The high prevalence of vitamin D insufficiency across Australian populations is only partly explained by season and latitude.
BACKGROUND
Inadequate sun exposure and dietary vitamin D intake can result in vitamin D insufficiency. However, limited data are available on actual vitamin D status and predictors in healthy individuals in different regions and by season.


METHODS
We compared vitamin D status [25-hydroxyvitamin D; 25(OH)D] in people < 60 years of age using data from cross-sectional studies of three regions across Australia: southeast Queensland (27 degrees S; 167 females and 211 males), Geelong region (38 degrees S; 561 females), and Tasmania (43 degrees S; 432 females and 298 males).


RESULTS
The prevalence of vitamin D insufficiency (<or= 50 nmol/L) in women in winter/spring was 40.5% in southeast Queensland, 37.4% in the Geelong region, and 67.3% in Tasmania. Season, simulated maximum daily duration of vitamin D synthesis, and vitamin D effective daily dose each explained around 14% of the variation in 25(OH)D. Although latitude explained only 3.9% of the variation, a decrease in average 25(OH)D of 1.0 (95% confidence interval, 0.7-1.3) nmol/L for every degree increase in latitude may be clinically relevant. In some months, we found a high insufficiency or even deficiency when sun exposure protection would be recommended on the basis of the simulated ultraviolet index.


CONCLUSIONS
Vitamin D insufficiency is common over a wide latitude range in Australia. Season appears to be more important than latitude, but both accounted for less than one-fifth of the variation in serum 25(OH)D levels, highlighting the importance of behavioral factors. Current sun exposure guidelines do not seem to fully prevent vitamin D insufficiency, and consideration should be given to their modification or to pursuing other means to achieve vitamin D adequacy.
van der Mei
Ingrid A F
IA
Menzies Research Institute, University of Tasmania, Hobart, Australia. Ingrid.vanderMei@utas.edu.au
Ponsonby
Anne-Louise
AL
Engelsen
Ola
O
Pasco
Julie A
JA
McGrath
John J
JJ
Eyles
Daryl W
DW
Blizzard
Leigh
L
Dwyer
Terence
T
Lucas
Robyn
R
Jones
Graeme
G
D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D011793:Queensland / Q000453:epidemiology; D012621:Seasons; D012867:Skin / Q000378:metabolism; D013472:Sunlight; D013648:Tasmania / Q000453:epidemiology; D014807:Vitamin D / Q000031:analogs & derivatives / Q000097:blood / Q000378:metabolism; D014808:Vitamin D Deficiency / Q000097:blood / Q000453:epidemiology*
D014807:Vitamin D; C104450:25-hydroxyvitamin D