APOE and dementia: Observational studies have also suggested a moderating effect of APOE status on the relationship between physical activity and risk of dementia, beta-amyloid status, gray and white matter volume, and cerebral blood flow, with some studies showing benefit for APOE-ε4 carriers (Kivipelto et al., 2008; Head et al., 2012; Brown et al., 2013; Smith et al., 2014; Zlatar et al., 2014) and others for APOE-ε4 non-carriers (Rovio et al., 2007; Kulmala et al., 2014; Luck et al., 2014).