OASIS Study: Vitamin D Deficiency Prevention Among Older Adults in Ireland

This randomised controlled dietary intervention study aims to recruit 200 older adults (\>65 years) who will be randomised to receive vitamin D-fortified bread and advice to consume additional commercially available fortified foods (Treatment group) or identical unfortified bread and advice to consume additional commercially available fortified foods (Control group). The outcome of the study is to test whether increasing vitamin D intake through food (Treatment group) is sufficient to prevent wintertime vitamin D deficiency (measured using serum concentrations of 25-hydroxyvitamin D \<30 nmol/L) in comparison with the Control group. The target vitamin D intake for the treatment group in this study is \>15-20 μg/day vitamin D. This will maintain serum concentrations of 25-hydroxyvitamin D (25(OH)D) (the biomarker of vitamin D status) \> 30 nmol/L, the clinical deficiency threshold to prevent metabolic bone disease, in over 90% of participants. At this vitamin D intake level, about 80% of participants will have a 25(OH)D concentration \> 50 nmol/L, the personal intake target in the US and EU.