Vitamin D and Health

UV doses effective for pre-vitamin D synthesis
(Jm -2 )
Seasonal variation in serum 25(OH)D concentration
3.19 The main factor affecting skin synthesis is availability of UVB radiation (Webb & Engelsen, 2006).
There is a well-observed seasonal cycle in serum/plasma 25(OH)D concentrations in the UK and other
countries at mid-high latitudes (Poskitt et al., 1979; Beadle et al., 1980; Livesey et al., 2007) which
relates to the greater UVB content of solar UVR in summer.
3.20 During winter, the small amount of UVB in sunlight is insufficient to initiate synthesis of any
biologically relevant quantities of vitamin D (Webb et al., 1988; Webb et al., 1989). In the UK,
sunlight-induced vitamin D synthesis in the white-skinned populations becomes effective from April.
Maximum serum 25(OH)D concentrations are observed in September after a summer of exposure,
followed by a decline from October onwards through the winter months until the following spring.
(Webb et al., 2010) measured serum 25(OH)D concentrations of white adults (n=125; age, 20-60 y)
every month over 1 year and reported that mean concentration was highest in September (71 nmol/L)
and lowest in February (46 nmol/L).
3.21 A seasonal difference in serum/plasma 25(OH)D concentration of the UK population has also been
observed in national surveys (see chapter 8). Figure 6 shows the estimated monthly average UV doses
(Jm -2 ) effective for pre-vitamin D synthesis in the UK from 2008-2012.
3.22 The metabolic implications of seasonal variation in serum 25(OH)D concentration are currently
unknown.
FIGURE 6: The modelled monthly averaged UV doses (Jm -2 ) effective for pre-vitamin D
synthesis in the UK from 2008-2012. (Courtesy of O’Neill, Kazantzidis, Webb, Cashman, EU ODIN
Project 28 )
6000
5000
4000
3000
2000
1000
0
Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
Month
28 This work was based on original model development funded by UK Department of Health.
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