Threonine Introduction

Threonine is an essential amino acid that cannot be synthesized for use in mammalian tissues. Because of this, a dietary supply of threonine must be achieved on a daily basis to regulate and maintain proper protein balance within the body. Threonine is an important component of many proteins found in the human body and is needed for the formation of such protein rich tissues as collagen, elastin, and tooth enamel. [1] The heart, central nervous system, and skeletal muscle provide the highest concentrations of this essential amino acid.

A precursor to glycine and serine, threonine also provides the body with a mild glucose sparing effect, assisting in the stabilization of blood sugars via gluconeogenesis in the liver. Nutrients consumed by diet are more readily absorbed when threonine is present, aiding in both its metabolism and assimilation. Threonine may also prove therapeutic when combined with the branched-chain amino acids valine, isoleucine, and leucine.

Adequate levels of threonine are found in the majority of meats, dairy foods, and eggs. Moderate to lower levels are found in nuts, beans, seeds, wheat germ, and vegetables. Grains provide little or no value in achieving proper daily intake of this amino acid, and dietary intake must be adjusted accordingly. Serving sizes below are based upon 100 grams of a given food source and are expressed in milligrams, representing the amount of threonine contained.

[2]

The dietary supplementation of threonine can be useful in diverse conditions that develop as the consequence of both neurological and physical impairment. In the brain, threonine is elemental in the growth and activity of the thymus gland, production of neurotransmitters, and overall health of the nervous system.

Nervous system response and diseases such as Lou Gehrig’s disease may be improved by supplemental dosages of threonine. [3] Prolonged dietary supplementation of this essential amino acid may also benefit persons suffering from multiple sclerosis, and depression. [4, 5] Dosages of one gram of threonine twice daily have shown marked improvement in individuals suffering from clinical depression.

Immunological response may be directly affected by proper intake of threonine as well. In conjunction with the amino acids alanine, aspartic acid, cysteine, and lysine, threonine stimulated the immune system by aiding in the production of antibodies. [6] This may prove extremely important as threonine levels decrease with age, and increase when persons are faced with stressors, or severe trauma.

Threonine is also important in liver health. When combined with aspartic acid and methionine, threonine aids in the general functioning of the liver. It has been suggested that in times of choline deficiencies, threonine plays a minor role as a lipotropic in controlling fat accumulation in the liver, i.e. “fatty liver.” [7] Clinical studies continue on threonine’s potential to inhibit the accumulation of fat in other vital organs.

Other areas of interest include burn or trauma victims. Patients suffering form these conditions usually exhibit greater urinary spills of threonine. A variety of research indicates that an increased intake of threonine during these stressful periods may aid in the recovery process. Therapeutic dosages range from 300 to 1,200 milligrams per day.

The Recommended Daily Allowance (RDA) of threonine has been established as the minimal amount required per day to ward of deficiencies of this nutrient:

[8]

Additionally, the U.S. National Academy of Sciences recommends that healthy people achieve .36 grams of highly bioavailable protein for each pound of bodyweight - equaling 0.8 grams of protein, per kilogram of bodyweight.

Threonine Toxicities

Toxicities of this essential amino acid are rare and research is scarce. Side effects resulting from prolonged, excessive intakes of threonine may include hypertension (increased blood pressure) in adults. [9]

Threonine Deficiencies

Inadequate intake of threonine may result in irritability and generalized personality disorders. Prolonged deficiencies may be associated with a weakened cellular response and inhibited antibody formation.

Vegetarians are at greatest risk for the development of a deficiency, due to the low threonine content in vegetables and grains. Supplementation of L-threonine is recommended in these individuals.

1. Balch, Phyllis A., James F. “Amino Acids.” Prescription for Nutritional Healing. Ed. Amy C. Tecklenberg. New York, NY: Penguin Putnam Inc., 3rd Ed. 2000. 42-53.

2. Nutrition Data. “999 Foods; Highest in Threonine.” (2004)

http://www.nutritiondata.com/foods-000080000000000000000-w1.html

3. Blin O, et al. A Double-Blind Placebo Controlled Trial of L Threonine in Amyotrophic Lateral Sclerosis. La Presse Medicale. Sep1989;18(30):1469-70.

4. Doolittle TH, Hauser SL, et al. Antispasticity Effect of Threonine in Multiple Sclerosis. Archives of Neurology. Sep1992;49:923-26.

5. Maes M, et al. Serum Levels of Excitatory Amino Acids, Serine, Glycine, Histidine, Threonine, Taurine, Alanine and Arginine in Treatment-resistant Depression: Modulation by Treatment with Antidepressants and Prediction of Clinical Responsivity. Acta Psychiatr Scand. Apr1998;97(4):302-08.

6. Lotan R, et al. The Effect of Lysine and Threonine Supplementation on the Immune Response of Growing Rats Fed Wheat Gluten Diets. Nutr Teports Inter. 1980;22(3):313-18.

7. Fukuda N, Hidaka T, Toda T, Sugano M. Altered hepatic metabolism of free fatty acid in rats fed a threonine-imbalanced diet. J Nutr Sci Vitaminol (Tokyo). Oct1990;36(5):467-74.

8. Zest for life information page. “RDA of amino acids.” (1999-2003) http://www.anyvitamins.com/amino-acids/rda-amino-acids.htm (14 Sept. 2004).

9. Vasdev S, Whalen M, et al. Ethanol- and Threonine-induced Hypertension in Rats: A Common Mechanism. Can J Cardiol. Oct1995;11(9):807-15.