A drop of blood can tell you what stage of life a person is at. Scientists took 54 blood markers from 11,124 people aged 12 to 80 and plotted each test as a point on a map. The points didn't scatter randomly: they lined up along two lines. The first line separates men from women. In the teenage years they diverge, in adulthood the gap is widest, and by old age they converge again. The second line counts out age, and along it you can see how blood changes over the years.
With this map, you can measure how fast a person moves along life's path. It turned out that in women the pace rises sharply between 40 and 60, when menopause sets in. After 75, everyone speeds up. But the most important finding: in people without chronic diseases, the trajectory is shifted toward youth. By age 79, their body looks as if they were 63, that is, 16 years younger than the average person of the same age. Obesity, smoking and depression also push a person forward along the map, but each factor kicks in at its own age.
Earlier, scientists tried to reduce the body's age to a single number, but now it's clear that you need at least two coordinates: sex and age. This map helps us understand that aging is not a smooth fading but a road with varied stretches, faster in some places, slower in others. And it lets us compare the health of different groups of people to understand how diseases and lifestyle speed up our journey.
By age 79, healthy people lag behind the general population along the physiological trajectory by 16 years, meaning their body looks as if they were 63.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.