Depression and body mass index, a u-shaped association

Background Results of studies concerning the association between obesity and depression are conflicting. Some find a positive association, some a negative association and some find no association at all. Most studies, however, examine a linear association between Body Mass Index (BMI) and depression. The present study investigates if a nonlinear (U-shaped) trend is preferable over a linear trend to describe the relationship between BMI and depression, which means that both underweight and obesity are associated with depression. Methods We investigated the existence of such a U-curve in a sample of 43,534 individuals, aged between 18–90 years, who participated in a cross-sectional study (Continuous Survey of Living Conditions) of physical and mental health in the general population of the Netherlands. We calculated linear and nonlinear (quadratic) ANOVA with polynomial contrast and curve fit regression statistics to investigate whether there was a U-shaped trend in the association between BMI and depression. Results We find a very significant U-shaped association between BMI categories (underweight, normal, overweight and obesity) and depression (p ≤ 0.001). There is a trend indicating a significant difference in the association between males and females (p = 0.05). We find a very significant U-shaped (quadratic) association between BMI (BMI2) and depression (p ≤ 0.001), continuous BMI is not linearly associated with depression (p = 0.514). Conclusion The results of this study give evidence for a significant U-shaped trend in the association between BMI and depression

Bound Clusters and Pseudogap Transitions in Layered High-Tc Superconductors

This article is closed access.We show that negatively charged dopant ions in hole-doped, layered, high-Tc superconductors induce at low doping bound clusters of four holes in CuO layers. This phenomenon requires double degeneracy of the hole band provided by the anti-Jahn-Teller effect, where dopant ions push apical oxygen ions into their symmetry positions and release holes from Copper atoms. Experimentally, that is seen as nanoscale inhomogeneity in the pseudogap region. The broad pseudogap transition contains two separate transitions. We connect the higher temperature transition to unbinding of clustered holes out of the spin-singlet state in the CuO plane. The lower temperature transition removes directional stripy order of these dipolar clusters, and the bosonic, spin-zero band disappears. We report results on energetics of the cluster formation and fit the density parameter rs and dielectric constant to Hall measurements. Our model leads to the quantum critical point at doping 0.2 where bound clusters disappear at zero temperature