Hemoglobin is the iron-containing protein inside red blood cells that binds oxygen in the lungs and releases it to the tissues. Each molecule is built from four globin chains, each folded around a heme group holding one iron atom, so a single molecule carries up to four oxygen molecules. It also helps carry carbon dioxide back to the lungs. On a lab report it is the number that decides whether you are anemic. It is not glycated hemoglobin (HbA1c), which is only the fraction of your hemoglobin that blood sugar has stuck to, read as a glucose marker.
What it measures
Hemoglobin comes off a complete blood count taken from an ordinary venous draw, reported in g/dL in the US and in g/L in most other countries. The value is a concentration, so anything that shifts plasma volume moves it without changing how much hemoglobin you own: dehydration pushes it up, pregnancy and heavy endurance training push it down by dilution. Hematocrit and red blood cell count describe the same cells from other angles, while mean corpuscular volume and mean corpuscular hemoglobin – cell size, and hemoglobin per cell – point toward the cause when the value is low. For a deeper reference, see the Hemoglobin entry at Smart Longevity.
Typical values
| Reading | What it generally means |
|---|---|
| Roughly 13.5-17.5 g/dL (135-175 g/L) in men | A common adult reference interval, though each laboratory sets its own limits |
| Roughly 12.0-15.5 g/dL (120-155 g/L) in women | Same caveat; from puberty onward women run lower than men |
| Under 13 g/dL in men, under 12 g/dL in non-pregnant women, under 11 g/dL in pregnancy | Anemia, by the long-standing WHO definition |
| Above your laboratory’s upper limit | Wants an explanation: dehydration, smoking, altitude, lung disease, sleep apnea, testosterone therapy, a marrow disorder |
These intervals are not universal. They shift with sex, age, pregnancy and the altitude you live at – people living high above sea level carry more hemoglobin – and children have ranges of their own. Read your result against the interval printed on your own report and against your earlier results: a fall of a couple of g/dL inside the normal band can matter more than one value sitting just under it.
Why it matters for longevity
Anemia grows more common with each decade of adult life, and in older adults it is associated in observational cohorts with higher all-cause mortality, more frailty and falls, and faster cognitive decline – mild anemia included. The relationship looks U-shaped: values above the reference range carry higher risk too, partly through thicker, more clot-prone blood. Most of that risk is probably not caused by the number itself. A low hemoglobin is usually the visible end of something else – slow gastrointestinal bleeding, heavy periods, iron or B12 deficiency, chronic kidney disease, the anemia of chronic inflammation – which is why a falling hemoglobin in an older adult is a reason to hunt for a cause, not a normal feature of aging.
What changes it
Iron is the usual lever. Ferritin, which reflects stored iron, falls before hemoglobin does, so a normal hemoglobin next to a low ferritin is still iron deficiency and can still cause symptoms. Heme iron from meat and fish absorbs best; vitamin C improves absorption of plant iron, while tea and coffee reduce it. Vitamin B12 and folate are needed to build red cells at all. The bigger levers are usually stopping a leak or treating a disease: heavy menstrual bleeding, gastrointestinal blood loss, frequent donation, kidney disease that blunts erythropoietin. Weeks at altitude raise hemoglobin, and so does smoking, because carbon monoxide crowds oxygen off the molecule. Some of it is not yours to move: your sex, and inherited traits such as thalassemia trait, which keeps hemoglobin low for life. Do not start iron on a hunch: it does nothing for anemia that is not iron-related, and iron overload does real harm.
Related reading
- Which Blood Tests Reflect Aging and How to Read Them
- VO2 Max: Why Aerobic Fitness Predicts Longevity
- How to Build a Longevity Supplement Plan
Disclaimer. This article is for information only and does not replace medical advice. Talk to a qualified clinician before changing anything about your health.