The possible mechanisms by which 1,25(OH)(2)D(3) acts on the brain might include Ca(2+) signaling, buffering antioxidant, and anti-inflammatory defenses against vascular injury, stimulating neurotrophins and improving metabolic and cardiovascular function. In conclusion, we suggest that 1,25(OH)(2)D(3) might influence personality traits, promoting extrovert and open behavior.

Background: Alterations of the hypothalamic-pituitary-thyroid system at the hypophyseal level have been described in affective disorders. The NEO Five-Factor Inventory is a widely used instrument, which assesses neuroticism, a strong marker for vulnerability to depression. Methods: Endogenous serum concentrations of thyroid-stimulating hormone (TSH), free T3 and free T4 were measured and the NEO Five-Factor Inventory was performed in 121 healthy unrelated volunteers (51 male, 70 female; median age: 23 years, range from 17 to 71). Results: The TSH serum concentrations showed a median of 1.35 mU/l with a range from 0.1 to 4.0. The free T3 serum concentrations were 5.2 ± 0.7 pmol/l (mean ± SD), and the free T4 concentrations 16.5 ± 2.4 pmol/l (mean ± SD). The power of 0.4 of the TSH serum concentration and the logarithm of the depression-related factor neuroticism had a bivariate normal distribution and were negatively correlated (r = –0.337, p = 0.0002). Conclusion: Low TSH levels in healthy humans might be linked to an increased risk to develop depression.