While leafing through a bodybuilding magazine in the library, I noticed a small item concerning the effects of the popular herbal supplement, ginkgo biloba extract (GBE) on testosterone levels. For those who aren’t familiar with Ginkgo, the ginkgo tree, from which the extract is derived, is often referred to as a “living fossil” because it has been around since the days when dinosaurs walked around. Numerous studies show that elements found naturally in Ginkgo, such as various flavonoids, provide some beneficial health effects. For example, GBE is known to increase blood flow and is also a potent free radical inhibitor, meaning that it inhibits out-of-control oxidation in the body. Both of these qualities can boost brain power, and ginkgo’s main claim to fame is that it may help prevent the onset of dementia, and in other cases may increase brain function and alertness through an increased circulation effect. There are many other claims made for ginkgo, however. The item that I read in the bodybuilding magazine was taken from an abstract of a Chinese medical journal, and the study itself was published in Chinese. The study involved providing GBE to either normal or diabetic rats. Humans afflicted with type-2 diabetes often show low testosterone levels, and conversely, there are new studies linking the onset of both the metabolic syndrome and diabetes to low testosterone levels. The connection is that low testosterone levels promote an increased level of visceral, or deep-lying abdominal fat stores. These particular fat stores, in turn, are associated with a greater incidence of cardiovascular disease and diabetes. Sure enough, the study with rats showed that the diabetic rodents were lower in enzymes related to testosterone synthesis in the body, as well as a lower volume of cells in the Leydig cells of the testes, where testosterone is synthesized. But when diabetic rats were provided GBE for 12 weeks, most of the negative effects on testosterone synthesis were reversed or blocked. The conclusion of the study was that GBE enhanced testosterone synthesis in type-2 diabetic rats. Based on this conclusion, whoever wrote the article in the bodybuilding magazine extrapolated this study to human usage, suggesting that bodybuilders use GBE to boost testosterone levels.
There are several problems with this suggestion. For one, humans aren’t rats, and what works in a rat doesn’t always also work in humans. In addition, these were diabetic rats, and we do know that human diabetics tend to have lower testosterone levels, but this doesn’t apply to those who don’t have diabetes. Had the author of the bodybuilding article scrolled down the Pub Med page where he or she probably found the Chinese rat study, they would have found an earlier study, published in 2005 that featured human subjects. The purpose of the prior human study was to determine if using ginkgo significantly altered levels of steroid hormones, including free testosterone,cortisol, DHEA, and others. The subjects ingested 240 milligrams a day of GBE for 14 days. Before ingesting the GBE, all subjects provided baseline hormone levels for comparison purposes. The results showed that the GBE had no effect on any steroid hormones, including testosterone. This study included six men and five women, but no rats. So while GBE may indeed raise testosterone levels in diabetic rats, the odds are good that it does not provide comparable effects in humans.
The take home message from this little episode is that you should be suspicious of those who directly extrapolate animal research to humans in definitive terms. While some animal studies do prove transferable to humans, many do not. When I write my articles that involve animal research, I always end by noting that future studies should determine if the effect shown in animals is applicable to humans. And that can only be done through studies with humans, and not just one study, either.
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