[1] Univ Surrey, Dept Nutr Sci, Guildford GU2 5XH, Surrey, England
[2] Univ Sheffield, Bone Biochem Lab, Dept Human Metab, Sheffield, S Yorkshire, England
[3] Newcastle Univ, Sch Agr Food & Rural Dev, Newcastle Upon Tyne NE1 7RU, Tyne & Wear, England
[4] Manchester Royal Infirm, Specialist Assay Lab Vitamin D, Manchester M13 9WL, Lancs, England
[5] Manchester Royal Infirm, Manchester Acad Hlth Sci Ctr, Manchester M13 9WL, Lancs, England
[6] Univ Surrey, Surrey Clin Res Ctr, Guildford GU2 5XH, Surrey, England