What it is
Mitochondrial dysfunction is the progressive decline in how well mitochondria — the cell's energy-producing organelles — generate ATP and manage by-products, which tends to increase with age.
Why it matters for longevity
It is one of the hallmarks of aging, linked to fatigue, metabolic disease and reduced resilience. Because mitochondria depend on NAD+, strategies that support NAD+ or mitochondrial quality (exercise, certain supplements, photobiomodulation) are of interest.
What the evidence shows
The mechanistic and animal evidence is strong, but it is one interacting hallmark among many. Consumer claims to “boost mitochondria” for longevity usually rest on biomarker or animal data, not human lifespan outcomes.
Bottom line
A genuine and central ageing mechanism — useful for understanding why interventions might work, but not a validated standalone target you can simply “fix”.