Ilsa Katz was 85 when her daughter, Vivian Atkins, first noticed that her mother was becoming increasingly confused.

“She couldn’t remember names, where she’d been or what she’d done that day,” Ms. Atkins recalled in an interview. “Initially, I was not too worried. I thought it was part of normal aging. But over time, the confusion and memory problems became more severe and more frequent.”

Her mother couldn’t remember the names of close relatives or what day it was. She thought she was going to work or needed to go downtown, which she never did. And she was often agitated.

A workup at a memory clinic resulted in a diagnosis of early Alzheimer’s disease, and Ms. Katz was prescribed Aricept, which Ms. Atkins said seemed to make matters worse. But the clinic also tested Ms. Katz’s blood level of vitamin B12. It was well below normal, and her doctor thought that could be contributing to her symptoms.