Blood Age explained: how 18 blood markers are turned into a biological age

What is Blood Age?

Blood Age answers one question about your blood test: does it look like the blood of someone your age?

It combines 18 routine markers from a single draw into a figure in years. If you are 45 and it comes back 49, your markers resemble those of someone four years older, by our model.

Test again in six months and you can get a different figure, because the markers themselves move.

How Blood Age is estimated

Everything comes from one blood draw. The markers fall into seven groups, by what they measure.

• Blood sugar: HbA1c, which reflects your average blood sugar across the previous two to three months

• Inflammation and immune cells: C-reactive protein, made by the liver in response to inflammation, plus white blood cell count and lymphocyte percentage, the share of white cells that are lymphocytes

• Red blood cells: hemoglobin, the protein that carries oxygen, plus mean corpuscular volume (the cells' average size) and red cell distribution width (how much their size varies)

• Kidneys: creatinine, a waste product that builds up in the blood when the kidneys aren't working well, and estimated glomerular filtration rate (eGFR), a calculation used to estimate how well your kidneys filter

• Liver: albumin (a protein the liver makes), plus alkaline phosphatase, ALT and AST (enzymes found in the liver)

• Blood fats: total cholesterol, LDL cholesterol, HDL cholesterol and triglycerides

• Thyroid: TSH, or thyroid-stimulating hormone

We built Blood Age on published research. Your Ring plays no part in it, and every new blood panel can give you a new figure.

Why these 18 markers

All of them are routine lab tests, so a standard panel usually covers them.

We chose them to span the body's main systems, because the body does not age evenly. Among UK adults in one study, different organ systems aged at different paces, and people with a disease in one organ often had older biological ages in several others.

How to read your Blood Age

Start with the difference between your Blood Age and your actual age. Then open the results underneath it and read them one by one, as the app lists them. If one sits outside its reference range, that stands on its own, whatever your Blood Age is.

Illness moves it. An infection can push up your C-reactive protein and your white cell count for a week or two. So get tested when you are well, and prepare the same way every time, including any fasting your test asks for.

Compare yourself with yourself. Different methods of estimating biological age often disagree, so your own previous Blood Age is a better comparison than a biological age from a different kind of test. You learn more from two or more tests than from one, though illness and laboratory variation can move the figure too.

What the research says

People with more diseases tend to have an older biological age, judged from routine lab results. That comes from a study of more than 11,000 US adults.

Among more than 400,000 UK adults, the more unhealthy habits someone had, the further their blood-based estimate ran ahead of their actual age. The study counted smoking, alcohol-related habits and too little exercise.

Sleep showed up too, but faintly. About 364,000 UK adults with healthier sleep habits had younger-looking estimates, by roughly five to six weeks of biological age for each point on a sleep scale scored from 0 to 6. That is under a year across the whole scale.

Cutting calories slowed two of these measures in a two-year trial of 220 adults without obesity. People randomly assigned to eat less aged more slowly, according to both biological-age measures, than people who carried on as usual, and the difference remained after accounting for weight loss. It does not follow that slowing these measures extends life.

The methods also disagree with each other. Among 964 middle-aged adults in New Zealand, estimates of biological age built in different ways matched one another poorly.

None of these studies tested Blood Age itself. Each used a different estimate of biological age.

What Ultrahuman's data shows

We looked at 20,858 members. Those whose Blood Age sat further above their actual age tended to have a higher resting heart rate at night, and to sleep less. That is reported in a preprint, shared before peer review.

Of five Ring measures, night-time resting heart rate came closest to the Blood Age difference, and even that was a loose connection once we accounted for age and sex, a correlation of 0.22.

These are associations in observational data. Sleeping more or lowering your heart rate would not necessarily change your Blood Age, and the members we studied may not look like the wider population.