Safety of Amino Acids

Safety Studies of Amino Acids in Animals

Indispensable Amino Acids
Amino Acid		Animal	Method of administration	Duration (recovery period)	Dose	Reference
	L-histidine	Fischer rat	Mixed food	13W	0.31, 0.62, 1.25, 2.5, 5% (w/w)	[Japanese] Ikezaki S, Nishikawa A, et al. "13-week subchronic toxicity study of L-histidine monohydrochloride in F344 rats" Bull Natl Ins Health Sci (1994), 112:57-63
	L-isoleucine	SD rat	Mixed food	13W (5W)	1.25, 2.5, 5% (w/w)	Tsubuku S, Hatayama K, et al. “Thirteen-week oral toxicity study of branched-chain amino acids in rats” Int J Toxicol (2004), 23(2):119-126
	L-leucine	SD rat	Mixed food	13W (5W)	1.25, 2.5, 5% (w/w)	Tsubuku S, Hatayama K, et al. “Thirteen-week oral toxicity study of branched-chain amino acids in rats” Int J Toxicol (2004), 23(2):119-126
	L-lysine/HCl	SD rat	Mixed food	13W (5W)	1.25, 2.5, 5% (w/w)	Tsubuku S, Mochizuki M, et al. “Thirteen-week oral toxicity study of L-lysine hydrochloride in rats” Int J Toxicol (2004), 23(2):113-118
	L-methionine	Fischer rat ♂	Mixed food	4W	0.1, 0.3, 0.9, 2.7% (w/w)	Chin K, Toue S, et al. "A 4-week toxicity study of methionine in male rats" Int J Toxicol (2015), 34(3):233-241
	L-phenylalanine	SD rat	Mixed food	28 days	0.5, 1.5, 5.0%	Shibui Y, Miwa T, et al. "28-Day dietary toxicity study of L-phenylalanine in rats" Fund Toxicol Sci (2014), 1(2):29-38
	L-threonine	SD rat	Mixed food	13W (5W)	1.25, 2.5, 5.0%	Aoki M, Ishida S, et al. "A 13-week feeding toxicity study of L-threonine in rats with a recovery period of 5 weeks" Fund Toxicol Sci (2014), 1(2):49-62
	L-tryptophan	SD rat	Mixed food	13W (5W)	1.25, 2.5, 5.0%	Shibui Y, Matsumoto H, et al. +LOAEL(mg/kg/day) was calicurated using original research data (BW for LOAEL). "Thirteen week toxicity study of dietary L‐tryptophan in rats with a recovery period of 5 weeks" J Appl Toxicol (2018), 38(4): 552-563
	L-valine	SD rat	Mixed food	13W (5W)	1.25, 2.5, 5% (w/w)	Tsubuku S, Hatayama K, et al. “Thirteen-week oral toxicity study of branched-chain amino acids in rats” Int J Toxicol (2004), 23(2):119-126
Dispensable Amino Acids
	L-alanine	SD rat	Gavage	4W (2W)	2,000mg/kg/day	Aoki M, Mochizuki M, et al. “A 4-week oral toxicity study of L-alanine in rats with a recovery period of 2 weeks” Fund Toxicol Sci (2014), 1(2):63-72
	L-arginine	SD rat	Mixed food	13W (5W)	1.25, 2.5, 5% (w/w)	Tsubuku S, Hatayama K, et al. “Thirteen-week oral toxicity study of L-arginine in rats” Int J Toxicol (2004), 23(2):101-105
		Pig	Mixed food twice a day	13W	1.21, 1.81, 2.42% (w/w)	Hu S, Li X, et al. “Safety of long-term dietary supplementation with L-arginine in pigs” Amino Acids (2015), 47(5):925-936
		Pig	Mixed food twice a day	13W	1.0, 1.5, 2.0% (w/w)
		SD rat	Drinking water	13W	2.18, 4.35 g/kg/day	Yang Y, Wu Z, et al. “Safety of long‑term dietary supplementation with L‑arginine in rats” Amino Acids (2015), 47(9):1909-1920
	L-asparagine	Fischer rat	Mixed food	90 days	1.25, 2.5, 5% (w/w)	Yokohira M, Hosokawa K, et al. "A 90-day toxicity study of L-asparagine, a food additive, in F344 rats" Food Chem Toxicol (2008), 46(7):2568-2572
	L-aspartic acid	Fischer rat	Mixed food	90 days	0.05, 1.25, 2.5, 5.0% (w/w)	Tada Y, Yano N, et al. "Toxic effects of L-aspartic acid at high dose levels on kidneys and salivary glands in Fischer 344 rats detected in a 90-day feeding study" Food Chem Toxicol (2008), 46(8):2789-2795
	L-cysteine	SD rat	Gavage	4W	500, 1000, 2000 mg/kg/day	Shibui Y, Sakai R, et al. "Comparisons of L-cysteine and D-cysteine toxicity in 4-week repeated-dose toxicity studies of rats receiving daily oral administration" J Toxicol Pathol (2017), 30(3):217-229
	L-glutamate	-	-	-	-	Acceptable daily intake (ADI) is not specified in JECFA report. ADI can be driven from NOAEL, so that NOAEL of L-Glu/Na is not also specified.: Principles for the safety assessment of food additives and contaminants in food. World Health Organization International Program on Chemical Safety in Cooperation with the Joint FAO/WHO Expert Committee on Food Additives, Geneva, Environmental Health Criteria 70 (1987).
	L-glutamate	CD-1 mouse	Mixed food	3-genaration reproductive toxicity: F0：Gestation & lactation F1: Postweaning – Lactation F2: Postweaning – Lactation F3: Birth - Weaning	1.0, 4.0% (w/w)	Anantharaman K “In utero and dietary administration of monosodium L-glutamate to mice: Reproductive performance and development in a multigeneration study” Glutamic Acid: Advances in Biochemistry and Physiology, ed. by Filer LJ, et al., Raven Press, NY (1979):231-253
	L-glutamine	SD rat	Mixed food	13W (5W)	1.25, 2.5, 5% (w/w)	Tsubuku S, Hatayama K, et al. “Thirteen-week oral toxicity study of L-glutamine in rats.” Int J Toxicol (2004), 23(2):107-112
	L-glycine	SD rat	Gavage	28 days	500, 1000, 2000 mg/kg/day	Shibui Y, Miwa T, et al. "A 4-week repeated dose toxicity study of glycine in rats by gavage administration" J Toxicol Pathol (2013), 26(4) 405–412, 2013
	L-proline	Fischer rat	Mixed food	90 days	0.625, 1.25, 2.5, 5.0%	Tada Y, Yano N, et al. "Toxicological evaluation of L-proline in a 90-day feeding study with Fischer 344 rats" Regul Toxicol Pharmacol (2010), 58(1):114-120
	L-serine	SD rat	Gavage	13W	500, 1500, 3000 mg/kg/day	Kaneko I, Han L, et al. "A 13-week subchronic oral toxicity study of L-serine in rats" Food Chem Toxicol (2009), 47(9):2356-2360
	L-serine	Fischer rat	Mixed food	90 days	0.06, 0.5, 1.5, 5.0%	Tada Y, Yano N, et al. "A 90-day feeding toxicity study of L-serine in male and female Fischer 344 rats" J Toxicol Pathol (2010), 23(1):39-47
	L-tyrosine	SD rat	Gavage	13W	200, 600, 2000 mg/kg/day	Shibui Y, Manabe Y, et al. "13-week repeated dose toxicity study of l-tyrosine in rats by daily oral administration" Food Chem Toxicol (2016), 87:55-64
Non-code protein Amino Acids
	L-ornithine	SD rat	Mixed food	13W (5W)	1.25, 2.5, 5.0%	Ishida S, Sarada M, et al. "Genotoxicity and subchronic oral toxicity of L-ornithine monohydrochloride" Regul Toxicol Pharmacol (2013), 67(3):360-71
	L-citrulline	SD rat	Gavage	4W	2000 mg/kg/day	Morita M, Yamaguchi T, et al. "A 4-week oral gavage toxicity study of L-citrulline in rats" Fund Toxicol Sci (2017), 4(5):219-227
	L-hydroxyproline	SD rat	Gavage	28 days (14 days)	40, 200, 1000, 4000 mg/kg/day	Akiduki S, Kawada Y, et al. “Twenty-eight-day oral toxicity study of L-hydroxyproline in rats with 14-day post-treatment observation period” Fund Toxicol Sci (2019), 6(3):65-74

Safety Studies of Amino Acids in Human

Review
Amino Acid		Category	Subject	Method of administration	Duration	Dose	Reference
	Amino acids	Safety Review	-	-	-	-	Elango R. Tolerable Upper Intake Level for Individual Amino Acids in Humans: A Narrative Review of Recent Clinical Studies Advances in Nutrition (2023), 14(4): 885-894.
	Amino acids	Safety Review	-	-	-	-	Blachier F, et al. Tolerable amounts of amino acids for human supplementation: summary and lessons from published peer-reviewed studies Amino Acids (2021) 53(9):1313-1328
Indispensable Amino Acids
	L-histidine	Safety Assessment Study	Healthy adults (male and female)	Oral	4W	4, 8, 12, 16 g/day	Gheller ME, et al. Tolerance to graded dosages of histidine supplementation in healthy human adults American Journal of Clinical Nutrition (2020), 112(5): 1358-1367.
		Safety Review	-	-	-	-	Thalacker-Mercer AE, et al. Benefits and Adverse Effects of Histidine Supplementation The Journal of Nutrition (2020), 150(Suppl1), 2588S-2592S.
		Safety Review	-	-	-	-	Cynober L, et al. Proposals for Upper Limits of Safe Intake for Methionine, Histidine, and Lysine in Healthy Humans The Journal of Nutrition (2020)150(Suppl1):2606S-2608S,
	L-isoleucine
	L-leucine	Safety Assessment Study	Healthy adults (male)	Oral	Once	50, 150, 250, 500, 750, 1000, 1250 mg/kg/day	Elango R, et al. Determination of the tolerable upper intake level of leucine in acute dietary studies in young men American Journal of Clinical Nutrition (2012), 96(4):759-767.
		Safety Review	-	-	-	-	Cynober L, et al. Proposals for Upper Limits of Safe Intake for Arginine and Tryptophan in Young Adults and an Upper Limit of Safe Intake for Leucine in the Elderly The Journal of Nutrition (2016), 146(12):2652S-2654S.
		Safety Review	-	-	-	-	Pencharz PB, et al. Determination of the tolerable upper intake level of leucine in adult men The Journal of Nutrition (2012), 142(12):2220S-2224S.
	L-lysine/HCl	Safety Review	-	-	-	-	Hayamizu K, et al. Safety assessment of L-lysine oral intake: a systematic review Amino Acids (2019), 51(4):647-659.
	L-lysine/HCl	Safety Review	-	-	-	-	Cynober L, et al. Proposals for Upper Limits of Safe Intake for Methionine, Histidine, and Lysine in Healthy Humans The Journal of Nutrition (2020)150(Suppl1):2606S-2608S,
	L-methionine	Safety Assessment Study	Healthy older adults	Oral	4W	9.2, 22.5, 46.3, 91 mg/kg/day	Deutz NE, et al. Tolerance to increased supplemented dietary intakes of methionine in healthy older adults American Journal of Clinical Nutrition (2017) 106(2):675-683.
		Safety Review	-	-	-	-	Ligthart-Melis GC. et al. Metabolic Consequences of Supplemented Methionine in a Clinical Context The Journal of Nutrition (2020)150(Suppl1):2538S-2547S,
		Safety Review	-	-	-	-	Cynober L, et al. Proposals for Upper Limits of Safe Intake for Methionine, Histidine, and Lysine in Healthy Humans The Journal of Nutrition (2020)150(Suppl1):2606S-2608S,
		Case Study	Patients with coronary artery or peripheral arterial disease	Oral	Once	100 mg/kg	Krupkova-Meixnerova L, et al. Methionine-loading test: evaluation of adverse effects and safety in an epidemiological study Nutrition(2002), 21(2):151-156.
		Case Study	Healthy nonsmoking adults and patients with several thrombotic conditions.	Oral	Once	100 mg/kg	Majluf-Cruz A, et al. Safety of the oral methionine load test: effects on the clinical performance and laboratory tests Revista de Investigacion Clinica (2013), 65(4):323-330.
	L-phenylalanine	Safety Assessment Study	Healthy adults (male)	Oral	4W	3, 6, 9, 12 g/day	Miura N. et al. Subchronic Tolerance Trials of Graded Oral Supplementation with Phenylalanine or Serine in Healthy Adults Nutrients (2021) 13(6): 1976
		Safety Review	-	-	-	-	Blachier F, et al. Tolerable amounts of amino acids for human supplementation: summary and lessons from published peer-reviewed studies Amino Acids (2021) 53(9):1313-1328
		Case Study	Healthy, active male	Oral	Once	3g	Ueda K. et al. The effects of phenylalanine on exercise-induced fat oxidation: a preliminary, double-blind, placebo-controlled, crossover trial Journal of the International Society of Sports Nutrition (2017), 14:34.
	L-threonine	Case Study	Patients with familial spastic paraparesis (FSP)	Oral	2W	4.5, 6 g/day	Growdon J.H. et al. L-Threonine in the Treatment of Spasticity Clinical neuropharmacology (1991), 14(5):403-412.
		Case Study	Patients with spinal spasticity	Oral	-	6 g/day	Lee A. and Patterson V. A double-blind study of L-threonine in patients with spinal spasticity Acta Neurologica Scandinavica (1993), 88(5):334-338.
		Case Study	Patients with amyotrophic lateral sclerosis (ALS)	Oral	6M	4 g/day	Tandan R. et al. A controlled trial of amino acid therapy in amyotrophic lateral sclerosis Neurology (1996), 47(5):1220-1226.
	L-tryptophan	Safety Assessment Study	Healthy Japanese women	Oral	21D	1, 2, 3, 4, 5 g/day	Hiratsuka C, et al. Supplementing healthy women with up to 5.0 g/d of L-tryptophan has no adverse effects The Journal of Nutrition (2013), 143(6):859-866
	L-tryptophan	Safety Review	-	-	-	-	Cynober L, et al. Proposals for Upper Limits of Safe Intake for Arginine and Tryptophan in Young Adults and an Upper Limit of Safe Intake for Leucine in the Elderly The Journal of Nutrition (2016), 146(12): 2652S-2654S.
	L-valine
Dispensable Amino Acids
	L-alanine	Case Study	Therapeutically starved obese subjects	Oral	1D	50 g	Genuth SM. Effects of oral alanine administration in fasting obese subjects Metabolism. 22(7), 1973, 927-937.
	L-arginine	Safety Review	-	-	-	-	Cynober L, et al. Proposals for Upper Limits of Safe Intake for Arginine and Tryptophan in Young Adults and an Upper Limit of Safe Intake for Leucine in the Elderly The Journal of Nutrition (2016), 146(12): 2652S-2654S.
		Safety Review	-	-	-	-	Shao A, et al. Risk assessment for the amino acids taurine, L-glutamine and L-arginine Regulatory Toxicology and Pharmacology (2008), 50(3):376-399,
		Safety Assessment Study	Adults (male and female)	Oral	90D	0, 15, 30 g/day	McNeal CJ, et al. Safety of dietary supplementation with arginine in adult humans. Amino Acids (2018), 50(9):1215-1229.
	L-asparagine
	L-aspartic acid	Case Study	-	Oral	-	5, 10 g	Harold EC. et al. Stimulation of pituitary hormone secretion by neurotransmitter amino acids in humans. Metabolism. 38(12), 1989, 1179-1182.
	L-cysteine	Case Study	-	Oral	-	5, 10 g	Harold EC. et al. Stimulation of pituitary hormone secretion by neurotransmitter amino acids in humans. Metabolism. 38(12), 1989, 1179-1182.
	L-glutamate	Safety Review	-	-	-	-	Acceptable daily intake (ADI) is not specified in JECFA report. ADI can be driven from NOAEL, so that NOAEL of L-Glu/Na is not also specified.: Principles for the safety assessment of food additives and contaminants in food. World Health Organization
	L-glutamate	Safety Review	-	-	-	-	International Program on Chemical Safety in Cooperation with the Joint FAO/WHO Expert Committee on Food Additives, Geneva, Environmental Health Criteria 70 (1987).
	L-glutamine	Safety Assessment Study	Healthy adults (male), HIV patients with AIDS-associated weight loss and cancer patients with wasting	Oral	-	14 g	Rathmacher JA. et al. Supplementation with a combination of beta-hydroxy-beta-methylbutyrate (HMB), arginine, and glutamine is safe and could improve hematological parameters Journal of Parenteral and enteral nutrition (2004) 28(2):65-75.
		Safety Review	-	-	-	-	Shao A, et al. Risk assessment for the amino acids taurine, L-glutamine and L-arginine Regulatory Toxicology and Pharmacology (2008), 50(3):376-399,
		Case Study	Healthy adults (male)	Oral	1D	0.3, 0.6, 0.9 g/kg·FFM	Ogden HB, et al. Gastrointestinal Tolerance of Low, Medium and High Dose Acute Oral l-Glutamine Supplementation in Healthy Adults: A Pilot Study Nutrients (2020) 12(10):2953.
	Glycine	Safety Assessment Study	Healthy adults (male and female)	Oral	7D	9 g/day	Inagawa K, et al. Assessment of Acute Adverse Events of Glycine Ingestion at a High Dose in Human Volunteers Journal of Urban Living and Health Association (2006), 50(1):27-32.
	L-proline
	L-serine	Safety Assessment Study	Healthy adults (male)	Oral	4W	3, 6, 9, 12 g/day	Miura N. et al. Subchronic Tolerance Trials of Graded Oral Supplementation with Phenylalanine or Serine in Healthy Adults Nutrients (2021) 13(6): 1976
	L-serine	Safety Review	-	-	-	-	Blachier F, et al. Tolerable amounts of amino acids for human supplementation: summary and lessons from published peer-reviewed studies Amino Acids (2021) 53(9):1313-1328
	L-tyrosine	Case Study	Patients with essential hypertension	Oral	2W	7.5 g/day	Sole MJ. Et al. Chronic dietary tyrosine supplements do not affect mild essential hypertension Hypertension (1985), 7(4):593-596.
		Case Study	Subjects with narcolepsy and cataplexy	Oral	4W	9 g/day	Elwes RDC. et al. Treatment of narcolepsy with L-tyrosine: double-blind placebo-controlled trial The Lancet (1989), 334(8671):1067-1069.
		Case Study	-	Oral	1D	150 mg/day	Neri DF. et al. The effects of tyrosine on cognitive performance during extended wakefulness Aviation, Space and Environmental Medicine (1995), 66(4):313-319.
		Case Study	Patients with nemaline myopathy	Oral	-	250 to 3000 mg/day	Monique MR. et al. Dietary L-tyrosine supplementation in nemaline myopathy Journal of Child Neurology (2008),23(6):609-13.
Non-code protein Amino Acids
	L-ornithine/HCl	Safety Assessment Study	Healthy adults (male)	Oral	4W	3.2, 6, 9.2, 12 g/day	Miura N. et al. Subchronic tolerance trials of graded oral supplementation with ornithine hydrochloride or citrulline in healthy adults Amino Acid (2022); 1-13.
	L-ornithine/HCl	Case Study	Healthy adults (male and female)	Oral	-	2000 mg/day for 7D and 6000 mg/day for 1D	Sugino T. et al. L-ornithine supplementation attenuates physical fatigue in healthy volunteers by modulating lipid and amino acid metabolism Nutrition Research (2008), 28(11):738-743.
	L-citruline	Safety Assessment Study	Healthy adults (male)	Oral	4W	6, 12, 18, 24 g/day	Miura N. et al. Subchronic tolerance trials of graded oral supplementation with ornithine hydrochloride or citrulline in healthy adults Amino Acid (2022); 1-13.
	L-citruline	Case Study	Healthy adults (male)	Oral	1D	2, 5, 10, 15 g	Moinard C. et al. Dose-ranging effects of citrulline administration on plasma amino acids and hormonal patterns in healthy subjects: the Citrudose pharmacokinetic study British Journal of Nutrition (2008), 99(4):855-862.
	L-hydroxyproline