LEP and early-onset autosomal dominant Alzheimer disease: Moreover, although higher leptin in mid-life might protect against Alzheimer's Disease in late-life,13 leptin levels heightened by obesity were negatively linked to brain volume in 517 individuals at the time of measurement14–which is consistent with leptin's role as proinflammatory cytokine15 that can enter the brain and modulate neuroinflammatory responses.16