BDNF is a factor in nerve growth and maturation, and is essential in synapse formation and plasticity. A lack of of it is implicated in psychiatric disorders such as schizophrenia, intellectual disability, autism and depression. Interestingly, it has been shown that unless there is sufficient BDNF in the brain, conventional antidepressants do not work very well, and when BDNF is infused directly into the brains of rodents, it produces an antidepressant effect.
It has also been shown that BDNF has a seasonal variation in concentration correlating with the amount of ambient sun; it increases in the spring and summer and decreases in fall and winter.  The authors of this research described the importance of their findings thusly: “This finding is important for our understanding of those factors regulating BDNF expression and may provide novel avenues to understand seasonal dependent changes in behavior and illness such as depression.”
BDNF has been shown to increase significantly after bright light exposure, and in what we would consider to be a remarkably important study, both light exposure and treadmill exercise increased its expression of
in rats, or as the researchers showed, exercise and/or bright light promoted neurogenesis (new nerve cell growth) in the adult rat brain. How important is this finding for adults who are worried about cognitive decline? We are actually seeing an example of new brain cells being built by bright light and exercise. What a wonderful way to help prevent Alzheimer’s disease and maintain mental sharpness into old age! Don’t forget your (safe) sunlight!
 Björkholma C, Monteggiab, L. BDNF — a key transducer of antidepressant effects. Neuropharmacology. 2016 March ; 102: 72–79.
 Siuciak JA, Lewis DR, Wiegand SJ, Lindsay RM. Antidepressant-like effect of brain-derived neurotrophic factor (BDNF). Pharmacol. Biochem. Behav. 1997; 56(1):131–137.
 Molendijk ML, Haffmans JP, Bus BA, Spinhoven P, Penninx BW, Prickaerts J, Oude Voshaar RC, Elzinga BM. Serum BDNF concentrations show strong seasonal variation and correlations with the amount of ambient sun. PLoS One. 2012;7(11):e48046.
 Tirassa P1, Iannitelli A, Sornelli F, Cirulli F, Mazza M, Calza A, Alleva E, Branchi I, Aloe L, Bersani G, Pacitti F. Daily serum and salivary BDNF levels correlate with morning-evening personality type in women and are affected by light therapy. Riv Psichiatr. 2012 Nov-Dec;47(6):527-34.
 Kwon SJ, Park J, Park SY, Song KS, Jung ST, Jung SB, Park IR, Choi WS, Kwon SO. Low-intensity treadmill exercise and/or bright light promote neurogenesis in adult rat brain. Neural Regen Res. 2013 Apr 5;8(10):922-9.