Tuesday June 17 2008
Leaves of the Ginkgo biloba (maidenhair tree)
A study has found that Ginkgo biloba does not improve mental function or quality of life in people with dementia, reports The Daily Telegraph and other news sources. The newspaper suggests that about “one in 10 people with dementia take Ginkgo biloba after some studies showed it may have a small effect on their symptoms”.
The study included 176 people with mild-to-moderate dementia who received daily doses of either Ginkgo or an inactive placebo for six months. Using a standard test of mental function, the study found no difference between the groups. The Telegraph described the Alzheimer's Society-funded study as “one of the longest and most rigorous ever conducted on Ginkgo biloba”.
The study on which these stories are based was well conducted and provides good evidence that Ginkgo does not improve cognitive function or quality of life in those with mild-to-moderate dementia.
Where did the story come from?
Dr Rob McCarney and colleagues from Imperial College London, the Royal London Homeopathic Hospital, University College London, London School of Hygiene and Tropical Medicine and the International Institute for Integrated Medicine in France carried out this research. The study was funded by the Alzheimer’s Society. It was published in the peer-reviewed medical journal: International Journal of Geriatric Psychiatry.
What kind of scientific study was this?
This was a double-blind randomised controlled trial, which looked at the effects of Ginkgo biloba on people with dementia. This was a pragmatic trial, which means it tried to use conditions that were as representative of normal clinical practice as possible.
The researchers enrolled 176 adults aged 55 or above with mild-to-moderate dementia from London and surrounding areas. Potential participants were recruited by a referral from a GP or other health professional or via advertisements in newspapers, newsletters and posters. People who had used Ginkgo in the previous two weeks were excluded from the trial, as were people who had started to take cholinesterase inhibitors in the previous two months. Also excluded were people with known bleeding abnormalities and those taking warfarin (because Ginkgo had been linked with a risk of bleeding).
Eligible people were randomly assigned to receive either a standardised Ginkgo extract tablet (EGb 761, two 60mg tablets daily) or an inactive, but identical-looking, placebo tablet for six months. Participants could take other medications during the trial, but were withdrawn from the study if they had to start taking cholinesterase inhibitors. The researchers measured participants’ cognitive function, using a standard assessment tool (ADAS-Cog). They also assessed the participants’ quality of life, using standard questionnaires completed by either the participant themselves or their carer. Researchers also asked about any additional medications that the participants were taking. Participants were randomly assigned to two types of follow-up: to receive assessments only at the start of the study and at six months (minimal follow-up) or to receive assessments at these points in time, as well as after two and four months (standard follow-up) to see if this affected the findings.
The researchers compared cognitive function between the Ginkgo and placebo groups, taking into account the participants’ scores at baseline. Three different analyses were carried out. The main analysis included all participants and it used statistical methods to estimate any missing data. The second analysis included only participants with complete data. The third included only those participants who had taken at least 80% of the study medication, had completed all assessments and had complete data.
What were the results of the study?
After six months, there was no difference in cognitive abilities between people receiving Ginkgo and people receiving the placebo. There was also no difference between the Ginkgo and placebo groups in quality of life, as rated by either the participants themselves or their carers. Results were the same for all three methods of analysis adopted by the researchers. Results did not differ between participants with minimal and standard follow up.
What interpretations did the researchers draw from these results?
The researchers concluded that they found “no evidence that a standard dose of high-purity Ginkgo biloba confers benefit in mild-moderate dementia over six months.”
What does the NHS Knowledge Service make of this study?
The strengths of this study include its random allocation of participants, use of a placebo and double blinding. However, there were some limitations:
- The trial was smaller than planned, which may mean that clinically important differences in cognitive ability or quality of life might not have been detected by statistical tests. However, the results did not indicate any tendency towards better performance with Ginkgo and this makes it more unlikely that a larger trial would show any benefit of Ginkgo either.
- The placebo group had slightly worse cognitive function (assessed using the ADAS-Cog) at baseline than the Ginkgo group. The researchers took this difference into account when analysing the results.
- The study aimed to be representative of normal clinical practice and therefore accepted the clinicians’ diagnoses of dementia (rather than requiring the use of a standardised diagnostic scale) and included all eligible dementia patients (rather than only accepting participants with one specific type of dementia e.g., Alzheimer’s disease). So although the results may be representative of the typical mixed dementia population seen in clinical practice, they may not be representative of what might be seen in a group of people with a single type of dementia diagnosed using standard tests.
The results of this study suggest that Ginkgo biloba does not improve cognitive function in people with mild–to-moderate dementia.
Sir Muir Gray adds...
It is always helpful to know what does not work, as well as knowing what does.