Being anemic means your blood doesn’t carry enough oxygen to your body’s tissues. This happens when you have too few red blood cells or your red blood cells don’t contain enough hemoglobin, the protein that binds oxygen. The World Health Organization defines anemia as hemoglobin below 12.0 g/dL in women and below 13.0 g/dL in men. It’s one of the most common blood conditions worldwide, and it ranges from mild and barely noticeable to severe enough to affect your heart and brain.
How Anemia Feels
Mild anemia often creeps in so gradually that you don’t realize anything is wrong. The earliest signs tend to be vague: you feel tired all the time, your muscles feel weak, and tasks that used to be easy leave you winded. Because these symptoms overlap with so many other things, including poor sleep, stress, or just being busy, many people chalk it up to normal life.
As hemoglobin drops further, the symptoms sharpen. You might notice shortness of breath during exercise, dizziness when you stand up quickly, or chest tightness. When hemoglobin falls below about 9 g/dL, visible changes appear: the inside of your lower eyelids looks pale instead of pink, your nail beds lose color, and the creases of your palms may look unusually light. Some people develop headaches, cold hands and feet, or a heart that feels like it’s racing even at rest, because the heart has to pump harder to move oxygen-poor blood through the body.
Iron Deficiency: The Most Common Cause
Iron is the raw material your body uses to build hemoglobin. When iron runs low, hemoglobin production slows and your red blood cells shrink. This is iron deficiency anemia, and it accounts for the largest share of anemia cases globally.
The reasons people become iron deficient fall into a few categories. Blood loss is a major one: heavy menstrual periods, ulcers, or even frequent blood donation can drain iron faster than your diet replaces it. Poor absorption is another. People who’ve had bariatric surgery, those with celiac disease or inflammatory bowel disease, and people who regularly take acid-reducing medications all absorb iron less efficiently. Even drinking coffee, tea, or taking calcium supplements with meals can reduce how much iron your gut pulls in.
Diet matters too. Vegetarian and vegan diets can provide plenty of iron, but the type of iron in plants (non-heme iron) is absorbed at roughly 17% or less, compared to about 25% for the heme iron found in meat, poultry, and seafood. In Western diets, heme iron makes up only 10% to 15% of total iron intake yet contributes around 40% of what the body actually absorbs. That gap explains why people eating plant-based diets need to be more intentional about iron-rich foods like lentils, spinach, fortified grains, nuts, and seeds, ideally paired with vitamin C to boost absorption.
Vitamin B12 and Folate Deficiency
Iron isn’t the only nutrient involved. Your body also needs vitamin B12 and folate to produce red blood cells that are the right size and shape. Without enough of these vitamins, the body makes red blood cells that are too large and don’t function properly, so they’re less able to carry oxygen.
B12 deficiency causes a distinct set of symptoms beyond the usual fatigue. You may feel numbness or tingling in your hands and feet, have trouble with balance, or notice changes in memory and thinking. Left untreated, B12 deficiency can cause lasting nerve damage in the brain and spinal cord. This type of anemia is more common in older adults (who absorb B12 less efficiently), people with digestive conditions, and those who eat no animal products, since B12 occurs naturally only in animal-based foods.
Genetic Forms of Anemia
Some people are anemic because of how their hemoglobin is built, not because of a nutritional gap. Sickle cell disease is the most well-known example. A single gene mutation causes the body to produce an abnormal form of hemoglobin that, under low-oxygen conditions, forces red blood cells into a rigid, crescent shape. These sickle-shaped cells break apart easily and live only 10 to 20 days instead of the normal 120, creating a constant shortage. Beyond chronic anemia, the rigid cells can block small blood vessels and cause episodes of severe pain.
Thalassemia is another inherited condition where the body underproduces one of the protein chains that make up hemoglobin. Severity varies widely depending on the specific genetic combination. Some people carry a thalassemia trait and have only mild anemia, while others need regular medical management throughout life. When sickle cell and thalassemia genes are inherited together, the clinical picture can range from mild to as severe as full sickle cell disease.
Who Is Most at Risk
Certain groups face a significantly higher chance of becoming anemic. The WHO identifies the most vulnerable populations as children under five (especially infants under two), menstruating adolescent girls and women, and pregnant and postpartum women. Pregnancy increases iron demands dramatically, and insufficient iron during pregnancy raises the risk of premature birth and low birth weight.
Athletes in high-intensity sports are also at elevated risk due to higher iron needs, chronic low-grade inflammation, and increased losses through sweat and exertion. Older adults face a different set of risks: reduced nutrient absorption, chronic diseases that interfere with red blood cell production, and medications that can cause slow blood loss from the digestive tract.
How Anemia Is Diagnosed
A simple blood test measuring hemoglobin is the starting point. If your hemoglobin is below the threshold for your sex, additional tests help pinpoint the cause. Ferritin, which reflects your body’s iron reserves, is the most reliable marker for iron deficiency. Levels below 30 micrograms per liter generally confirm iron deficiency, though in people with chronic inflammation, the cutoff rises to 100 because inflammation artificially inflates ferritin numbers. In those cases, a second measurement called transferrin saturation (below 20%) helps clarify the picture. Serum iron levels on their own fluctuate too much throughout the day to be useful.
For suspected B12 or folate deficiency, blood work will show abnormally large red blood cells along with low vitamin levels. Genetic anemias are typically identified through specialized hemoglobin testing.
Treatment and What to Expect
Treatment depends entirely on what’s causing the anemia. For iron deficiency, oral iron supplements are the most common first step. Most adults need 150 to 200 mg of elemental iron per day, which typically means taking iron tablets once or twice daily. Iron supplements are best absorbed on an empty stomach with a source of vitamin C, though some people find they cause nausea or constipation and tolerate them better with food. It generally takes several weeks to feel a noticeable improvement, and three to six months to fully rebuild iron stores.
B12 deficiency is treated with B12 supplements, either taken by mouth or given as injections depending on whether the issue is dietary or an absorption problem. Folate deficiency responds to folate supplementation and dietary changes. In both cases, neurological symptoms like tingling or balance problems may improve slowly or, if the deficiency was prolonged, may not fully reverse.
Genetic anemias like sickle cell disease require ongoing management tailored to the severity of the condition. Mild inherited anemias sometimes need no treatment at all.
What Happens If Anemia Goes Untreated
Mild anemia that’s caught and corrected rarely causes lasting harm. But chronic, untreated anemia forces the heart to work harder to compensate for reduced oxygen delivery. Over time, this can lead to heart failure, abnormal heart rhythms, and angina. The brain is equally vulnerable: prolonged oxygen deprivation contributes to cognitive impairment, and in severe cases, organ damage can extend to the kidneys. For pregnant women, the stakes include premature delivery and babies born at dangerously low weights.
The good news is that most anemia is treatable once the cause is identified. Even people who’ve felt exhausted for months or years often see significant improvement within weeks of starting the right treatment.