BDNF and Alzheimer disease: These contradictory results may be related to sample heterogeneity (age, gender, education, condition, comorbidity, and medication) and methodological differences (cognitive rating tools and diagnostic criteria, sample type, blood processing, storage duration, etc.)(Balietti et al., 2018); for instance, blood BDNF decreased with age or weight in elderly individuals (Glud et al., 2019), increased in the early AD stage and decreased in the late stage (Laske et al., 2006).