The purpose of this study is to investigate whether a supplement of 25-hydroxyvitamin D is five-times more potent in raising vitamin D status (as reflected by serum 25(OH)D) compared to an equivalent amount of vitamin D3 in older adults. It will entail a 10 week supplementation study during winter months.

The UK (McCance & Widdowson) food composition tables suggests that 25-hydroxyvitamin D (which is present in some foods, albeit at very low concentrations, but which is also commercially available) may possess up to 5-times the activity of native vitamin D3 in food. Thus, in theory, each micogram of 25-hydroxyvitamin D consumed in the diet could boost vitamin D status up to five times most effectively compared to each microgram of native vitamin D in food. It is worth noting, however, that estimates of potency range from 2 to 5, depending on approach used, and that the real potency needs to be confirmed in a human study. This study aims to examine the biological activity of 25-hydroxyvitamin D (i.e., its potency relative to vitamin D3) as well as its effect on selected functional markers in a randomised, double-blind, human intervention trial in older adults.

Inclusion Criteria:

• Subjects will be eligible if they are 45+ years of age
• Body Mass Index (BMI) 19-30

Exclusion Criteria:

• have hypercalcaemia
• chronic illness
• renal or liver disorders
• taking medications that might interact with vitamin D or metabolite
• drank more than > 21 standards (male)/ 14 standards (female) of alcohol per week
• planning to change smoking habits