Final answer:
A patient with symptoms including dermatitis, diarrhea, and dementia (the three Ds) may have a deficiency in niacin (Vitamin B3).
Step-by-step explanation:
A patient with symptoms including dermatitis, diarrhea, and dementia (the three Ds) may have a deficiency in niacin (Vitamin B3). Pellagra is a deficiency disease of niacin and is characterized by the 3 Ds. If left untreated, it can lead to death.