University of Groningen Serum BDNF Concentrations Show Strong Seasonal Variation and Correlations with the Amount of Ambient Sunlight Molendijk,

Earlier findings show seasonality in processes and behaviors such as brain plasticity and depression that in part are regulated by Brain-Derived Neurotrophic Factor (BDNF). Based on this we investigated seasonal variation in serum BDNF concentrations in 2,851 persons who took part in the Netherlands Study of Depression and Anxiety (NESDA). Analyses by month of sampling (monthly n’s .196) showed pronounced seasonal variation in serum BDNF concentrations (P,.0001) with increasing concentrations in the spring-summer period (standardized regression weight (ß) = 0.19, P,. 0001) and decreasing concentrations in the autumn-winter period (ß = 20.17, P,.0001). Effect sizes [Cohen’s d] ranged from 0.27 to 0.66 for monthly significant differences. We found similar seasonal variation for both sexes and for persons with a DSM-IV depression diagnosis and healthy control subjects. In explorative analyses we found that the number of sunshine hours (a major trigger to entrain seasonality) in the week of blood withdrawal and the 10 weeks prior to this event positively correlated with serum BDNF concentrations (Pearson’s correlation coefficients ranged: 0.05 – 0.18) and this could partly explain the observed monthly variation. These results provide strong evidence that serum BDNF concentrations systematically vary over the year. This finding is important for our understanding of those factors that regulate BDNF expression and may provide novel avenues to understand seasonal dependent changes in behavior and illness such as depression. Finally, the findings reported here should be taken into account when designing and interpreting studies on BDNF. Citation: Molendijk ML, Haffmans JPM, Bus BAA, Spinhoven P, Penninx BWJH, et al. (2012) Serum BDNF Concentrations Show Strong Seasonal Variation and Correlations with the Amount of Ambient Sunlight. PLoS ONE 7(11): e48046. doi:10.1371/journal.pone. 0048046 Editor: Kenji Hashimoto, Chiba University Center for Forensic Mental Health, Japan Received September 4, 2012; Accepted September 20, 2012; Published November 2, 2012 Copyright: 2012 Molendijk et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: The Netherlands Study of Depression and Anxiety study infrastructure is financed by the Geestkracht program of ZonMW, the Dutch Scientific Organization-Medical Sciences (Grant no. 10.000.1002) and by complementary funding from participating mental healthcare institutions (GGZ Buitenamstel, GGZ Drenthe, GGZ Friesland, GGZ Geestgronden, GGZ Rivierduinen and Lentis) and Universities (Leiden University Medical Center, University Medical Center Groningen and VU University Medical Center). Brain-Derived Neurotrophic Factor measurements were financed with Netherlands Organisation for Scientific Research (NWO: Dutch Scientific Organization) VIDI-grant no. 016.085. 353 awarded to Dr. Elzinga. The contributions of Dr. Oude Voshaar and MD Bus were made possible by NWO Clinical Fellowship no. 907.0023. 1 awarded to Dr. Oude Voshaar. None of the authors report potential (financial) conflicts of interest. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have the following interest. Dr. Judith P.M. Haffmans is employed as a clinician by a semi-commercial company, the Parnassia-BAVO Group, the Hague, the Netherlands. There are no patents, products in development or marketed products to declare. This does not alter the authors’ adherence to all the PLOS ONE policies on sharing data and materials, as detailed online in the guide for authors. * E-mail: molendijkml@fsw.leidenuniv. nl