Diurnal variation and gender differences of plasma brain-derived neurotrophic factor in healthy human subjects

Diurnal changes of brain-derived neurotrophic factor (BDNF) mRNA and protein contents have been demonstrated in the rat central nervous system. In humans, however, insufficient data are available on diurnal variation of BDNF. We investigated plasma and serum BDNF levels at three different times of the day (9 a.m., 1 p.m. and 5 p.m.) in 18 healthy men and 18 healthy women. BDNF levels were assessed using an enzyme-linked immunosorbent assay (ELISA). We detected significant diurnal variation in plasma BDNF level in men, with a constant decrease throughout the day. However, we could not find diurnal variation in either the plasma BDNF of women or the serum BDNF in both men and women. When performing analysis of covariance with the age and body mass index as covariates, we found no significant differences of plasma and serum BDNF levels of the two sexes at the three time points. In psychiatric studies of blood BDNF level, diurnal variation in plasma BDNF level should be considered with respect to gender differences.