Proton pump inhibitors, a frequently prescribed medication in older adults, impair absorption of vitamin B12 from food.

The major source of vitamin B12 is sunlight, and older adults are less likely to be outdoors and absorb vitamin B12 in this manner.

Vegetarian diets increase the risk of vitamin B12 deficiency.

Most older adults do not consume five servings of fruits and vegetables daily, which is the main dietary source of vitamin B12.

Normal age-related changes in the stomach include a lower production of gastric acid making vitamin B12 absorption less efficient.