title: The putative effects of D-Aspartic acid on blood testosterone levels: A systematic review.
abstract: BACKGROUND
  D-Aspartic acid (D-Asp) is in invertebrate and vertebrate neuroendocrine tissues, where it carries out important physiological functions. Recently, it has been reported that D-Asp is involved in the synthesis and release of testosterone and is assumed can be used as a testosterone booster for infertile men, and by athletes to increase muscle mass and strength.
  
  
  OBJECTIVE
  The aim of this review is to summarize available evidence related to the effects of D-Asp on serum testosterone levels.
  
  
  METHODS
  We conducted a systematic review of all type studies, which evaluated the effect of the D-Asp on blood testosterone including published papers until October 2015, using PubMed, ISI Web of Science, ProQuest and Scopus database.
  
  
  RESULTS
  With 396 retrieved records, 23 animal studies and 4 human studies were included. In vivo and in vitro animal studies revealed the effect of D-Asp depending on species, sex and organ-specific. Our results showed that exogenous D-Asp enhances testosterone levels in male animal's studies, whereas studies in human yielded inconsistent results. The evidence for this association in man is still sparse, mostly because of limited number and poor quality studies.
  
  
  CONCLUSIONS
  There is an urgent need for more and well-designed human clinical trials with larger sample sizes and longer duration to investigate putative effects of D-Asp on testosterone concentrations.
authors.affiliation: Noncommunicable Diseases Research Center, Fasa University of Medical Sciences, Fasa, Iran.; Department of Clinical Nutrition, School of Nutrition and Food Sciences, Isfahan University of Medical Sciences, Isfahan, Iran.
authors.forename: Farzad
authors.initials: F
authors.lastname: Roshanzamir
authors.affiliation: Department of Clinical Nutrition, School of Nutrition and Food Sciences, Isfahan University of Medical Sciences, Isfahan, Iran.
authors.forename: Seyyed Morteza
authors.initials: SM
authors.lastname: Safavi
keywords: D-Aspartic acid; Systematic review; Testosterone