It can't just be the memorably exotic name nor the fact that Ginkgo biloba is a beautiful ornamental tree that has made it such a bestseller in the herbal pharmacopoeia. No, Ginkgo's success comes from hard-nosed clinical evidence of its benefits - as an antioxidant and anticoagulant, but principally as a relief for the dementias of old age.
In Germany, where the medical system allows doctors to prescribe herbal remedies, it's become the treatment of choice for Alzheimer's disease. In fact, it's become so popular there that, astonishingly, German doctors now write more prescriptions for Ginkgo than for any conventional pharmaceutical product.
It was in Germany in the 1950s that Ginkgo was first 'discovered', when botanist/physician Dr Willmar Schwabe made an extract from Ginkgo leaves from Japan. A sacred tree to Buddhists, Ginkgo had been known to Oriental medicine for millennia and cultivated for a variety of medicinal purposes - from asthma to tuberculosis.
Since then, over a thousand scientific studies have been conducted, mostly in Europe, on Ginkgo extracts, investigating its chemistry, pharmacology and clinical effects.
>From the start, it was Ginkgo's effect on the brain that attracted the most interest. During 1975-1997, 40 controlled trials were conducted on patients with 'cerebral insufficiency' disorders, such as senile dementia and Alzheimer's. Overall, these studies showed that Ginkgo could improve cognitive function by around 25 per cent (Adv Ther, 1998; 15: 54-65).
A US trial in old people's homes had results that are typical. Over 200 patients with either Alzheimer's or dementia due to mini-strokes were given 120 mg of Ginkgo every day for a year. Up to 37 per cent of the patients had significant improvements in both cognition and social functioning - obvious enough to be noticed by the staff. Ginkgo had the most effect in those with minor dementia but, even in severe cases, it managed appreciably to slow down the usual rate of deterioration (Neuropsychobiology, 2002; 45: 19-26).
Because of its lack of side-effects (see box), some geriatricians now prescribe Ginkgo in preference to tacrine, the only conventional drug known to benefit dementias. Interestingly, tacrine and Ginkgo have similar effects on brain function (Am J Ther, 1996; 3: 63-73). As a bonus, Ginkgo has also been found to help depression in the elderly - even in cases where conventional antidepressants haven't worked (Geriatr Forsch, 1993; 3: 45-53). Ginkgo has also helped memory loss caused by dementia (Psychiatr Serv, 2000; 51: 1130-4).
In the light of these results, Ginkgo has been suggested as a possible 'smart drug' to sharpen up everyone's mental performance, not just old people's. The evidence for this is almost as good. A team of scientists at the University of Northumbria carried out three separate studies on Ginkgo's effect on young people in their 20s. After just one dose of Ginkgo, there were almost immediate improvements in mental ability lasting for at least six hours (Psychopharmacology, 2000; 151: 416-23). This ties in with research in older adults, where Ginkgo was again found to boost mental performance, especially in people in their 50s (Phytother Res, 1999; 13: 408-15).
The findings are not all consistent, however. One study found that Ginkgo is 'largely ineffective' at improving memory (Physiol Behav, 2001; 73: 659-65).
Ginkgo's effects on the brain, particularly in the elderly, are thought to be mainly due to the ability of the plant extract to improve blood circulation through the brain's tiny capillary blood vessels (Antioxid Redox Signal, 1999; 1: 469-80). Recently, however, two further brain actions have been found. Ginkgo has a direct action on brain transmitters (Med Hypoth, 2000; 55: 491-3), and it has a protective effect on neurons, particularly in the hippocampus, the part of brain that is most damaged in Alzheimer's cases (Eur J Neurosci, 2000; 12: 1882-90).
Improved blood circulation may explain some of Ginkgo's other benefits, too. One of the problems that people with atherosclerosis (hardened arteries) often encounter is difficulty in walking. Pain in the legs can build up after a few yards, but a brief rest relieves it. The condition is called 'intermittent claudication'. Conventional drugs can't provide an 'optimal' answer, but Ginkgo can offer an alternative, says a recent review. Although not a cure for the condition, it appears to be at least as good as conventional drugs - but without the side-effects (Am J Med, 2000; 108: 276-81).
Glaucoma is another condition helped by Ginkgo and, here again, improved blood circulation may be the mechanism. There's increasing evidence that poor blood flow in the eye is one of the causes of glaucoma. Ginkgo appears to be the only agent capable of relieving it, with one study showing a 23 per cent increase in ocular blood flow (J Ocul Pharmacol Ther, 1999; 15: 233-40).
More exotically, Ginkgo's effects on circulation proved their worth to mountaineers. A Himalayan climbing expedition conducted what is probably the world's highest altitude clinical trial with Ginkgo tablets vs placebos at 16,000 feet. Ginkgo proved to be a real boon, preventing not only altitude sickness, but frostbite, too (Aviat Space Environ Med, 1996; 67: 445-52).
Ginkgo has also been shown to help women who suffer from premenstrual syndrome (PMS). In a double-blind, placebo-controlled trial, French doctors tested Ginkgo in more than 160 women with classical chronic PMS. After taking daily Ginkgo, starting on day 16 of the menstrual cycle and continuing to day 5 of the next, a dramatic decrease in symptoms was seen. Not only did the women have less breast tenderness and fluid retention, but the typical PMS mood was also improved. This decrease in 'neuropsychological symptoms' was objectively confirmed by the women's GPs (Rev Fr Gynecol Obstet, 1993; 88: 447).
In men, Ginkgo has been touted as a cure for impotence, but when scientifically tested in a placebo-controlled trial, this claim turned out to be a complete flop (J Urol, 1998; 159 [suppl 5]: 240).
Products and test results
Most of the world's supply of Ginkgo comes from plantations in China, southern France and the USA. The dried leaves are turned into Ginkgo extract, usually at a ratio of 50:1 (50 kg of leaves for 1 kg of extract). The extract can be used in the form of tablets, encapsulated powder or liquid tincture. All three forms are equally well absorbed by the body (Mater Med Pol, 1995; 27: 141-6).
Of the scores of Ginkgo products on the market - another indication of the extract's popularity - PROOF! has selected 12 of the leading brands for this road test.
As Ginkgo is made up of so many different chemical compounds (see box above), a full product analysis is not practicable. The herbal industry has thus agreed that certain chemical markers - namely, the flavonol glycosides (FGs; see box above) - may be used to indicate total Ginkgo content, as the FG content is believed to relate to the content of all the extract's other chemical constituents. FGs are now generally accepted as the chief yardstick of Ginkgo potency, with a content of 24 per cent FGs as the so-called 'standardised' figure. All of the Ginkgo clinical research has used preparations containing this percentage of FGs.
Given that 24 per cent FGs is now the universally accepted measure of quality, we rather expected that all Ginkgo products would meet this figure, at the very least. So, our laboratory's analyses came as a bit of a shock, with many of these high-street products falling below the standardised figure.
Moreover, compared with abroad, consumers here seem to be shabbily treated. In Germany, Ginkgo products contain FGs clustering around the 24 per cent figure. Even in the unregulated USA, the manufacturers there manage to attain that quality benchmark. A recent survey found that all the US retail Ginkgo products tested either met or exceeded 24 per cent FGs (J Pharm Pharmacol, 2002; 54: 661-9).
In our survey, however, a staggering eight of the 12 UK retail products failed to reach it. Also surprising is the discrepancy in quality among the products we tested - with neither price nor brand reputation serving as a guide. Indeed, some of the best-known names with the highest prices offered the worst-quality products.
So, full marks to Lamberts, Quest and Holland & Barrett for being up to international standards. As for the others, if they haven't provided a 'standardised' dose, they should at least tell the consumer what percentage of FGs their Ginkgo remedies do contain - not an onerous task as such a laboratory analysis is simple and relatively inexpensive.
Declaring the results on the label would help consumers make informed choices between rival products and, more important, it would allow users to know what doses of Ginkgo they are actually taking.
To draw up our Ginkgo league table, our lab analysed the flavonol glycoside content of each product, and calculated the cost of the therapeutic minimum 'standardised' dose of 120 mg of Ginkgo containing 24 per cent FGs, or 28.8 mg of FGs, per day.
Extra High Strength Ginkgo 6000mg
Price: lb8.95 for 60 120-mg tablets
This fairly high-priced product claims to provide 28.8 mg of flavonglycosides, which works out to exactly the standard 24 per cent FGs (in fact, the lab found the FG content to be marginally higher). Each tablet provides the therapeutic minimum dose of 120 mg and, at 15 p per dose, is the best value for money in our road test. This is an excellent product both in quality and price.
High Strength Ginkgo 2000mg
Price: lb5.95 for 60 40-mg tablets
The label states that each tablet provides 9.6 mg flavonglycosides - precisely 24 per cent FGs - although the lab found slightly less than that (9 mg). This is cheaper than Lamberts' 6000-mg bottle, but you need to take at least three tablets (at 10 p each) for a 28.8-mg FG dose so, in fact, this would cost you more. Nevertheless, it's a good buy.
Ginkgo Biloba 150mg Extract
Price: lb12.85 for 30 150-mg tablets
According to the label, one tablet provides 36 mg of 'Ginkgo flavonglycosides', which works out at exactly 24 per cent FGs, a figure confirmed by our laboratory. Each tablet costs 43 p, so a standard 120-mg dose would set you back 34 p.
Manufacturer: Nature's Plus
Price: lb11.95 for 60 120-mg vegicaps
The 'Combo' refers to the added ingredients in this product - vitamin E, capsicum and gotu kola. Our lab analyst found the Ginkgo quality to be quite high, with a respectable 22 per cent FGs. At 20 p per capsule, this product should have been in pole position, but it has lost one star because it fails to reach the FG standard.
Ginkgo Biloba 30 mg Standardized Extract
Manufacturer: Holland & Barrett
Price: lb4.49 for 30 30-mg tablets
The informative label tells you that each tablet contains 30 mg of 'Ginkgo Biloba Extract, standardised for a minimum of 24% Ginkgo Flavone Glycosides' - which turned out to be totally accurate. In fact, our laboratory found 25 per cent FGs. So, Holland & Barrett have produced something well up to international standards, but it's fairly pricey at 60 p for a 120-mg dose.
Ginkgo Biloba 520 mg
Price: lb14.39 for 100 520-mg capsules
'Full Potency Herbs' says the label from this highly reputable manufacturer. The small print is impressive, too: 'Each Vegicaps(R) provides: Ginkgo Biloba 520 mg (from ginkgo biloba leaf extract powder and 10 mg standardised ginkgo biloba leaf extract 50:1 [minimum 24% ginkgo flavoglycosides]).'
Such a detailed content analysis suggests a quality product that appears to meet the 24 per cent FG standard. But does it? Our lab found that each capsule contains 5.6 mg of FGs - barely 1 per cent (albeit satisfying the careful wording on the label).
So, to get the standardised 24 per cent FGs per 120 mg of extract (28.8 mg of FGs), you would need to take just over five capsules - at a cost of 72 p.
So, on cost alone, this would have merited only three stars, but we've marked it down even further because of the confusing label: the product does not contain a minimum of 24 per cent FGs and is thus certainly not 'full potency'.
Price: lb4.60 for 45 250-mg capsules
An unpretentious, low-price product - with good reason. Our lab found only 1 per cent FGs (2.6 mg per capsule), so to obtain the standard 28.8 mg of FGs, you would need to take 11 of these capsules and, at a cost of 10 p per capsule, that's over lb1.
Fresh Herb Extract Ginkgo Biloba
Price: lb7.49 for 50 mL
A liquid Ginkgo product claiming to contain 100 g of fresh Ginkgo extract. But our laboratory wasn't impressed. It could only find a mere 1.8 mg of FGs per mL. As the standardised dose contains 28.8 mg of FGs, you would need to take 16 mL of this tincture to achieve a therapeutic dose - at a rather hefty cost of lb2.40.
Ginkgo Biloba 900mg
Price: lb9.03 for 30 900-mg capsules
Here's another product claiming to be 'High Potency' on the label. Certainly, 30 capsules packed with the equivalent of 900 mg of powdered raw herb sounds like good value.
But the 'high potency' claim is empty. Our analysis shows 5.6 mg of FGs per capsule, and you'd need to take five to achieve the standardised 120-mg dose. This would set you back lb1.51.
Manufacturer: Higher Nature
Price: lb8.00 for 90 30-mg tablets
Another reputable manufacturer with a disappointing product, but with major claims on the label: 'guaranteed potency . . . ginkgo biloba extract powder (standardised 24% material)'. This sounds like the real McCoy, but our lab could detect only 0.8 mg of FGs per capsule - about 2.7 per cent, not 24 per cent. You would need to take a stomach-churning 36 capsules to achieve a therapeutic dose, at a cost of lb3.20.
Antioxidant Complex Ginkgo Plus
Price: lb18.45 for 90 150-mg capsules
BioCare has a reputation as a radical but responsible manufacturer and, as a result, has become something of a standard bearer for the alternative health movement.
Sadly, however, this product is a serious letdown. Our lab found that these capsules contain less than 1 per cent of FGs, a ludicrously low figure that would never get a look-in abroad. To get the standard 24 per cent FGs per 120 mg, you would need to swallow over 22 capsules - as well as the cost of lb4.51.
Manufacturer: Higher Nature
Price: lb3.90 for 30 30-mg tablets
Another Ginkgo product from the Higher Nature stable, this one is even more disappointing than the more expensive product. Again, the label claims that it contains 'standardised extract', but our lab could detect barely 1 per cent FGs. You'd need to consume 72 tablets in one go to get a single therapeutic dose - for a whopping lb9.36.
Research on dementias in the elderly has shown beneficial effects with Ginkgo at doses ranging from 120 mg to 240 mg a day. The effects may take a month to become evident and usually peak two months later (Curr Ther Res, 1998; 59: 881-8).
In younger people, a single dose in the morning has been shown to produce improved mental functioning for the rest of the day. The minimum dose appears to be 120 mg, rising to 360 mg - although, paradoxically, the higher doses may cause impairment of some cognitive tasks (Psychopharmacology, 2000; 151: 416-23).
In terms of safety, Ginkgo seems to be one of the most benign herbal remedies around. Most studies have shown that its side-effects are minimal (Altern Ther Health Med, 2001; 7: 70-87). However, problems may arise if Ginkgo is taken at the same time as some prescription drugs. The blood-thinning drug warfarin should be avoided, as Ginkgo is itself a natural anticoagulant. Ginkgo also interacts with thiazide diuretics and the antidepressant trazodone (Drugs, 2001; 61: 2163-75).
What is Ginkgo biloba made of? Pharmaceutical companies have studied the plant's chemistry intensively, hoping to discover a key active ingredient. But they've failed. One reason is that there are over a hundred different chemicals in Ginkgo. Also, as with many other herbs, the compounds appear to act synergistically. They have a greater medicinal benefit when combined than when separate - the whole is truly greater than the sum of its parts.
The biggest group of chemical compounds in Ginkgo are the flavonol glycosides (FGs), the chemicals that give the leaves their yellow colour. These FGs are the main source of Ginkgo biloba's powerful antioxidant and free radical-scavenging properties.
Another group of constituent chemicals are the terpenes, the most important of which are the ginkgolides and bilobalides. These compounds, unique to Ginkgo, are the ones which decrease blood viscosity ('thickness') and so improve circulation. In particular, ginkgolide B has been shown to have powerful inhibitory effects on platelet activating factor, the key component required to make the blood clot.