The scientific difference between getting older and actually ageing

You know someone who is 60 but seems 45. You know someone who is 38 but feels older than they should.

Most of us assume this is genetics, lifestyle, or luck. And partly it is. But there is now a more precise answer — one emerging from cellular biology, epigenetics, and longevity research — that reframes ageing not as an inevitability we submit to, but as a process that unfolds at different rates in different bodies.

The key distinction is between chronological age — the number on your passport — and biological age, which reflects how your cells, tissues, and organs are actually functioning.

They are not the same thing. And the gap between them may be one of the most meaningful health metrics we have.

The hallmarks of ageing

In 2013, a landmark paper published in Cell by Carlos López-Otín and colleagues formalised what researchers now call the "hallmarks of ageing" — nine cellular and molecular processes that, when they accumulate, drive the progression from biological youth to decline.

These hallmarks include:

• Genomic instability (accumulation of DNA damage)
• Epigenetic alterations (changes in how genes are expressed without altering the underlying DNA)
• Mitochondrial dysfunction
• Cellular senescence (cells that stop dividing but do not die, secreting inflammatory signals)
• Stem cell exhaustion
• Altered intercellular communication

What is striking about this framework is that it is not deterministic. These processes unfold at different rates depending on environment, nutrition, stress, sleep, and — crucially — the availability of certain cellular molecules. Including NAD+.

The epigenetic clock

One of the most significant developments in longevity science has been the development of epigenetic clocks — mathematical models that estimate biological age from patterns of DNA methylation (chemical modifications to DNA that regulate gene expression).

The most established of these, developed by Dr Steve Horvath at UCLA, can predict biological age from a blood or tissue sample with striking accuracy. And critically, it shows that biological age and chronological age diverge — sometimes substantially.

People who exercise regularly, eat well, manage stress, and maintain healthy metabolic markers tend to show lower biological ages. People under chronic stress, with poor sleep or significant inflammation, tend to show the reverse. This is not a metaphor. It is measurable biology.

Where NAD+ fits in

Several of the hallmarks of ageing are directly connected to NAD+ availability.

Mitochondrial dysfunction accelerates as NAD+ declines, because NAD+ is essential to the electron transport chain that powers mitochondrial ATP production. DNA repair slows because the enzyme PARP1, a key participant in repairing DNA strand breaks, consumes NAD+ in large quantities — when NAD+ is limited, PARP1 activity is constrained. And sirtuin-dependent gene regulation falters because sirtuins require NAD+ to function.

This is why NMN has attracted serious scientific attention not just as an energy supplement, but as a potential tool for what researchers call healthspan extension — not necessarily living longer, but functioning better for longer.

The difference that matters

The popular framing of longevity science — "anti-ageing," "turning back the clock" — creates unrealistic expectations and, in some cases, misleading product claims. At thecary, we are careful to avoid this language.

What the science actually supports is more nuanced and, in our view, more interesting: that the rate of biological ageing is not fixed, that cellular health is meaningfully influenced by how we nourish our cells, and that certain molecules — like NMN — appear to support the maintenance of cellular functions that decline with age.

Getting older is inevitable. The rate at which your cells age alongside you is, at least in part, something you can influence.

Frequently Asked Questions

Can I measure my biological age?

Yes. Epigenetic age testing is available commercially. Companies like Chronomics and TruMe (UK-based) offer DNA methylation analysis from saliva samples. It is an emerging rather than fully standardised field, but the science underpinning it is robust.

Do supplements alone reduce biological age?

No supplement should be positioned as a standalone solution. The evidence supports a systems-based approach: sleep, movement, nutrition, stress management, and targeted supplementation working together.

How does NMN relate to resveratrol?

Resveratrol is a polyphenol that activates sirtuins — but only when NAD+ is available. They are often discussed together in longevity research because they work synergistically: NMN provides the NAD+ substrate; resveratrol directs sirtuin activity.