Vitals Age: what your watch can and cannot tell you

Plenty of people have no blood panel. Plenty of people have a watch. Vitals Age is Delta's answer to that gap: an adaptive-age proxy built from wearable signals, computed deterministically, wearing its uncertainty openly.

What goes in

Three signals, each with published mortality or health-outcome associations behind it:

• Resting heart rate. A 2010s meta-analysis in CMAJ pooled cohorts totalling over a million people and found higher resting HR associated with higher all-cause mortality, with the relationship strengthening above roughly 70–75 bpm.
• Heart-rate variability (HRV). Meta-analyses of prospective studies link lower HRV — specifically the low-frequency and total-power components — to elevated mortality and cardiovascular-event risk.
• Sleep duration. The association between sleep length and health outcomes is consistently U-shaped: both short and long sleep track with worse outcomes, with the commonly cited trough in the seven-to-eight-hour range.

Cardiorespiratory fitness, where a device estimates it, adds further signal — wearable-derived VO₂-max correlates strongly with survival in the published literature.

What comes out

One number, in years, wearing a band roughly twice as wide as the blood-grade Adaptive Age's. The width isn't a defect. A blood panel measures nine specific biomarkers with decades of validation behind them; a watch measures three loosely-related proxies filtered through an estimated algorithm. Pretending both deserve the same confidence would be the actual defect.

The per-signal dose-response curves are pinned to the published headline ratios at their stated anchor points; the curve shapes between anchors, and the de-overlap weighting, are documented approximations — flagged as such, swapped the moment a published composite spec exists.

Two hard rules

Vitals Age is a LEVEL, never a DYNAMICS signal. It is a slow-moving trailing estimate — a stand-in for the multi-year Adaptive-Age gap until you have bloodwork. Never does it feed the 48-hour-fast response curve. Wearable signals moving during a fast (HRV dipping, resting HR shifting) are interesting, but they are not this score's business, and the module has no fast-awareness at all.

It is never labelled "Adaptive Age". Adaptive Age is the blood-grade metric, validated against mortality in a large cohort. Vitals Age is a wellness-lane proxy. Same app, different lane, never confused — because a number that borrows credibility it didn't earn is worse than no number.

If you have both

Bloodwork and watch data sit side by side, clearly separated. The watch lane tells you something today, for free; the blood lane is the one that survives scrutiny. When you eventually scan a panel, nothing about the proxy contaminates the score — deterministic arithmetic keeps its inputs clean.