Niacin

Function: Niacin is involved in many different body processes. It aids in the breakdown of fats and proteins and in red blood cell formation. Also important in reproduction.
Symptoms of Deficiency: A deficiency of niacin can cause pellagra. Signs of pellagra are inflammation of the tongue and mouth, as well as poor feathering and a scaly dermatitis of the feet and the head. Nervousness can also be observed.
Symptoms of Toxicity: While in people it can cause both the cholesterol and triglyceride levels to decrease, it can also cause the blood vessels to dilate. This may result in indigestion, itchy skin, liver damage, ulcers, and an increase in glucose. These problems are not always seen in birds.
Found: Niacin is found in all foods, but the highest amounts are in animal products. In plants, it is poorly absorbed. Rice polishings, as well as yeast, are rich sources of niacin. You can also find niacin in chicken, tuna, peanuts, sesame seeds, brewer's yeast, salmon, eggs, peas, and potatoes.

Reference: "The Healthy Bird Cookbook" by Robin Deutsch