Vitamin D deficiency in Northern Sweden

........................................................................................... iii Sammanfattning på svenska ............................................................. v Original papers ............................................................................... vii Abbreviations ................................................................................. viii Background ........................................................................................ 1 The history of vitamin D – a brief summary ................................................................... 1 Physiology ........................................................................................................................ 2 Dietary intake of vitamin D ............................................................................................. 4 Ultraviolet B radiation-induced vitamin D synthesis in the skin ................................... 5 Effects of latitude and season .......................................................................................... 6 Laboratory analyses of 25(OH)D .................................................................................... 6 Vitamin D and associated medical conditions ................................................................ 7 Definitions of vitamin D deficiency and sufficiency ...................................................... 11 Dietary intake reference values ...................................................................................... 13 Treatment of vitamin D deficiency ................................................................................ 14 Risk groups for vitamin D deficiency ............................................................................. 16 Epidemiology .................................................................................................................. 17 Depression and anxiety .................................................................................................. 18 Muscle strength .............................................................................................................. 19 The Vitamin D hypothesis – a summary ....................................................................... 21 Aims of the thesis ............................................................................ 22 Materials and Methods ................................................................... 23 Materials and methods Papers I III ............................................................................ 23 Study population and recruitment process ........................................................... 23 Data collection ......................................................................................................... 26 Lower limb muscle strength measurements .......................................................... 26 Grip strength measurements ................................................................................... 27 Analyses Paper I-III ................................................................................................ 28 Analysis of serum-25-hydroxyvitamin D .............................................................. 29 Materials and Methods Paper IV ................................................................................ 29 Study design ............................................................................................................ 29 Study population and recruitment process ............................................................ 31 Study protocol ......................................................................................................... 32 Data collection and analyses .................................................................................. 32 Statistics ......................................................................................................................... 33 Ethical considerations ....................................................................................................35