Anaemia, sometimes known as blood deficiency, is defined as a condition in which the concentration of haemoglobin is below the level that is normal for a given individual. It is associated with a group of diseases whose primary characteristic is a reduction in the (1) amount of haemoglobin in the red blood cells (erythrocytes), and/or (2) the number of erythrocytes per unit volume of blood (for a person of a given age and sex), and/or (3) the total amount of blood in the organism. In any community in which anaemia is prevalent, the distribution of haemoglobin concentrations in anaemic persons overlaps that for persons with normal haemoglobin concentration.
Nutritional anaemia results from a deficiency in one or more essential nutrients, regardless of the cause of the deficiency. Anaemia can also be caused by parasitic diseases, the two chief culprits being intestinal parasites and malaria.
Anaemia causes pathological changes which result from disruption of the organism's oxygen supply; the degree of manifestation dependent upon the degree of anaemia and its developmental speed. The most important general symptoms of anaemia are weakness, pale skin colour, shortness of breath, dizziness, and a tendency to faint; the primary causes are loss of blood, impairment of blood formation, and increased destruction of blood.
Anaemia is a frequent result of pregnancy and childbirth and as such is a prominent problem in developing countries where high-frequency pregnancies are standard.
In some parts of rural Africa, where women may expend as much as 85% of their daily energy intake fetching water, incidence and severity of anaemia increases during the dry season, when up to 63% of pregnant women and 40% of non-pregnant women are anaemic.