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D-aspartic acid can also help to reduce cortisol levels. Cortisol is known as the “stress” hormone because its production increases during stressful situations. High cortisol levels can have many negative side effects, such as weight gain, muscle tissue breakdown, or increased blood sugar. Taking a supplement that includes cortisol can reduce stress and prevent excess fat storage or muscle loss.
K. Aleisha Fetters, M.S., C.S.C.S., is a Chicago-based personal and online trainer. She has a graduate degree in health and science reporting from the Medill School of Journalism at Northwestern University and regularly contributes to Men's Health, Women's Health, USNews.com, TIME, and SHAPE. When she's not lifting something heavy, she's usually guzzling coffee and writing about the health benefits of doing so.
In regard to the blood brain barrier (BBB), which is a tightly woven mesh of non-fenestrated microcapillary endothelial cells (MCECs) that prevents passive diffusion of many water-soluble or large compounds into the brain, creatine can be taken into the brain via the SLC6A8 transporter. In contrast, the creatine precursor (guanidinoacetate, or GAA) only appears to enter this transporter during creatine deficiency. More creatine is taken up than effluxed, and more GAA is effluxed rather than taken up, suggesting that creatine utilization in the brain from blood-borne sources is the major source of neural creatine. However, “capable of passage” differs from “unregulated passage” and creatine appears to have tightly regulated entry into the brain in vivo. After injecting rats with a large dose of creatine, creatine levels increased and plateaued at 70uM above baseline levels. These baseline levels are about 10mM, so this equates to an 0.7% increase when superloaded. These kinetics may be a reason for the relative lack of neural effects of creatine supplementation in creatine sufficient populations.