Vitamin D status of women in the Geelong Osteoporosis Study: association with diet and casual exposure to sunlight.
OBJECTIVE
To assess vitamin D intake and casual exposure to sunshine in relation to serum 25-hydroxyvitamin D (25OHD) levels.


METHODS
Cross-sectional study of a population-based, random sample of women aged 20-92 years, assessed between 1994 and 1997.


METHODS
861 women from the Barwon Statistical Division (population, 218000), which includes the city of Geelong (latitude 38 degrees south) in Victoria.


METHODS
Vitamin D intake; serum 25OHD level; season of assessment; exposure to sunshine.


RESULTS
Median intake of vitamin D was 1.2 microg/day (range, 0.0-11.4 microg/day). Vitamin D supplements, taken by 7.9% of participants, increased intake by 8.1% to 1.3 microg/day (range, 0.0-101.2 microg/day) (P< 0.001). A dose-response relationship in serum 25OHD levels was observed for sunbathing frequency before and after adjusting for age (P< 0.05). During winter (May-October), serum 25OHD levels were dependent on vitamin D intake (partial r2= 0.01; P<0.05) and were lower than during summer (November-April) (age-adjusted mean, 59nmol/L [95% Cl, 57-62] v 81 nmol/L [95% CI, 78-84]; P<0.05). No association was detected between serum 25OHD and vitamin D intake during summer. The prevalences of low concentrations of serum 25OHD were, for <28nmol/L, 7.2% and 11.3% overall and in winter, respectively; and, for <50 nmol/L, 30.0% and 43.2% overall and in winter, respectively.


CONCLUSIONS
At latitude 38 degrees south, the contribution of vitamin D from dietary sources appears to be insignificant during summer. However, during winter vitamin D status is influenced by dietary intake. Australia has no recommended dietary intake (RDI) for vitamin D, in the belief that adequate vitamin D can be obtained from solar irradiation alone. Our results suggest that an RDI may be needed.
Pasco
J A
JA
The University of Melbourne, Department of Clinical and Biomedical Sciences--Barwon Health, The Geelong Hospital, VIC.
Henry
M J
MJ
Nicholson
G C
GC
Sanders
K M
KM
Kotowicz
M A
MA
D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001315:Australia; D003430:Cross-Sectional Studies; D019587:Dietary Supplements; D005260:Female; D006801:Humans; D008875:Middle Aged; D015999:Multivariate Analysis; D010024:Osteoporosis / Q000503:physiopathology* / Q000517:prevention & control*; D011159:Population Surveillance; D011336:Probability; D012044:Regression Analysis; D018570:Risk Assessment; D012494:Sampling Studies; D012621:Seasons; D012680:Sensitivity and Specificity; D013472:Sunlight; D014807:Vitamin D / Q000008:administration & dosage* / Q000097:blood*
D014807:Vitamin D