Relationship between the dexamethasone suppression test and the l-tryptophan/competing amino acids ratio in depression

Mood effects of the amino acids tryptophan and tyrosine

“…As many depressed patients with the melancholic or psychotic subtype would be expected to have experienced weight loss, any reduced plasma tryptophan level might, however, be secondary to weight loss following depression onset. A study by Anderson et al (12), involving 31 depressed patients who met DSM-III criteria for major depression with melancholia or psychosis, confirmed the findings of Maes et al (9), but also reported that, overall, only the female patients had significantly decreased plasma tryptophan concentrations -perhaps because of greater weight loss. Specifically, their analyses quantified that plasma tryptophan levels did not correlate significantly with absolute weight loss in the patients as a whole (r = )0.15) or in male patients (r = 0.14), but that there was a significant negative correlation with weight loss in female patients (r = 0.64).…”

“…In their study, Maes et al (9) reported that the total plasma tryptophan and the tryptophan ⁄ branch-chain amino acid ratio (with both being indicators of the availability of tryptophan to the brain) were significantly decreased in patients meeting DSM-III criteria for major depression with melancholia or psychosis, but not for those with non-melancholic depression. Cowen et al (10) studied 12 patients who met DSM-III criteria for major depression with melancholia and 12 controls and quantified that total plasma tryptophan levels were decreased (by about 25%) and that the ratio of total tryptophan to neutral amino acids was also decreased in the patient set.…”

A Multivariate Analysis of Red Blood Cell Membrane Transports and Plasma Levels of <i>L</i>-Tyrosine and <i>L</i>-Tryptophan in Depressed Patients before Treatment and after Clinical Improvement

“…Earlier studies about plasma TYR, PHE and TRP have so far yielded inconsistent findings [Niskanen et al, 1975;de Myer et al, 1981;Joseph et al, 1984;Möller et al, 1985;Maes et al, 1987;Bovier et al, 1988;Mathis et al, 1988]. But some authors point out the possible role of membrane transport phenomena as regulatory activity in general homeostasis processes by establishment of flows in direction just as in magnitude [Christensen, 1986].…”

“…It must also be acknowledged that many previous investigations con cerning plasma levels of different amino acids in the field of depression have until now yielded inconsistent findings [Niskanen et al, 1976;De Myer et al. 1981;Möller et al, 1985;Maes et al, 1987], However, this question should be carefully formulated in a context of complexity each parameter 'per se' gets intrinsic proper ties but is also integrated in a functional system which confers on its 'elementary' properties. It is difficult to delete such an essential process.…”

A review of lifestyle factors that contribute to important pathways associated with major depression: Diet, sleep and exercise

“…Other investigations on the relationship between nutrients and depression have demonstrated a role of folate (Farah, 2009, Gilbody et al, 2007, Morris et al, 2008, tryptophan (Cowen et al, 1989, DeMyer et al, 1981, Maes et al, 1987, zinc (Cope and Levenson, 2010, Szewczyk et al, 2011, iron (Maes et al, 1996, Stewart and Hirani, 2012, Vahdat Shariatpanaahi et al, 2007, Yi et al, 2011, CoQ10 (Maes et al, 2009b), vitamin B6 (Merete et al, 2008, Moorthy et al, 2012, Skarupski et al, 2010, Williams et al, 2005, vitamin B12 (Hintikka et al, 2003, Moorthy et al, 2012, and selenium (Gao et al, 2012, Mokhber et al, 2011, Pasco et al, 2012. However, findings on most of these nutrients require further investigation before definitive conclusions about their relationship with depression can be made.…”