L-serine is a non-essential amino acid that proteinogenic amino acid and is known as a precursor of glycine, cysteine, phosphatidylserine, and sphingolipids. L-Serine is present in various foods, such as soybeans, as a protein component or free amino acid. The mean intakes of L-serine in Japanese were reported to be 3.81 g/day for males and 3.24 g/day for females (Kato et al., Jap. Soc. Nutri. Diet. 71 (2013)). In recent years, L- ornithine has been used as a supplement for physiological CNS functions (Shigemi et al., Neurosci Lett. 468 (2010)), sleeping quality (Ito et al., Springer Plus 456 (2014)), skin and so on..
The following reports on the safety of L-serine are available. In a non-clinical safety study, rats were exposed to repeated doses of L-serine at doses of 500, 1,500, and 3,000 mg/kg/ days for 13 weeks. The NOAEL for L-serine was reported as 3,000 mg/kg/ days (Kaneko et al., Food Chem Toxicol. 47 (2009)). In addition, rats were tested for toxicity by repeated administration of L-serine at doses of 0.06, 0.5, 1.5, and 5.0% in the diet for 90 days. From the results of this study, the NOAEL for L-serine was reported to be 5.0% diet (male: 2,765 mg/kg/ days, female: 2,905 mg/kg/ days) (Tada et al., J Toxicol Pathol 23 (2010)). In human safety studies, but not in healthy adults, 20 patients with amyotrophic lateral sclerosis (ALS) were tested for 6 months at doses of 0.5, 2.5, 7.5, and 15 g/day of L-serine. The results of this study indicate that no adverse events were observed at doses up to 15 g/day of L-serine (Levine et al., Amyotrophic Lateral Sclerosis and Frontotemporal Degeneration. 18 (2017)).


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