Final answer:
Pellagra is caused by a deficiency in niacin (vitamin B3) and is marked by symptoms including dermatitis, diarrhea, dementia, and if untreated, death.
Step-by-step explanation:
Pellagra is a deficiency disease caused by a lack of niacin, also known as vitamin B3. This condition is characterized by the "3 Ds": Dermatitis, Diarrhoea and Dementia, which include symptoms such as headache, forgetfulness, depression, and anxiety. If not treated, it can result in a 4th 'D', Death. Pellagra is one of several deficiency diseases which highlight the importance of a balanced diet that includes essential nutrients. Other deficiency diseases mentioned are related to the lack of different vitamins, such as vitamin B6, vitamin B12 and folate, and thiamine, each causing various clinical disorders if not present in adequate amounts in one's diet.