August 2018 Issue

Supplements: Ginkgo Biloba Extract
By Jessica Levings, MS, RD
Today's Dietitian
Vol. 20, No. 8, P. 14

Long used in the United States as a popular dietary supplement marketed for improving memory and cognitive function, Ginkgo biloba extract is derived from the leaves of the Ginkgo biloba tree; common names include ginkgo, Ginkgo biloba, fossil tree, maidenhair tree, Japanese silver apricot, baiguo, and yinhsing.1 In the United States, ginkgo extract is sold as an oral over-the-counter herbal supplement in forms such as capsules, tablets, teas, and liquid extracts. While there's currently no recommended dose of supplemental Ginkgo biloba, experts suggest starting at 120 mg daily and increasing gradually to the desired intake level. Total daily doses in clinical trials and prescriptions from health care providers range from 120 to 240 mg for treatment of Alzheimer's disease and vascular dementia, 240 mg for healthy adults aiming to improve memory function, and between 120 and 600 mg for those aiming for improved cognitive function.2 As with many drugs and supplements, a small percentage of individuals has reported minor side effects when taking ginkgo extract including nervousness, headache, and stomachache. In the United States, the National Toxicology Program (NTP) regulates ginkgo, but current federal law doesn't require dietary supplements to undergo the same premarket testing for safety or efficacy as pharmaceutical drugs.

Ginkgo extract is marketed for improving myriad conditions such as memory and brain function due to its ability to improve circulation and blood flow to the brain, according to the National Institutes of Health. However, studies testing the efficacy of ginkgo extract haven't produced consistent evidence of any benefit for any medical condition.1

Efficacy
According to the NTP, studies haven't consistently found that ginkgo extract improves brain function; more research is needed. In the largest clinical trial of Ginkgo biloba extract to date, the Ginkgo Evaluation of Memory study, researchers assessed data on 3,069 people aged 75 and older with normal cognition or mild cognitive impairment. One-half of the participants took 120 mg of ginkgo extract twice daily for nearly six years, and the other half didn't. The results showed that 240 mg of ginkgo extract over six years wasn't effective in reducing the incidence of dementia or lessening cognitive decline in either people with normal cognition or those with mild cognitive impairment.3 However, a 52-week trial administering 120 mg of ginkgo extract daily to patients with mild to severe dementia or Alzheimer's disease found that it was effective in stabilizing and in many cases improving cognitive performance and social functioning.4 Furthermore, a 24-week trial administering 240 mg of ginkgo extract or placebo daily to patients with presenile and senile Alzheimer's- and stroke-related dementia also was found to improve memory.5

A review of 30 clinical trials examining the effect of Ginkgo biloba on people with acquired cognitive impairment including dementia found benefits associated with Ginkgo extract at a dose greater than 200 mg/day (but not for a lower dose) after 24 weeks and found benefits to cognition after taking the ginkgo supplement at any dose at 12 weeks but not at 24 weeks.6 However, the study authors noted that publication bias couldn't be determined and that many of the trials were small and used unsatisfactory methods. Due to this, study authors concluded, "The evidence that Ginkgo has predictable and clinically significant benefit for people with dementia or cognitive impairment is inconsistent and unconvincing."

Findings also are mixed for adults with normal cognitive functioning. A study of 188 adults aged 45–56 with normal cognitive function randomized to receive 240 mg of ginkgo extract once daily or placebo for six weeks found those receiving the ginkgo supplement had improved memory recall but not recognition. While this one study might suggest the potential for short-term benefits of ginkgo supplementation in middle-aged adults with normal cognitive function, earlier studies in healthy individuals didn't demonstrate a significant benefit to memory.7

Safety
While it appears from human studies that moderate doses of ginkgo extract are safe, the NTP studied the effects of an oral ginkgo extract in rats and mice at a dose several hundred times more per kg of body weight than what's taken by humans. It found an increase in liver cancer in male and female mice and an increase in cancer of the thyroid gland in male and female rats and male mice over a two-year period. The NTP deemed more information is needed to determine any potential risks to humans, including identifying components in the extract accounting for the cancer incidence and collecting additional information on human intake of ginkgo extract.8

What's Really in the Supplements?
According to ConsumerLab.com, ginkgo supplements can be expensive to manufacture because it takes about 50 lbs of dried ginkgo leaves to make 1 lb of ginkgo extract. The result is a high rate of adulteration via spiking ginkgo supplements with compounds from other plants to make lower-quality extracts appear higher quality to consumers. Ginkgo extract contains two types of phytochemicals—flavanol glycosides and terpene lactones—contributing to antioxidant and blood vessel dilation benefits, respectively. According to ConsumerLab.com, one way manufacturers adulterate ginkgo is by purposefully using (or unknowingly purchasing raw materials with) more flavanol glycosides and little actual ginkgo.2

To test what's really in ginkgo supplements, in 2018 ConsumerLab.com performed quality tests on 13 popular brands of Ginkgo biloba supplements sold in the United States.2 Seven supplements contained the labeled amount of real ginkgo extract, and one product contained only 3% of the labeled amount of ginkgo extract. The tests also identified significant differences in cost of the supplement, ranging from nine cents to over $2 for an equivalent amount of ginkgo extract. Among the supplements tested, the following were "approved" by ConsumerLab.com for their quality and label accuracy, and for containing the same quantity of pure ginkgo extract as the labeled dose:

  • GNC Herbal Plus Ginkgo Biloba 120 mg;
  • Life Extension Ginkgo Biloba;
  • Nature Made Ginkgo Biloba;
  • Nature's Way Ginkgold;
  • Nutrilite Memory Builder;
  • Pure Encapsulations Memory Pro; and
  • The Vitamin Shoppe Ginkgo Biloba Extract.

Four products weren't approved, including BulkSupplements.com Ginkgo Biloba (for containing less than 3% of its labeled amount of ginkgo), Doctor's Best Extra Strength Ginkgo, ProCaps Laboratories Andrew Lessman Ginkgo Biloba 120, and Source Naturals Ginkgo-24 (for adulteration with an unknown botanical ingredient). Two products were labeled "uncertain" for potentially being adulterated: Metagenics GinkgoRose and NOW Double Strength Ginkgo Biloba 120 mg.

Based on these findings, ConsumerLab.com identified a Ginkgo biloba supplement "Top Pick" for consumers: Life Extension Ginkgo Biloba. According to ConsumerLab.com, this supplement contains the dose most commonly used in clinical trials (120 mg) while also containing the correct concentrations of flavanol glycosides and terpene lactones with no sign of adulteration. The cost also was less than the other supplements at just nine cents per capsule.2

Recommendations for Clients
Ginkgo has been shown to interact with other drugs including blood-thinning drugs such as warfarin and aspirin as well as reduce the efficacy of antiseizure medication and responses to blood sugar-lowering medications in people with diabetes. Ginkgo extract also can lead to potentially serious complications for people who have had or are at risk of having a stroke and may interfere with fertilization and conception.2

Anyone considering taking a ginkgo supplement should consult his or her health care provider before beginning, and RDs should remind patients not to take supplements in place of, or in combination with, prescription medication without first notifying their health care provider.

According to ConsumerLab.com, most research studies have used a standardized ginkgo extract containing 24% flavonol glycosides and 6% terpene lactones, so consumers should look for this on supplement labels that have been tested by independent third parties.2 Clients should be encouraged to compare label information for different brands of supplements using the Dietary Supplement Label Database to search for specific ingredients in a product, a particular supplement manufacturer, label text, and health-related claims.

RDs should remind patients and clients that "natural" and "safe" aren't synonymous, and, in the case of supplements, the terms "standardized," "verified," or "certified" on the bottle don't guarantee product quality or consistency. As it's difficult to determine the quality of a dietary supplement based on its label, there are a few independent organizations offering seals of approval indicating that the product has passed certain quality tests for factors such as potency and contamination. Importantly, any seal of approval doesn't mean the product is safe or effective, only that it was properly manufactured and contains the ingredients listed on the label without harmful levels of contaminants. Consumers can look for the ConsumerLab.com Approved Quality Product Seal,9 NSF certification seal,10 or US Pharmacopeial Convention supplement seal.11

— Jessica Levings, MS, RD, realtor, is a freelance writer and food industry consultant. She blogs at Home in on Health to provide consumers with accurate, science-based nutrition information and resources. You can read more of her articles at BalancedPantry.com and follow her on Twitter and Facebook @BalancedPantry.

References
1. Ginkgo. National Center for Complementary and Integrative Health website. https://nccih.nih.gov/health/ginkgo/ataglance.htm. Updated March 10, 2017.

2. Product review: Ginkgo biloba supplements review. ConsumerLab.com website. https://www.consumerlab.com/reviews/Ginkgo_Supplements_Memory_Review/GinkgoBiloba/. Updated March 19, 2018.

3. DeKosky S, Williamson J, Fitzpatrick A, et al. Ginkgo biloba for prevention of dementia: a randomized controlled trial. JAMA. 2008;300(19):2253-2262.

4. Le Bars P, Katz M, Berman N, et al. A placebo-controlled, double-blind, randomized trial of an extract of Ginkgo biloba for dementia. North American EGb Study Group. JAMA. 1997;278(16):1327-1332.

5. Kanowski S, Herrmann M, Stephan K, et al. Proof of efficacy of the ginkgo biloba special extract EGb 761 in outpatients suffering from mild to moderate primary degenerative dementia of the Alzheimer type or multi-infarct dementia. Pharmacopsychiatry. 1996;29(2):47-56.

6. Birks J, Grimley Evans J. Ginkgo biloba for cognitive impairment and dementia. Cochrane Database Syst Rev. 2007;(2):CD003120.

7. Laws KR, Sweetnam H, Kondel TK. Is Ginkgo biloba a cognitive enhancer in healthy individuals? A meta-analysis. Hum Psychopharmacol. 2012;27(6):527-533.

8. National Toxicology Program. NTP Technical Report on the toxicology and carcinogenesis studies of Ginkgo biloba extract (CAS No. 90045-36-6) in F344/N rats and B6C3F1/N mice (Gavage Studies). https://ntp.niehs.nih.gov/ntp/htdocs/lt_rpts/tr578_508.pdf. Published March 2013.

9. How to read a ConsumerLab.com Approved Quality Product Seal. ConsumerLab.com website. https://www.consumerlab.com/seal.asp

10. Product and ingredient certification. NSF website. http://www.nsf.org/services/by-industry/nutritional-products/dietary-supplements-testing

11. Dietary Supplements Verification Program. The United States Pharmacopeial Convention website. http://www.usp.org/verification-services/dietary-supplements-verification-program

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