What do researchers think is one cause of memory impairment related to growing older

Vitamin B12 deficiency.

Explanation:

Vitamin B12 protects the neurons and is vital to healthy brain functioning. In fact, a lack of B12 can cause permanent damage to the brain. Older people have a slower nutritional absorption rate, which can make it difficult for you to get the B12 your mind and body need. If aging adults address a vitamin B12 deficiency early, the memory loss could be reversed. Treatment is available in the form of a monthly injection.