“Normal” only means “not sick.”
When a lab prints a reference range next to your result, it is not telling you what healthy looks like. It is telling you where most people already fall. A reference interval is built as a statistical band, usually the middle 95 percent of a sample population. By design, about 1 in 20 perfectly healthy people land outside it, and plenty of unwell people land inside. Clear it and you have learned one thing: you are not an outlier.
And that population is not a picture of health. It is largely sedentary, aging, and carrying the same slow problems as everyone else, so normal is anchored to how people typically are, not how a body performs at its best. Two people can both read within normal limits while one is quietly drifting toward disease and the other is genuinely thriving. The range was never built to tell them apart. It answers a single yes-or-no question, are you sick, and stops there.
1 in 20
Optimal asks a better question.
Optimal starts from a different place: where would your numbers sit if your body were working at its best? Those levels are not a matter of opinion. Across large bodies of research, the same ranges line up again and again with the lowest risk and the longest, healthiest lives, and they frequently sit well inside, or below, what a lab calls normal.
Blood pressure is the clearest example. For years a reading under 140 was treated as acceptable. The evidence has since moved. Two large randomized trials, ESPRIT in 2024 and BPROAD in 2025, found that driving systolic pressure below 120 prevented meaningfully more heart attacks, strokes, and deaths than the old under-140 target; in the diabetes trial alone, major cardiovascular events fell by about a fifth. In 2025 the American Heart Association and American College of Cardiology moved their goal to match, targeting below 130/80 and encouraging many people to reach below 120.
The same lower-and-earlier pattern holds elsewhere. For LDL cholesterol, the 2025 European cardiology and atherosclerosis guidelines push toward low targets reached sooner, because it is your cumulative lifetime exposure, not a single in-range reading, that drives heart disease. For blood sugar, risk begins climbing while you are still below the diabetes line, in the range a report would wave through. In each case, normal quietly tolerates a level the best evidence would not call good. Optimal is simply that higher standard, applied to every marker we grade.
It is also rare, and it is not improving. In one national analysis, only about 7 percent of U.S. adults had every major cardiometabolic marker at an optimal level at once. The most recent data point the same way: by 2021 to 2023, close to 2 in 5 adults met the criteria for metabolic syndrome, a cluster of the very markers we grade, and that share has been rising. Most people are told they are normal while sitting far from their best. That gap is the whole reason we exist.
7%
2 in 5
What your grade actually means.
We turn each of your numbers into a single letter, A+ through F, measured against that optimal standard rather than the normal range. An A means your result sits where the best evidence says it should for long-term health. It is not a gold star for being average.
A lower grade is not a diagnosis or a verdict. It is a target. A C is the clearest possible signal of where your single biggest opportunity is, the one change most likely to move your health. The point of a grade is that you can read it in a second, without a medical degree, and know exactly where you stand and where to aim.
What Biological Age really is.
Your body has an age that does not always match your birthday, and that is now well established science. Researchers have built a series of biological clocks that estimate how old you are functioning from the body's own signals. The early ones read DNA; the newest read the blood. In 2024, a clock built from a few hundred blood proteins, measured in tens of thousands of people, predicted death and the risk of eighteen major age-related diseases better than counting birthdays. Other recent work has shown that individual organs, the heart, the brain, the immune system, can age at different rates within the same person, and that a blood sample can reveal it.
18 diseases
Your Biological Age in Body By Numbers works in that spirit, though not with those exact research tools. We translate your everyday markers into one number that reflects how your body appears to be functioning, so a wall of separate results becomes something you can hold in your head and watch move. It is an estimate built for understanding and motivation, not a diagnosis and not a prediction of how long you personally will live. Treat it as a compass, not a crystal ball.
Grounded in evidence, kept current.
The optimal targets behind every grade are drawn from established, peer-reviewed research in longevity and cardiometabolic health, and they are reviewed by a licensed physician. As that science advances, and lately it is advancing fast, the standard advances with it.
Body By Numbers is a general wellness tool, not a medical diagnosis. Your grades and your Biological Age are built to help you understand your health and aim higher, not to diagnose, treat, or replace care from your doctor. Always discuss your results, and any changes to your health routine, with a qualified physician.
Further reading.
Some of the studies and guidelines that inform how we think about optimal health and biological age, leading with the most recent. They describe the broader science; they are not a validation of our specific thresholds or scores.
- 01
Only about 7% of U.S. adults have every major heart-and-metabolism marker at an optimal level at once.
O'Hearn M, Lauren BN, Wong JB, Kim DD, Mozaffarian D. Trends and Disparities in Cardiometabolic Health Among US Adults, 1999-2018. Journal of the American College of Cardiology. 2022;80(2):138-151.
View source - 02
In the most recent national data (2021 to 2023), about 2 in 5 U.S. adults (38.5%) met the criteria for metabolic syndrome, and the share has been rising.
Abohashem S, Hassan I, Wasfy JH, Taub PR. Trends and Prevalence of the Metabolic Syndrome Among US Adults. JAMA. 2026;335(3):274-277.
View source - 03
A lab's normal range is a statistical band from a reference population, built so about 1 in 20 healthy people fall outside it, so being in range is not the same as being optimal.
Timbrell NE. The Role and Limitations of the Reference Interval Within Clinical Chemistry and Its Reliability for Disease Detection. British Journal of Biomedical Science. 2024;81:12339.
View source - 04
In 2025, major U.S. guidelines set the blood-pressure treatment goal below 130/80 and encourage reaching below 120 for many people, lower than the older under-140 standard.
2025 AHA/ACC and multisociety Guideline for the Prevention, Detection, Evaluation and Management of High Blood Pressure in Adults. Hypertension. 2025. doi:10.1161/HYP.0000000000000249.
View source - 05
In more than 11,000 high-risk adults, aiming for systolic pressure below 120 rather than below 140 prevented more heart attacks, strokes, and deaths.
ESPRIT Collaborative Group. Lowering systolic blood pressure to less than 120 mm Hg versus less than 140 mm Hg in patients with high cardiovascular risk. The Lancet. 2024;404(10449):245-255.
View source - 06
In nearly 13,000 adults with type 2 diabetes, an intensive blood-pressure target below 120 cut major cardiovascular events by about a fifth.
Bi Y, Li M, Liu Y, et al. Intensive Blood-Pressure Control in Patients with Type 2 Diabetes (BPROAD). New England Journal of Medicine. 2025;392(12):1155-1167.
View source - 07
Updated 2025 European guidelines push LDL cholesterol to low targets reached earlier, because cumulative lifetime exposure, not a single in-range reading, drives heart-disease risk.
European Society of Cardiology and European Atherosclerosis Society. 2025 Focused Update of the 2019 ESC/EAS Guidelines for the management of dyslipidaemias. European Heart Journal. 2025;46(42):4359.
View source - 08
Across roughly 700,000 people, higher blood sugar tracked with higher risk of heart attack and stroke, even within the non-diabetic range.
The Emerging Risk Factors Collaboration. Diabetes mellitus, fasting blood glucose concentration, and risk of vascular disease: a collaborative meta-analysis of 102 prospective studies. The Lancet. 2010;375(9733):2215-2222.
View source - 09
Even before blood sugar reaches the diabetes threshold, prediabetes-range levels are linked to higher risk of cardiovascular disease and death.
Cai X, Zhang Y, Li M, et al. Association between prediabetes and risk of all cause mortality and cardiovascular disease: updated meta-analysis. BMJ. 2020;370:m2297.
View source - 10
A biological-age clock built from a few hundred blood proteins, in tens of thousands of people, predicted mortality and the risk of 18 major age-related diseases better than age alone.
Argentieri MA, et al. Proteomic aging clock predicts mortality and risk of common age-related diseases in diverse populations. Nature Medicine. 2024;30(9):2450-2460.
View source - 11
Individual organs can age at different rates within the same person, and a blood sample can reveal which ones are aging faster.
Oh HSH, Rutledge J, Nachun D, et al. Organ aging signatures in the plasma proteome track health and disease. Nature. 2023;624(7990):164-172.
View source - 12
A leading review lays out the twelve biological processes that drive aging, the framework scientists use to understand and measure how the body ages.
Lopez-Otin C, Blasco MA, Partridge L, Serrano M, Kroemer G. Hallmarks of aging: An expanding universe. Cell. 2023;186(2):243-278.
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