Final answer:
The deficiency of niacin, also known as Vitamin B3, is known for the '4 Ds': dermatitis, dementia, diarrhea, and death. This condition is called pellagra, which can be fatal if not treated.
Step-by-step explanation:
The classic vitamin deficiency known for the '4 Ds,' which are dermatitis, dementia, diarrhea, and death, is a deficiency of niacin (Vitamin B3). This condition, characterized by these symptoms, is called pellagra. If pellagra is not treated, it can indeed lead to the fourth 'D,' which is death.
Niacin is crucial for many metabolic processes in the body and is found in various foods such as meat, fish, poultry, and whole grains. Ensuring a balanced diet with adequate niacin is essential for preventing pellagra and maintaining overall health.