Sirtuins

Sirtuins are a family of seven human enzymes, SIRT1 through SIRT7, that remove acetyl and related chemical tags from other proteins and can only do so by consuming NAD+, a coenzyme central to cell metabolism. Because NAD+ is their fuel, sirtuins are most active when a cell reads as energy-poor and quieter when it is well fed. Several of their targets are the histone proteins that DNA is wound around, so a sirtuin can change which genes are readable without changing the DNA sequence itself. They are named after Sir2, the yeast gene where the family was first described.

What it measures

Sirtuins are proteins, not a test result. The seven human members sit in different parts of the cell: SIRT1, SIRT6 and SIRT7 work mainly in the nucleus, SIRT2 mainly in the cytoplasm, and SIRT3, SIRT4 and SIRT5 inside mitochondria. Each acts on its own set of target proteins, and each reaction splits a molecule of NAD+. That coupling is the interesting part, because it ties the activity of these enzymes to how much spare NAD+ the cell has.

There is no routine clinical test for sirtuin activity. Research labs infer it indirectly, from how heavily known target proteins are acetylated in a tissue sample, from gene expression, or from NAD+ concentrations measured in blood or tissue. No consumer lab panel can report “your sirtuin level”, and any product that claims to measure one should be treated with suspicion.

Why it matters for longevity

Much of the popular interest in Sirtuins traces back to yeast, where extra copies of Sir2 extended replicative lifespan, with similar early reports in worms and flies. Those findings were influential and also contested: later work under more tightly controlled genetic conditions found much smaller effects, or none, and the field moved on to narrower claims. In mice, extra SIRT6 has been reported to extend lifespan and extra SIRT1 to improve metabolic health, with results that differ by strain, sex and diet.

In humans the evidence is thinner and almost entirely observational or mechanistic. NAD+ levels fall in many tissues with age, which would limit how much work sirtuins can do, and sirtuin-dependent pathways overlap with DNA repair, mitochondrial quality control and inflammation — all processes that track with aging. But no human trial has shown that raising sirtuin activity extends life or slows a biological-age measure. It is more accurate to treat sirtuins as one node in the nutrient- and energy-sensing network that also contains AMPK, the sensor that switches on when cellular energy runs low. The growth-promoting arm of the same network, mTOR, pulls in the opposite direction.

What changes it

You cannot dose a sirtuin directly, so every lever is indirect.

  • Energy status. Fasting, exercise and sustained calorie restriction raise NAD+ availability and sirtuin signaling in animal models. In people the same behaviors clearly improve metabolic markers; whether that runs through sirtuins is inferred, not demonstrated.
  • NAD+ precursors. Nicotinamide riboside and NMN reliably raise blood NAD+ in human trials. Raising the substrate is not the same as proving a benefit, and trials so far have not shown slowed aging.
  • Resveratrol. It was first described as a direct SIRT1 activator, but that activation depended heavily on the fluorescent tag used in the original assay, and it largely disappeared with natural substrates. Human bioavailability is poor and no longevity benefit is established.
  • Sleep and circadian rhythm. NAD+ production oscillates across the day, so chronically disrupted sleep plausibly blunts sirtuin signaling — a mechanistic argument, not a proven one.
  • Age and genetics. The age-related decline in NAD+ and your inherited sirtuin variants are not things you control.

Related reading

Disclaimer. This article is for information only and does not replace medical advice. Talk to a qualified clinician before changing anything about your health.