Sleep quality strongly affects memory, learning, mood, and neurodegeneration risk. Poor sleep is linked to cognitive decline, Alzheimer's disease, and depression.

Dysregulated diurnal cortisol rhythm disrupts stress response, hippocampal health, and mood regulation. Linked to anxiety, depression, and cognitive decline.

HRV reflects autonomic balance. Higher HRV indicates better stress resilience and cognitive flexibility; lower HRV increases risk of anxiety, depression, and neurodegeneration.

High RHR is linked to sympathetic overdrive; strongly associated with cardiovascular, cognitive, and mood outcomes. Easy-to-measure marker of systemic and nervous system health.

Proxy for processing speed and executive function. Slower reaction times predict cognitive decline, fall risk, and neurological disease progression.

Essential amino acid; precursor of serotonin and melatonin. Low tryptophan impairs mood, sleep, and cognitive function.

Even low-level lead exposure damages cognition, IQ, and mood. Neurotoxic effects are cumulative and long-lasting.

Neurotoxin affecting motor, cognitive, and mood domains. Higher risk with chronic exposure (e.g., fish, environment).

Reflects integration of sensory and motor control; useful for aging and fall risk.