Final answer:
Excessive sunlight exposure is least likely to cause vitamin B12 deficiency in the elderly. The main causes are poor dietary intake, malabsorption, and decreased production in the stomach.
Step-by-step explanation:
Vitamin B12 deficiency in the elderly is least likely to occur from excessive sunlight exposure. The main causes of vitamin B12 deficiency in the elderly are poor dietary intake, malabsorption, and decreased production in the stomach. Poor dietary intake can be due to a lack of meat or other viable sources of vitamin B12, while malabsorption can result from conditions such as Crohn's disease or surgical removal of the intestines or stomach. Decreased production in the stomach can occur due to factors like weight loss surgeries or certain diseases. However, excessive sunlight exposure does not play a role in vitamin B12 deficiency.