A hemoglobin level below 13.2 g/dL in men or below 11.6 g/dL in women is considered low. How far below that range you fall determines whether your situation is mild, moderate, or something that needs prompt attention. The good news: most cases of low hemoglobin stem from fixable causes, especially iron deficiency.
What Counts as Low
Hemoglobin is the protein inside red blood cells that carries oxygen from your lungs to every tissue in your body. It’s measured in grams per deciliter (g/dL) on a standard blood test, often part of a complete blood count (CBC). The healthy range is 13.2 to 16.6 g/dL for men and 11.6 to 15.0 g/dL for women.
If you’re pregnant, the thresholds shift. The World Health Organization defines anemia during pregnancy as hemoglobin below 11.0 g/dL in the first and third trimesters, and below 10.5 g/dL in the second trimester. Your blood volume increases significantly during pregnancy, which naturally dilutes hemoglobin concentration, so a slightly lower number is expected.
The WHO also grades severity, which helps you understand where you stand:
- Mild anemia: 11.0 to 12.9 g/dL in men, 11.0 to 11.9 g/dL in non-pregnant women, 10.0 to 10.9 g/dL in pregnant women
- Moderate anemia: 8.0 to 10.9 g/dL in men and non-pregnant women, 7.0 to 9.9 g/dL in pregnant women
- Severe anemia: below 8.0 g/dL in men and non-pregnant women, below 7.0 g/dL in pregnant women
One thing worth knowing: if you live at high altitude, your body produces more hemoglobin to compensate for thinner air. People living at 3,500 to 4,000 meters in Bolivia, for example, average about 17.9 g/dL for men and 16.8 g/dL for women, compared to 15.3 and 13.4 at sea level. So a “normal” reading at sea level could actually represent low hemoglobin for someone living in the mountains.
Why Low Hemoglobin Makes You Feel Awful
Hemoglobin is your oxygen delivery system. When levels drop, your tissues don’t get enough oxygen, and your body starts compensating in ways you can feel. Your heart beats faster to push more blood through. You breathe more quickly. Despite these efforts, you still can’t deliver oxygen as efficiently as normal, which is why the hallmark symptoms are fatigue, weakness, and shortness of breath, especially during physical activity.
Cold hands and feet happen because your body prioritizes oxygen delivery to vital organs, pulling blood flow away from your extremities. You might also notice dizziness when standing up, restless legs, pale skin, or a general sense of lethargy that sleep doesn’t fix. With more severe anemia, chest pain and a dramatic drop in exercise tolerance can develop. In extreme cases, the heart works so hard to compensate that it can lead to heart failure.
Many people with mild anemia don’t notice symptoms at all, or they attribute the tiredness to stress, poor sleep, or aging. This is why low hemoglobin often shows up as an incidental finding on routine bloodwork.
The Most Common Causes
Iron deficiency is by far the leading cause worldwide. Your body needs iron to build hemoglobin, and you can become deficient through three main pathways: not eating enough iron-rich foods, losing blood (heavy menstrual periods are a very common culprit), or not absorbing iron properly from your gut. Conditions like celiac disease or inflammatory bowel disease can interfere with absorption even if your diet is adequate.
Deficiencies in vitamin B12 and folate also cause low hemoglobin, though less frequently than iron. These vitamins are essential for producing healthy red blood cells, and without them, your body makes fewer cells or cells that are abnormally large and inefficient.
Chronic diseases are another major category. Long-term inflammation from conditions like rheumatoid arthritis, infections, cancer, or liver disease can suppress red blood cell production. Chronic kidney disease is a particularly common cause because the kidneys produce a hormone that signals your bone marrow to make red blood cells. When the kidneys are damaged, that signal weakens, and production drops.
Less commonly, low hemoglobin results from bone marrow problems, inherited conditions like sickle cell disease or thalassemia, or medications that suppress blood cell production.
How Your Doctor Figures Out the Cause
A low hemoglobin number on its own doesn’t tell you why it’s low. Your doctor will typically order additional blood tests to narrow things down. One of the most useful is ferritin, a protein that reflects your body’s iron stores. A ferritin level below 30 micrograms per liter generally confirms iron deficiency. The WHO uses a stricter cutoff of below 15 for definitive deficiency, but most clinicians treat anything under 30 as meaningful.
There’s a wrinkle, though. Ferritin rises during inflammation, so someone with a chronic inflammatory condition could have a ferritin of 80 and still be iron-deficient. For these patients, the diagnostic threshold is raised to 100 micrograms per liter, and doctors use additional markers like transferrin saturation to get a clearer picture.
Beyond iron studies, the size and shape of your red blood cells offer clues. Small cells typically point to iron deficiency, while unusually large cells suggest B12 or folate deficiency. Your doctor may also check kidney function, look for signs of chronic disease, or in some cases order a bone marrow evaluation.
Raising Your Hemoglobin Through Diet
If iron deficiency is the cause, dietary changes can make a real difference, especially for mild cases. Iron from food comes in two forms: heme iron from animal sources and non-heme iron from plants. Heme iron, found in red meat, poultry, and fish, is absorbed much more efficiently. Non-heme iron, found in beans, lentils, spinach, nuts, and fortified grains, is harder for your body to use but still valuable.
What you eat alongside iron-rich foods matters just as much as the foods themselves. Vitamin C dramatically improves absorption of non-heme iron by converting it into a form your intestinal cells can actually take up. Pairing a spinach salad with bell peppers or squeezing lemon over lentils makes a practical difference. Eating meat alongside plant-based iron sources also boosts absorption.
On the flip side, several common substances block iron absorption. Calcium competes with iron for absorption and is unique in that it inhibits both heme and non-heme iron. Compounds called phytates, found in whole grains, legumes, and seeds, bind to iron and reduce its availability. Polyphenols in tea, coffee, and red wine do the same. Egg protein also appears to inhibit absorption. If you’re trying to rebuild your iron stores, spacing your coffee or tea away from meals and avoiding calcium supplements at the same time as iron-rich foods can help.
Iron Supplements and What to Expect
For moderate deficiency or when diet alone isn’t enough, your doctor will likely recommend an oral iron supplement. Traditional guidelines suggest 150 to 200 mg of elemental iron per day, split into multiple doses. However, newer research suggests that alternate-day dosing of 60 to 120 mg, taken in the morning with vitamin C, may actually work better. Your body’s absorption mechanism resets roughly every 24 hours, so taking iron every other day can improve the percentage you absorb while reducing side effects.
Side effects are the main challenge with iron supplements. Constipation, nausea, and stomach cramps are common and are the reason many people stop taking them. Taking supplements on an alternate-day schedule, with food if needed (though an empty stomach improves absorption), can help. It typically takes two to three months of consistent supplementation to meaningfully raise hemoglobin levels, and another three to six months beyond that to fully replenish your body’s iron stores.
If oral iron doesn’t work, whether due to poor absorption, intolerance, or an underlying condition, intravenous iron is an option that bypasses the gut entirely and replenishes stores faster.
When Low Hemoglobin Needs Urgent Attention
Mild anemia is common and rarely dangerous on its own. But certain symptoms signal that your body is struggling to compensate. Chest pain, severe shortness of breath, or difficulty breathing at rest are signs of significant cardiovascular strain and warrant a trip to the emergency room. Feeling faint or nearly passing out, especially when standing, also suggests your hemoglobin may have dropped to a level your body can’t safely manage.
A hemoglobin below 8.0 g/dL is considered severe in most adults and often requires more aggressive treatment, potentially including a blood transfusion. If your levels are dropping rapidly rather than chronically low, that’s especially concerning because it suggests active bleeding or rapid destruction of red blood cells, both of which need immediate evaluation.