To ensure that this reaction was not purely rodent-based, the researchers also checked blood from the elderly. The older men and women who usually went for exercise showed higher levels of GPLD1 in their bloodstream than those who did not.
The combined result of these results seems to be that exercise partially improves brain health by getting the liver to pump out extra amounts of GPLD1, says Dr. Mislead, although it is not yet clear how the protein then changes the brain. Subsequent experiments by the researchers showed that the protein probably does not break the blood-brain barrier and acts directly on the brain, says Dr. Villeda. Instead, it is likely to stimulate changes in other tissues and cells elsewhere in the body. These tissues in turn produce even more proteins that have effects on other tissues that eventually lead to direct changes in the neurotransmitters, genes and cells in the brain itself that undergo cognitive improvements.
This experiment mainly involved mice, but not humans, and says nothing about the systemic effects of extra GPLD1, which in high amounts may be undesirable. More fundamentally, the findings highlight the pervasive, complex, whole-body effects of exercise, with the liver, in this case, somehow changing the senses and brains after exercise. At present, it is impossible to know whether the same synchronized, interwoven processes would all occur in response to a GPLD1 training pill and, if not, whether it could be considered a training pill at all.
Dr. Villeda quickly agrees that pharmaceutical GPLD1, while effective for brain health, “would not recapitulate the benefits of exercise.” It would not be one of the usual fat burning, muscle building or cardiovascular improvements, he points out. But he hopes that if future experiments in his lab with animals and humans show consistent results, the substance may eventually help people who have difficulty moving better to think better.