Part 4
Know Your Numbers
Picture a couple in their fifties who each spend $499 on a “biological age” test. His says 44. Hers says 61. He celebrates. She cries. Neither result changes a single thing their doctor would do. Meanwhile, neither of them has had a blood pressure reading in three years. Testing is powerful when it changes a decision. Otherwise it is an expensive mood.
Clinical scenes in this edition are explicitly labeled illustrations. They describe imagined situations used to explain medical decisions, not documented patients, diagnoses, conversations, or treatment outcomes. They should not be read as evidence that a particular intervention works. Personal recollections are recollections, not medical records.
Evidence grade (draft mapping). 13 questions; a question with mixed evidence counts under each grade.
- 43. What is “biological age”?It is an estimate of how worn your body is compared with the average person of your calendar age. It is a useful idea and, so far, an imprecise measurement.JClinical judgment / author synthesis
- 44. What is an epigenetic clock?A test that reads chemical tags on your DNA and uses them to estimate your biological age or your speed of aging.CObservational
- 45. Which clock is the best?For predicting who gets sick and who dies, GrimAge and DunedinPACE perform best in research. No clock is yet good enough to steer treatment for one individual.Grade pending
- 46. Should I buy one of these tests?Only if you understand it is a curiosity, not a diagnosis. It should never replace standard testing, and you should never pay for a treatment because of it.FNot demonstrated / insufficient
- 47. Which ordinary blood tests matter most?Start with tests that answer a clinical question. There is no universal longevity panel that every healthy adult needs yearly.GGuideline-based / consensus
- 48. What is VO2 max, and why does everyone say it predicts lifespan?VO2 max is the most oxygen your body can use during hard exercise. It is one of the strongest predictors of how long you will live.CObservational
- 49. What simple strength and balance tests can I do at home?Grip strength, standing up from a chair, walking speed, and balancing on one leg each predict health surprisingly well.CObservational
- 50. What is a DEXA scan, and is it worth it?A DEXA is a very low-radiation scan that measures bone density and, on many machines, muscle and fat. For bone it is essential. For body composition it is useful and optional.GGuideline-based / consensus
- 51. Should I get a full-body MRI?For most healthy people, no. It finds many things, and most of them are harmless, which starts a chain of worry, repeat scans, and sometimes biopsies.FNot demonstrated / insufficient
- 52. Should I wear a continuous glucose monitor if I do not have diabetes?As a two-to-four-week experiment, it can teach you something. As a permanent accessory for a healthy person, there is no evidence it improves health.BLimited or small human studies
- 53. Are sleep trackers and smart rings accurate?Good for total sleep time, resting heart rate, and trends. Poor at telling deep sleep from light sleep.Grade pending
- 54. How often should I repeat all this testing?Repeat testing when the result could change care. The interval depends on your risk, your previous result, and whether treatment has changed.GGuideline-based / consensus
- 55. What are the tests most doctors do not order that you wish they would?Lp(a) once in adulthood, and ApoB when it helps resolve risk, deserve wider discussion. A calcium score is useful when it could change a treatment decision.GGuideline-based / consensus