Study cohorts. The figure provides examples of designs for examining the effects of vitamin D fortification on development of diseases for a follow-up period of up to 50ὕyears. The birth (grey boxes with allowance for short “wash-out period” in between) and follow-up years (arrows) of individuals from subgroups exposed before and after birth are given in relation to initiation or termination of vitamin D fortification.
Jacobsen et al. BMC Public Health 2013 13:515 doi:10.1186/1471-2458-13-515