Vitamin D insufficiency in a population of healthy western Canadians.
BACKGROUND
People with low levels of vitamin D and its metabolites are at increased risk for osteoporotic fractures. We wished to ascertain levels of vitamin D in a representative sample of adult western Canadians, to help assess the level of risk. We evaluated the prevalence of vitamin D insufficiency, defined as 25-hydroxyvitamin D [25(OH)D] less than 40 nmol/L, and seasonal variations in 25(OH)D, parathyroid hormone and related biochemical indices in a community-dwelling population of healthy Canadians living in Calgary (latitude 51 degrees 07'N).


METHODS
During calendar year 1999, we collected fasting overnight blood samples every 3 months from 60 men and 128 women (age range 27 to 89 years) who had volunteered to participate in another study. We used commercial radioimmunoassay kits to measure calciotrophic hormones and other biochemical indices. Regression models for longitudinal data were used to assess the effect of season and other potential predictors on individual parameters.


RESULTS
For a total of 64 participants (34%), vitamin D insufficiency, defined as 25(OH)D less than 40 nmol/L, was recorded at least once out of the 4 sampling times. After adjustment for age, body mass index and holiday travel, we observed the anticipated rise in serum 25(OH)D from a mean of 57.3 (standard deviation [SD] 21.3) nmol/L in the winter to 62.9 (SD 28.8) nmol/L in spring (p = 0.001) and 71.6 (SD 23.6) nmol/L in summer (p < 0.001), with a subsequent decline to 52.9 (SD 17.2) nmol/L in the fall (p = 0.008). The anticipated inverse relation between 25(OH)D and parathyroid hormone was not consistently observed: after adjustment for age, sex, body mass index and serum calcium, serum levels of parathyroid hormone did decrease significantly, from 39.5 (SD 18.8) ng/L in winter to 36.3 (SD 17.8) ng/L in summer (p = 0.001), but they continued to decline to 34.5 (SD 17.3) ng/L in the fall (p < 0.001). There was no association between 25(OH)D and parathyroid hormone (p = 0.21).


CONCLUSIONS
We documented a high prevalence of vitamin D insufficiency, which warrants consideration of dietary vitamin D supplementation.
Rucker
Diana
D
Department of Medical Science, University of Calgary, Alta.
Allan
Jane A
JA
Fick
Gordon H
GH
Hanley
David A
DA
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000416:Alberta / Q000453:epidemiology; D015415:Biomarkers; D005260:Female; D006801:Humans; D006887:Hydroxycholecalciferols / Q000097:blood; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood; D015995:Prevalence; D012044:Regression Analysis; D012307:Risk Factors; D012621:Seasons; D014808:Vitamin D Deficiency / Q000453:epidemiology* / Q000517:prevention & control
D015415:Biomarkers; D006887:Hydroxycholecalciferols; D010281:Parathyroid Hormone