Vitamin A is important for vision, gene expression, immunity, growth and development, and red blood cell production. Deficiency can cause blindness and increase risk of respiratory illness, diarrhea, and HIV transmission. Recommended daily intake varies by age, sex, and life stage. Sources include cod liver oil, fortified cereals, dairy, eggs, sweet potatoes and leafy greens. Both deficiency and toxicity can cause health issues, so intake levels need to be monitored.