This glossary defines the biomarkers, aging clocks and physiological concepts that come up across Longevity Lab. Each entry explains what the term is, what a value actually measures, what the evidence links it to, and what moves it. They are written to be read in thirty seconds and skimmed for the number you came for.
If you arrived from an article, the term you clicked is below. If you are starting here, the entries on biological age, healthspan and VO2max are the ones the rest of the site leans on most.
Where a term has a calculator or a reference table behind it, we point to one. Our companion site keeps a longer Medical glossary covering several hundred laboratory and clinical terms, and its entries on Biological age and Healthspan (healthy life expectancy) go deeper into the measurement side than we do here.
A
- AlbuminAlbumin is the most abundant protein in blood plasma, made by the liver. What the test measures, usual adult r…
- Alkaline phosphatase (ALP)Alkaline phosphatase (ALP) is an enzyme from the bile ducts and bone. What the blood test measures, the typica…
- Allostatic loadAllostatic load is the cumulative wear on the body from long-term stress, scored from cortisol, inflammation,…
- Alzheimer’s diseaseAlzheimer’s disease is the most common cause of dementia: beta-amyloid plaques, tau tangles and dying neurons.…
- Amino acidsAmino acids are the building blocks of every protein in the body: what the 20 standard and 9 essential ones do…
- AMPKAMPK is the enzyme that senses low cellular energy and switches cells from building to burning. What it does,…
- AmyloidAmyloid is a misfolded protein that clumps into insoluble deposits; in the brain, beta-amyloid plaques. How am…
- AnemiaAnemia is a shortage of hemoglobin or red blood cells, so blood carries less oxygen. What the blood count show…
- AnxietyAnxiety is anticipatory fear about a threat that has not arrived: how normal anxiety differs from an anxiety d…
- ApoptosisApoptosis is programmed cell death: what it is, how it differs from necrosis, why the body needs it, and how i…
- ASCVDASCVD 10-year risk is the estimated chance of a first heart attack or stroke within ten years: what goes into…
- AtherosclerosisAtherosclerosis is the slow buildup of cholesterol-rich plaque in artery walls. What it is, how it is measured…
- Atrial fibrillationAtrial fibrillation is a fast, disorganized heart rhythm: how it is found on an ECG, why it raises stroke and…
- AutophagyAutophagy is how a cell breaks down and recycles its own damaged parts. What it is, how fasting, exercise and…
B
- Biological ageBiological age is an estimate of your body's condition from biomarkers, not your birth date: what it measures,…
- Biomarker of agingA biomarker of aging is a measurable indicator of how fast your body is aging: what qualifies as one, which te…
- Blood glucoseBlood glucose is the amount of sugar circulating in your blood. What a fasting test measures, the normal, pred…
- Blood pressure (BP)Blood pressure (BP) is the force of blood against artery walls, given as systolic over diastolic in mmHg. What…
- Blue zonesBlue zones are regions where an unusual share of people reach 90 or 100: which five they are, the habits resid…
- BMIBMI (body mass index) is body weight in kilograms divided by height in meters squared: the WHO categories, wha…
- Body compositionBody composition is the split of your body weight into fat mass and lean mass. What it measures, how it is ass…
- Bone densitometryBone densitometry is a low-dose X-ray scan of bone mineral density. What it measures, what a T-score means, an…
C
- C-reactive protein (CRP)C-reactive protein (CRP) is a liver-made marker of inflammation. What the blood test measures, how the hs-CRP…
- CalciumCalcium is the mineral stored in bone and used in trace amounts by nerves and muscle. What a blood calcium tes…
- Cardiorespiratory fitnessCardiorespiratory fitness is the body's ability to deliver and use oxygen during exercise. What VO2 max measur…
- Cardiovascular disease (CVD)Cardiovascular disease (CVD) is the umbrella term for heart and blood vessel disorders: what it covers, how ri…
- Celiac diseaseCeliac disease is an autoimmune reaction to gluten that damages the small intestine. What the antibody tests s…
- Cellular senescenceCellular senescence is when a damaged cell stops dividing for good but stays alive and inflames the tissue aro…
- Cholesterol (total)Total cholesterol is the sum of the cholesterol in all your blood lipoproteins. What the lipid panel reads, th…
- Chronic stressChronic stress is a stress response that never switches off: sustained HPA-axis and cortisol activation, how i…
- Chronological ageChronological age is the time since your birth, in years. What it measures, why it predicts risk, how it diffe…
- Circadian rhythmCircadian rhythm is the body's internal 24-hour clock, set by light and run from the hypothalamus. What it tim…
- Cognitive ageCognitive age is an estimate, in years, of how old your memory, attention and speed perform against age norms.…
- Cognitive agingCognitive aging is the normal, gradual slowing of thinking and recall with age: what is typical, how it differ…
- Cognitive reserveCognitive reserve is the brain's ability to keep working despite damage: what it means, how researchers measur…
- CortisolCortisol is the adrenal stress hormone that follows a daily rhythm. How it is measured, what a flat curve mean…
- CreatinineCreatinine is a muscle waste product the kidneys filter out of the blood, and its level is used to estimate GF…
D
- DementiaDementia is a lasting decline in memory, thinking and judgment that disrupts daily life. What causes it, how i…
- DEXADEXA is a low-dose X-ray scan that measures bone mineral density and body composition. What it measures, T-sco…
- Diastolic pressureDiastolic pressure is the lower blood pressure number: the pressure held in your arteries between heartbeats.…
- DNA methylationDNA methylation is a chemical tag on DNA that switches genes on or off. What it measures, how epigenetic clock…
- DNAm ageDNAm age is a biological age estimate read from DNA methylation patterns. What it measures, how to read the nu…
- DunedinPACEDunedinPACE is an epigenetic clock that measures the pace of aging as a ratio of biological years per calendar…
E
- EndotheliumThe endothelium is the single-cell lining of every blood vessel. What it does, how endothelial function is tes…
- Epigenetic clockAn epigenetic clock estimates biological age from DNA methylation patterns. What it measures, how the numbers…
- EpigeneticsEpigenetics is how chemical marks switch genes on and off without changing the DNA itself. What it covers, how…
- Estimated biological ageEstimated biological age is the age a model assigns your body from blood tests and blood pressure: what it mea…
F
- Fat-free mass (FFM)Fat-free mass (FFM) is all the body weight that is not fat: muscle, bone, organs and water. What it measures,…
- FerritinFerritin is the protein that stores iron in your cells; the blood test estimates your iron reserves. What it m…
- Fitness ageFitness age is your cardiorespiratory fitness expressed in years: what it measures, how calculators estimate i…
- FolateFolate is vitamin B9, used to build DNA and carry methyl groups. What serum and red cell folate tests show, th…
G
- Genetic ageGenetic age is the share of your aging and lifespan set by inherited DNA. What it covers, how it differs from…
- Gestational diabetesGestational diabetes is high blood glucose first detected in pregnancy. The glucose tolerance test cut-offs, w…
- Glycated hemoglobin (HbA1c)HbA1c (glycated hemoglobin) is the share of hemoglobin with glucose attached: a running average of blood sugar…
- GrimAgeGrimAge is a second-generation epigenetic clock that estimates mortality risk from DNA methylation in blood: w…
- Gut microbiomeThe gut microbiome is the community of microbes living in your digestive tract, mostly the colon. What it does…
H
- HDLHDL is high-density lipoprotein, the particle that carries cholesterol back to the liver. What HDL cholesterol…
- HealthspanHealthspan is the part of life lived in good health, free of chronic disease and disability. How healthspan di…
- Heart rate zonesHeart rate zones are pulse ranges used to dose exercise intensity. What the five zones train, how they are cal…
- HemoglobinHemoglobin is the iron-rich protein in red blood cells that carries oxygen. What the blood test measures, usua…
- HomocysteineHomocysteine is an amino acid made when the body processes methionine. What a raised homocysteine level means,…
- HormesisHormesis is the pattern where a small dose of stress - exercise, heat, cold, fasting - strengthens the body wh…
- hs-CRPhs-CRP is a high-sensitivity blood test for C-reactive protein, a marker of low-grade inflammation used in car…
- HyperparathyroidismHyperparathyroidism is the overproduction of parathyroid hormone by the parathyroid glands. What primary, seco…
- HypothyroidismHypothyroidism is an underactive thyroid gland making too little hormone. What the TSH and free T4 pattern sho…
I
- IGF-1IGF-1 (insulin-like growth factor 1) is the hormone that does growth hormone's work. What the blood test shows…
- Inflammatory markersInflammatory markers are blood tests — CRP, hs-CRP, ESR, fibrinogen, ferritin, IL-6 — showing how much inflamm…
- InsulinInsulin is the pancreatic hormone that moves glucose from blood into cells. What a fasting insulin test shows,…
- Insulin resistanceInsulin resistance is when muscle, fat and liver cells respond poorly to insulin, so the pancreas makes more.…
- Intermittent fastingIntermittent fasting is an eating pattern that alternates set eating windows with periods of no calories. What…
- Iron deficiencyIron deficiency is a shortage of usable iron that empties your stores long before hemoglobin falls. What ferri…
L
- Laboratory testsLaboratory tests are analyses of blood, urine and other samples that measure a specific substance. What refere…
- Lean muscle massLean muscle mass is the weight of your skeletal muscle, counted apart from fat and bone. What it measures, typ…
- LongevityLongevity is how long a person or population actually lives, and the science of extending it. How it differs f…
M
- MACEMACE, or major adverse cardiovascular events, is the composite trial endpoint counting cardiovascular death, h…
- MagnesiumMagnesium is an essential mineral and cofactor in over 300 enzyme reactions. What the blood test shows, normal…
- MCVMCV (mean corpuscular volume) is the average size of your red blood cells. What the blood count measures, usua…
- Mediterranean dietThe Mediterranean diet is an eating pattern built on vegetables, legumes, whole grains, olive oil and fish. Wh…
- Metabolic syndromeMetabolic syndrome is a cluster of five risk factors - waist, triglycerides, HDL, blood pressure, glucose - di…
- MetabolismMetabolism is the full set of chemical reactions that turn food into energy and body tissue: what it measures,…
- MethionineMethionine is an essential sulfur amino acid that begins every protein and supplies SAM for methylation. What…
- METS-IRMETS-IR is an insulin resistance score calculated from fasting glucose, triglycerides, HDL and BMI, with no in…
- Mild cognitive impairment (MCI)Mild cognitive impairment (MCI) is measurable decline in memory or thinking that does not yet cost independenc…
- MitochondriaMitochondria are the organelles that turn food and oxygen into ATP, the cell's energy. What they do, why they…
- MTHFRMTHFR is the gene for the enzyme that activates folate. What the C677T variant does, how it affects homocystei…
- mTORmTOR is the cell's nutrient sensor that decides between growth and repair. What it does, how food, exercise an…
N
- NeurodegenerationNeurodegeneration is the progressive loss and death of neurons. What it is, how it is measured, why it drives…
- NeuroinflammationNeuroinflammation is the immune response of brain tissue, run by microglia. How it is measured, why chronic ac…
- Neuromotor functionNeuromotor function is how the nervous system controls movement: balance, coordination and motor units. How it…
- NeuronsNeurons are the cells that carry and process signals in the brain and nerves. What they are, how they change w…
O
- OsteopeniaOsteopenia is moderately low bone density, a T-score between -1.0 and -2.5 on a DXA scan. What the number mean…
- OsteoporosisOsteoporosis is a bone disease in which low density and damaged structure make fractures likely. What a T-scor…
- Oxidative stressOxidative stress is an imbalance between reactive oxygen species and the body's antioxidant defenses. What it…
P
- Parathyroid hormone (PTH)Parathyroid hormone (PTH) is the hormone that keeps blood calcium steady. What the test measures, how it is re…
- Perceived stressPerceived stress is how far you judge life to be unpredictable and beyond your control. What the Perceived Str…
- PhenoAgePhenoAge is a biological age in years, calculated from nine routine blood markers plus chronological age and f…
- PrediabetesPrediabetes is blood sugar above normal but below the diabetes threshold. The fasting glucose, OGTT and HbA1c…
- Processing speedProcessing speed is how fast the brain takes in information and responds. What tests measure it, why it declin…
R
- RDWRDW (red cell distribution width) shows how much your red blood cells vary in size. What the test measures, us…
- Red blood cells (RBC)Red blood cells (RBC) are the oxygen-carrying cells of the blood. What the RBC count on a blood test measures,…
- Resting heart rateResting heart rate is how many beats per minute your heart makes at rest. What counts as normal, why a lower p…
S
- SarcopeniaSarcopenia is the age-related loss of skeletal muscle mass and strength. What it measures, the cut-offs clinic…
- SirtuinsSirtuins are seven NAD+-dependent enzymes, SIRT1 to SIRT7, that link a cell's energy state to gene activity. W…
- Skeletal muscle mass (SMM)Skeletal muscle mass (SMM) is the total weight of the muscle on your skeleton. What it measures, how DXA and b…
- StatinsStatins are drugs that lower LDL cholesterol by blocking HMG-CoA reductase. What they do, how dose intensity w…
- SteatohepatosisSteatohepatosis, or fatty liver, is fat stored inside liver cells. What it measures, how it is graded, why it…
- Stem cellsStem cells are unspecialized cells that renew themselves and rebuild tissue. What they are, why the reserve sh…
- StrokeStroke is sudden brain damage from a blocked or bleeding artery: the ischemic and hemorrhagic types, the FAST…
- Subcutaneous fatSubcutaneous fat is the fat layer stored just under the skin. What it is, how calipers and DEXA measure it, ho…
- Systolic pressureSystolic pressure is the top blood pressure number, the peak force in your arteries as the heart contracts. Wh…
T
- TelomeraseTelomerase is the enzyme that rebuilds the telomere caps on chromosomes. Where it is active, why adult cells s…
- TelomeresTelomeres are the repeating DNA caps at the ends of your chromosomes that shorten as cells divide. How they ar…
- The Hayflick limitThe Hayflick limit is the maximum number of times a normal human cell can divide before it stops for good. Wha…
- Total proteinTotal protein is the combined amount of albumin and globulins in blood serum. What the test measures, its usua…
- TriglyceridesTriglycerides are the main storage fat in the blood, read from a lipid panel. What the number measures, the us…
- Type 2 diabetesType 2 diabetes is a chronic condition where cells resist insulin and blood glucose stays high. How it is diag…
V
- Vascular ageVascular age is the age at which the average person's arteries match yours. How it is measured, what the numbe…
- Visceral fatVisceral fat is the deep abdominal fat stored around the liver, pancreas and intestines. What it is, how it is…
- Vitamin B12Vitamin B12 (cobalamin) is the vitamin behind red blood cells and nerve myelin. What the blood test shows, who…
- Vitamin CVitamin C (ascorbic acid) is an essential vitamin needed for collagen, iron absorption and antioxidant defense…
- Vitamin DVitamin D is a hormone-like nutrient measured in blood as 25-OH D: what the test shows, the ranges labs use, w…
- VO2maxVO2max is the maximum amount of oxygen your body can use per minute during all-out exercise. What it measures,…
W
Z
Disclaimer. These definitions are for information only and do not replace medical advice. Reference ranges vary by laboratory, assay, age and sex — always read your own results with a qualified clinician.