Anemia/etiology; Deficiency Diseases/complications; Adolescent; Adult; Anemia/epidemiology; Anemia, Hypochromic/epidemiology; Anemia, Hypochromic/metabolism; Anemia, Hypochromic/prevention & control; Anemia, Megaloblastic/etiology; Anemia, Megaloblastic/prevention & control; Anemia, Pernicious/etiology; Asia; Child; Child, Preschool; Female; Folic Acid Deficiency/complications; Folic Acid Deficiency/epidemiology; Humans; Infant; Iron Deficiencies; Male; Middle Aged; Pregnancy; Pregnancy Complications/etiology; Sprue, Tropical/etiology; Tropical Climate; Vitamin B 12 Deficiency/complications; Vitamin B 12 Deficiency/epidemiology