It is known that low vitamin D status is a very common problem in the UK. It is also known that a lack of vitamin D availability has potentially serious health implications, especially with respect to bone and muscle function. Much research has recently taken place to establish the vitamin D requirements of key population groups (i.e. pregnant women, the elderly, ethnic minorities). However few data are available describing the vitamin D requirements for male and female adolescents. The period of adolescence is a key stage of growth and development - poor nutrition during this time can have detrimental health consequences for a lifetime.

No intervention studies have comprehensively investigated the vitamin D requirements of adolescents. The proposed ODIN Study will enable a better understanding of how adolescents respond to vitamin D supplementation and the most effective daily amount that will raise and maintain vitamin D status in adolescents during the winter-time. In addition, investigations into the mechanisms of action with respect to any differences observed across the doses of vitamin D and between the genders of the participants will also provide key information. Mechanisms of action will focus on genetic differences as well as differences in vitamin D metabolising enzymes.

The results obtained from this significant study will not only inform the European Food Standards Agency (EFSA) with respect to their imminent deliberations regarding vitamin D recommendations. The ODIN Study will also inform the UK Department of Health's Scientific Advisory Committee on Nutrition (SACN), the wider scientific community and be a critical resource for key stakeholders (i.e. food industry, government health agencies) to collaborate in determining future public health strategies, thus potentially positively impacting on the health of the population for years to come.

The investigators propose that the daily supplementation of 10µg/day (400 IU) and 20µg/day (800 IU) of vitamin D3 for five months will meet the vitamin D requirements of males and females aged 14-18 year and will be sufficient to maintain winter-time 25OHD levels above a range of thresholds between 30 and 50nmol/l.

Inclusion Criteria:

• Male or female
• Aged between 14 and 18 years
• Caucasian ethnicity
• In good health
• Written informed consent from the adolescent (and parent if required)

Exclusion Criteria:

• Currently receiving treatment for medical conditions likely to affect vitamin D metabolism
• Hypercalcaemia (>2.5mmol/l)
• Regular use of sun-beds
• Having a sun holiday one month prior to commencing the trial or plans for a sun holiday within the study period.
• Use of vitamin supplements containing vitamin D - if the prospective participant agrees to stop vitamin D supplementation to join the study, a wash-out period of 8 weeks prior to commencing the trial would be acceptable.
• Excessive consumption of alcohol (>14 units per week for females, >21 units per week for males)
• Smoking >10 cigarettes per day
• Those following a weight-reducing diet or under dietary restriction (except vegetarianism)
• Known intolerance/allergy to the constituent ingredients of the daily supplement
• Clinically significant haematological abnormalities other than mild anaemia (Hb<12.0g/dl)
• Active malignancy
• Pregnant or planning a pregnancy during the study period.
• Breast-feeding mothers