Cellular Repair: Targeting the Biology of Aging at Its Source

Every cell in your body sustains tens of thousands of DNA lesions every single day — damage caused by normal metabolic processes, reactive oxygen species, environmental exposures, and replication errors. Multiple repair pathways exist to correct this damage, and they are remarkably efficient in youth. One of the most important of these pathways depends on PARP-1, an enzyme that requires NAD+ as a direct substrate to function. As NAD+ levels decline with age — falling approximately 40–60% between early adulthood and age 60 — PARP-1 activity decreases, and unrepaired DNA damage begins to accumulate. This relationship between NAD+ decline and impaired DNA repair is a well-documented mechanism of biological aging (Fang EF et al., Cell Metabolism, 2016).

Autophagy is the process by which cells identify, break down, and recycle damaged proteins, dysfunctional organelles, and intracellular debris. It is the primary quality-control mechanism within cells, and its importance to health and longevity was recognized with the 2016 Nobel Prize in Physiology or Medicine, awarded to Yoshinori Ohsumi for his foundational work on autophagy mechanisms.

The problem is that autophagy declines with age. As this self-cleaning process becomes less efficient, damaged mitochondria (a process specifically called mitophagy when applied to mitochondria), protein aggregates, and dysfunctional cellular components accumulate — contributing to inflammation, reduced energy production, and tissue dysfunction. The most evidence-supported activators of autophagy are not pharmacological agents but behavioral interventions: fasting, which activates autophagy by switching on AMPK and suppressing mTOR, and aerobic exercise, which potently stimulates mitophagy in skeletal muscle.

Mitochondria generate more than 90% of the energy your cells use. With age, mitochondrial efficiency declines: the organelles produce less ATP, generate more harmful reactive oxygen species, and lose their structural integrity. This creates a feedback loop — dysfunctional mitochondria trigger inflammatory signaling, which in turn further impairs mitochondrial function.

NAD+ is central to mitochondrial health through its role in activating SIRT1 and SIRT3 — mitochondrial deacetylases that support biogenesis (creation of new mitochondria) and quality control. A clinical trial published in Cell Reports Medicine in 2019 found that NR supplementation at 1,000 mg per day for 21 days increased NAD+ levels in skeletal muscle and upregulated the expression of mitochondrial function genes in older adults (Elhassan YS et al.). Exercise remains the most powerful non-pharmacological stimulus for mitochondrial biogenesis via PGC-1α activation.

Cells depend on a carefully regulated balance of protein synthesis, folding, and degradation — collectively called proteostasis. With age, the systems responsible for recognizing and clearing misfolded or damaged proteins — the proteasome and the unfolded protein response — become less effective. The result is an accumulation of toxic protein aggregates, a hallmark of neurodegenerative diseases including Alzheimer's and Parkinson's. Maintaining proteostasis requires adequate autophagy function, which in turn depends on the same foundational interventions: exercise, dietary optimization, and NAD+ sufficiency.