News · Longevity & Aging
Biological aging clocks diverged between women and men across 15 organ systems
Most biological age tests were trained on men and women together. Building 38 separate clocks shows organs age on different schedules by sex, with different genes and proteins behind them.
- Researchers built 38 sex-specific biological aging clocks covering 15 organ systems.
- Clocks estimate biological age from scans and blood measures, then subtract a person's actual age.
- Female and male clocks diverged markedly, and pooled models blur that difference.
- Genetic analyses and protein networks behind organ aging also differed by sex.
- The clocks predicted disease and death in sex- and organ-dependent ways, but remain research tools.
Two people born on the same day can have very different bodies at 60. That observation gave rise to biological age: models that guess your age from scans or blood, with the gap between guess and birthday treated as a measure of wear. Almost all of them were built from women and men pooled together.
A study in Nature Medicine took that assumption apart. Building separate clocks for each sex across 15 organ systems produced results that diverged, in the genes involved, the proteins behind them and what the clocks predicted.
What biological aging clocks are
MedlinePlus frames healthy aging around what people can influence: eating well, staying active, getting enough sleep and keeping up with checkups all help you stay healthy as you age. Chronological age tells a doctor how many years have passed, not how the body has fared.
That is the gap biological clocks try to fill. As the authors define them, they are artificial intelligence-predicted age minus chronological age, and most were trained on sex-pooled samples and implicitly assume sex invariance: that the aging process looks the same in women and men.
How the sex-specific clocks were built
The team developed 38 sex-specific biological aging clocks across 15 organ systems, training models separately in women and in men rather than together. That allows each person to be compared with a normal built from their own sex.
They then went beyond the scores. Genetic analyses, including Mendelian randomization, which uses inherited variants to probe cause and effect, tested how organ aging relates to other traits. Protein measurements mapped the biological networks involved, and survival analyses followed who developed disease or died.
What differed between women and men
The clocks did not agree with each other. The researchers reveal marked divergence between female and male clocks, meaning a pooled model would smooth over real differences in how organ systems age.
The differences ran deeper than the scores. Genetic results indicated that organ-specific aging liability and its relationships to cardiometabolic, endocrine and mental traits are configured differently in females and males, and proteomic analyses identified distinct, organ-resolved synaptic, immune, vascular and metabolic networks. In survival analyses the clocks predicted systemic disease and death in a sex- and organ-dependent way, and brain aging tracked with cognitive decline differently by sex within a preclinical Alzheimer’s trial.
Why sex-specific aging measures matter
Medicine has a long record of treating male bodies as the default and folding women in afterwards. Aging research inherited that habit, and this study is a concrete demonstration of what it costs: signals that appear in one sex can be diluted when both are modeled together.
It also matters for interpretation. If a clock says a woman’s heart is aging quickly, that claim only means something against a reference of other women’s hearts. The authors argue that sex-stratified clocks define biological age against sex-appropriate normative references and reveal signatures that pooled models may obscure.
What aging clock research cannot tell you
These are models, not measurements of a biological process. A clock that predicts age well may still be picking up illness, medication or lifestyle rather than aging itself, and a fast clock is not a diagnosis.
The analyses rest on large research cohorts, which skew healthier, better off and less diverse than the general population, and the genetic work carries the usual caveats about ancestry. Mendelian randomization strengthens causal inference but does not establish it. And nothing here validates any commercial biological age test.
What this changes about biological age tests
For anyone tempted by a direct-to-consumer aging score, the message is to wait. The field is still working out how to define normal, and this study shows that even the reference point depends on sex.
The levers that make a difference to how people age are unchanged and unglamorous: blood pressure, activity, sleep, smoking, alcohol, diet and keeping up with screening. Those are measurable today, and they have outcome data behind them.
People also ask
What did the study find?
Sex-stratified training produced marked divergence between female and male clocks. Genetic parameters and Mendelian randomization, meaning the use of inherited gene variants to probe cause and effect, indicated that organ-specific aging liability, and its links to heart, hormone and mental health traits, is configured differently in females and males. Proteomic analyses, meaning large-scale measurement of blood proteins, identified distinct organ-resolved networks, and the clocks predicted systemic disease and all-cause mortality in a sex- and organ-dependent manner.
What is a biological aging clock?
A model that predicts a person's age from biological data such as brain scans, blood proteins or metabolites. The gap between predicted and actual age is used as a measure of how fast someone appears to be aging.
Why does training separately by sex matter?
If a clock is trained on men and women together, its idea of normal is an average of both. Measuring an individual against a reference built from their own sex gives a more meaningful gap.
Which organs were covered?
Fifteen organ systems, including the brain, heart, liver, kidneys, lungs, immune and metabolic systems, each with its own clock.
Can I get my organ ages measured?
Commercial biological age tests exist, but they are not validated for clinical decisions, and this study's clocks are research models. A standard check of blood pressure, cholesterol, blood sugar and weight tells a doctor more.
What is the practical use?
For now, research: identifying who is aging faster in which system, and why that differs between women and men. Anything sold as an organ age score today should be treated with caution. This is general information rather than medical advice.