者，服用此类补充剂3年的年长病患有半数发生记忆问题；不过，此结果未达统计上的显著差异。
研究者表示，这对银杏的保护效果缺乏证据，可能是因为参与此研究的样本数相对较少，且研究期间短。
奥勒冈州立大学、老化研究健康中心公共卫生部的Hiroko H. Dodge博士表示，我们必须说，本研究的结论尚不确定。
Dodge博士向Medscape神经学&神经外科学表示，她对研究结果仍感到些微鼓励，特别是她和同事发现控制了服药顺从性时；虽然没有统计上的显著意义，我们显示了一个前溯趋势，相较于服用安慰剂者，依照指示服用银杏的病患只有少数发生轻微的认知问题。
她们的研究发现线上登载于2月27日的神经学期刊。
【一个紧迫的问题】
因为族群年纪和85岁以上者渐增，研究者热切的希望发现一种可以抵抗认知衰退的制剂；社会所面临的紧迫公共卫生问题之一就是人口数迅速增加，平均年纪也增加，发生失智的风险也增加。
银杏用于医疗已经有数百年，且价格不贵；之前的证据认为它对控制一些失智症有效，本研究是第一个有关银杏的随机控制试验，探究预防失智的问题。
这个双盲前驱试验包括了118名85岁以上的记忆功能正常的年长者，这些人的简易智能状态检查量表(MMSE)分数大于23且临床失智评估量表(CDR)为0。
研究在奥勒冈健康与科学大学的NIA-Layton老化与阿兹海默症中心、神经异常辅助医疗奥勒冈中心进行。
受过训练的人员完成电话与居家访问，验血以筛检失智症的共同原因，完成脑部磁震造影扫描；研究对象被随机分派接受标准化银杏粹取物(GBE)一天3次(总量240 mg)或者安慰剂。
在常规的追踪访视中，研究者回顾参与者的健康状态、MMSE、忧郁症状、日常生活活动力、药物与病史等；这些人每年接受认知检测，包括由神经科医师进行CDR，研究搜集的资料期间达42个月。
在研究期间，有 21位 (17.8%) 的CDR 变成 0.5，其中14 名属于安慰剂组，7名属于GBE组；这21名之中，有18位至少有2次连续的CDR分数0.5，有4 名的CDR达到 1.0以上 (3名属于安慰剂组， 1名属于GBE组)；GBE组有16人死亡(26.6%)，安慰剂组有13人死亡(21.6%)。
以安慰剂组作为对照，GBE组的CDR变成0.5的风险比为 0.43；这未达统计上的显著差异。
【适当服用药物治疗者的记忆损失较小】
整体而言，68.6%的参与者达到研究定义的服药顺从性：GBE组有65.0%，安慰剂组有72.4%；研究者发现，银杏组的病患且适当服用药物者，和安慰剂组相比，发生轻微记忆问题的风险较低(CDR从0变成0.5的风险比为 0.33)。
Dodge医师表示，这是令人感到鼓舞的结果，我们认为次级分析有比较清楚的结果，因为我们控制了服药顺从程度，但是在临床试验中，我们必须报告未经校对过的最初结果。
【银杏组有比较多中风】
两组之间的不良反应没有整体差异，但是在GBE组有6件中风和1件短暂性脑缺血发作，安慰剂组没有类似案件；除了缺血性中风之外，都不严重(都未导致死亡)；增加的中风风险需要在其他的GBE研究中进行后续的密切观察，不过，Dodge医师表示，服用银杏者有比较高的中风率可能只是凑巧。
Dodge医师表示，本研究的结果需要用更大型的研究来厘清；匹兹堡大学已经进行对3,000名病患的5年追踪银杏研究，今年底将可望有结果。
本研究接受辅助替代医疗国家研究中心以及国家老化研究中心之赞助；作者报告没有利益冲突 。
Neurology 2008; 线上发表于2008年2月27日。 摘要。
Effects of Ginkgo Biloba on Memory Still Not Clear
By Pauline Anderson
Medscape Medical News
In a pilot randomized trial of ginkgo biloba, half as many elderly patients taking this supplement for over 3 years developed memory problems compared with those taking placebo. However, this result did not reach statistical significance.
This lack of proven protective effect of ginkgo biloba could be due to the relatively small number of participants in this pilot study and to its short duration, the researchers speculate.
"We have to say that it [the study] is inconclusive or not clear-cut," said Hiroko H. Dodge, PhD, from the department of public health and Center for Healthy Aging Research at Oregon State University, in Corvallis.
Dr. Dodge told Medscape Neurology & Neurosurgery that she is still "quite encouraged" by the study results, especially those she and her colleagues found when they controlled for medication adherence. "Even though it was not statistically significant, we showed a protective trend" in that fewer patients taking ginkgo biloba as directed went on to develop mild cognitive problems compared with patients on placebo, said Dr. Dodge.
Their findings are published online February 27 in Neurology.
A Pressing Problem
As the population ages and the number of people aged 85 years and older increases, researchers are keen to find an agent that protects against cognitive decline. "One of the most pressing public health problems facing our society is the rapidly growing number of people who, due to their age alone, are at high risk of developing dementia," the authors write.
Ginkgo biloba is readily available and relatively inexpensive and has been used medicinally for thousands of years. Previous evidence suggested that this herb is effective in the management of some dementias. This study was the first randomized, controlled trial of ginkgo biloba that looked at prevention of dementia, said Dr. Dodge.
The double-blind pilot trial included data on 118 people aged 85 years or older with normal memory function. Participants had to have a Mini Mental State Examination Score (MMSE) of greater than 23 and a Clinical Dementia Rating (CDR) of 0.
The study was carried out at the Oregon Health & Science University's NIA-Layton Aging & Alzheimer's Disease Center and the Oregon Center for Complementary and Alternative Medicine in Neurological Disorders.
Trained personnel completed telephone and in-home interviews, took blood samples to screen for common causes of dementia, and completed a magnetic resonance imaging scan of the brain. Subjects were randomly assigned to receive either standardized ginkgo biloba extract (GBE) taken 3 times a day (for a total of 240 mg) or placebo.
During regular follow-up visits, researchers reviewed the participants' health status, MMSE, depressive symptoms, activities of daily living, medications, and health history. Subjects received extensive cognitive testing every year, including a CDR from a neurologist. The study included data for up to 42 months.
Over the course of the study, 21 subjects (17.8%) progressed to a CDR of 0.5, of whom 14 were in the placebo and 7 in the GBE group. Of the 21 cases, 18 had at least 2 consecutive CDRs of 0.5, and 4 progressed to CDR of 1.0 or greater (3 among the placebo and 1 among the GBE group). There were 16 deaths (26.6%) in the GBE group and 13 deaths (21.6%) in the placebo group
With the placebo group as a reference, the hazard ratio of GBE on progression to CDR = 0.5 was 0.43. This effect did not reach the predefined statistical significance.
Less Memory Decline in Those Taking Medications Properly
Overall, 68.6% of participants met the study definition of medication adherence: 65.0% among the GBE group and 72.4% among the placebo group. The researchers found that the patients in the ginkgo group who took their medications properly had a lower risk of developing mild memory problems than those taking a placebo (hazard ratio of 0.33 for progression from CDR = 0 to CDR = 0.5.)
This was an encouraging result, said Dr. Dodge. "We feel the secondary analysis has clearer results because we're controlling the adherence level, but in a clinical trial, we have to report the first result without adjusting anything."
More Strokes in Ginkgo Group
There was no overall difference in adverse events reported by subjects in either group, but there were 6 strokes and 1 transient ischemic attack in the GBE group, while there were no such events in the placebo group. All but 1 of these strokes were ischemic, but none were severe (no strokes led to death). "The increased stroke risk will require further close scrutiny in other GBE prevention trials," the authors wrote. However, this higher stroke rate among patients taking ginkgo could, again, "just be chance," said Dr. Dodge.
The results of this research need to be clarified with larger studies, said Dr. Dodge. Results of a much larger ginkgo study being carried out at the University of Pittsburgh that has been following 3000 subjects for 5 years should be available by the end of this year, she said.
The study was supported by the National Center for Complementary and Alternative Medicine and the National Institute on Aging. The authors report no conflicts of interest.
Neurology 2008; Published online February 27, 2008. Abstract