Tj. Hine et Nb. Roberts, SEASONAL-VARIATION IN SERUM 25-HYDROXY VITAMIN-D-3 DOES NOT AFFECT 1,25-DIHYDROXY VITAMIN-D, Annals of clinical biochemistry, 31, 1994, pp. 31-34
The seasonal variation of serum 25-hydroxy vitamin D-3 and 1,25-dihydr
oxy-vitamin D has been investigated. Blood was taken from 27 healthy v
olunteers, aged 21-44 years old at 3 monthly intervals over a period o
f 1 year. A scrolling monthly programme with 12 quarterly (3 month) ti
me periods was developed. A summer associated increase in 25-hydroxy v
itamin D-3 was significantly correlated with but lagged behind by 2 mo
nths, the increase in recorded sunlight hours. However, four individua
ls showed no seasonal rise but maintained constant concentrations thro
ughout the year within the established reference range. Serum 1,25-dih
ydroxy vitamin D showed marked intra-individual variability with no se
asonal pattern although the highest concentration (180 pmol/L) was obs
erved in the winter and no concentration greater than 108 pmol/L in th
e summer.