BDNF and neurodegenerative disease: Second, individuals with low BMI may reflect nutritional deficiencies that aggravate neurodegeneration, such as low vitamin B levels with the secondary elevation of homocysteine levels (Coin et al., 2012), or have low levels of important brain trophic factors (e.g., brain-derived neurotrophic factor) that deteriorate the development of neurodegenerative disease (Zuccato and Cattaneo, 2009).