Anemia

What Is Anemia?

Anemia is a condition characterized by an insufficient number of healthy red blood cells or inadequate hemoglobin concentration to meet the body's oxygen transport needs. Hemoglobin, the iron-containing protein in red blood cells, binds oxygen in the lungs and releases it to tissues throughout the body. When hemoglobin levels fall below threshold values — below 13 g/dL in adult men and below 12 g/dL in adult women, per the World Health Organization — the condition is classified as anemia.

Anemia affects approximately 1.62 billion people globally, representing roughly 25% of the world population. It is most prevalent among preschool-age children, pregnant women, and women of reproductive age. Symptoms typically include fatigue, weakness, pallor, shortness of breath on exertion, cold hands and feet, and difficulty concentrating.

Types and Nutritional Causes

While anemia has many causes — including chronic disease, genetic conditions (sickle cell anemia, thalassemia), and bone marrow disorders — nutritional deficiencies account for the majority of cases worldwide:

• Iron-deficiency anemia: the most common form globally; results from inadequate intake, poor absorption, increased demand (growth, pregnancy), or blood loss. Produces characteristic small, pale (microcytic, hypochromic) red blood cells.
• Vitamin B12 deficiency anemia: causes large, immature red blood cells (megaloblastic anemia); common in strict vegans, older adults with reduced gastric acid, and those with pernicious anemia.
• Folate deficiency anemia: also megaloblastic; frequently seen in pregnancy, alcoholism, and malabsorptive conditions.
• Vitamin A deficiency: impairs mobilization of iron from stores and suppresses red blood cell production.

Dietary Prevention and Management

For iron-deficiency anemia, dietary iron intake and absorption are both critical. Heme iron, found in red meat, poultry, and seafood, is absorbed at 15–35% efficiency regardless of dietary context. Non-heme iron, from legumes, fortified cereals, tofu, dark leafy greens, and seeds, is absorbed at only 2–20% but absorption is substantially enhanced by simultaneous consumption of vitamin C — 50 mg of vitamin C can increase non-heme iron absorption by up to six-fold. Conversely, tannins in tea and coffee, phytates in unsoaked legumes and whole grains, and calcium supplements inhibit non-heme iron absorption when consumed in the same meal. Cooking in cast iron cookware can meaningfully increase the iron content of acidic foods. For B12 deficiency, vegans and strict vegetarians require either fortified foods or supplements (2.4 mcg per day); absorption of high-dose oral supplements (1,000 mcg) occurs through passive diffusion independent of intrinsic factor, making this an effective management strategy even in pernicious anemia.