Final answer:
Individuals in the 1800s were often mistakenly committed to mental institutions due to undiagnosed pellagra, a disease caused by a deficiency in Vitamin B3 (niacin), which resulted in dementia-like symptoms.
Step-by-step explanation:
Many people were likely locked up in mental institutions in the 1800s unknowingly due to deficiencies in Vitamin B3 (niacin), which led to a disease known as pellagra. Pellagra was characterized by dementia, dermatitis, and diarrhea, and because the symptoms could be severe and resemble mental illness, individuals with pellagra were sometimes mistakenly admitted to mental institutions. The recognition and understanding of vitamins, including niacin, were the foundation for improving public health and influenced efforts to reform prisons and asylums.