The answer

Deidre is correct in thinking that her mum is at risk of vitamin D deficiency. People aged over 65 years and those who are housebound or confined indoors for long periods of time are two of the 'at risk of vitamin D deficiency' groups listed by the National Institute for Health and Care Excellence (NICE) in its guidance on the topic. 

It would be sensible for Deidre to check whether her mum is already taking a supplement as she may well have been prescribed one as part of her assessment and treatment after her fall. The recommended daily dose for Deidre’s mum would be 10mcg, and it would be prescribed as ergocalciferol, calciferol or colecalciferol, or as part of a combined preparation, so she may not necessarily have noticed it in her patient notes.