Niacin Deficiency
Niacin (nicotinic acid) is important in tissue respiration; and is needed for proper brain functions, the nervous system, and for a healthy skin.
The early symptoms of mild and moderate deficiencies are the same as the early symptoms of pellagra: suspicion, hostility, irritability, insomnia, loss of memory, and anxiety; abdominal pain, a burning sensation in the tongue; and dry and scaly patches where the skin is exposed to sunlight. As the deficiency becomes more severe, the nervous system symptoms progress to insanity; the digestive symptoms to diarrhea; the tongue becomes red and raw-looking, and the skin patches may become cracked and fissured.