Abstract
The US Institute of Medicine defined serum 25-hydroxyvitamin D (25OHD) cut point values of 30 nmol/L and 40 nmol/L were used to assess the vitamin D status of South Asian and European Canadians of self-identified ancestry living in the National Capital Region of Canada. Serum 25OHD values were measured in the spring and fall of 2012 to represent status during the winter and summer months, respectively. A total of 1238 measurements were obtained from 669 participants (49% South Asian ancestry): some participants were measured only once (spring or fall). Median 25OHD values were significantly higher in participants of European ancestry: 70.8 nmol/L (68.1, 73.5; 95% CI) versus South Asian ancestry: 42.7 nmol/L (40.5, 45.0; P<0.001). Spring vs. fall differences were small for each ethnic group and significant only for those of European ancestry (2.9, CI: 1.0–4.9 nmol/L; P = 0.01). Among participants of South Asian ancestry, 27.3% (fall) and 29.1% (spring) of females had values <40 nmol/L while the percentages for males were considerably higher (36.5% and 44.2%, respectively). The corresponding values for participants of European ancestry were ≤10%, showing that the South Asian participants were less likely to achieve the 25OHD concentrations established by the IOM for optimum bone health. Investigation of the factors related to serum 25OHD levels showed that supplement intake and ethnic background were associated with the biggest differences. Skin color was not a major factor, suggesting that genetic factors are responsible for the observed differences between participants of different ethnic backgrounds.
Highlights
Serum 25-hydroxyvitamin D (25OHD) levels currently represent the best biomarker for assessing vitamin D nutriture because they reflect ingested vitamin D as well as that derived from cutaneous synthesis [1]
Males of European ancestry had higher Body mass index (BMI) values but no difference was observed among participants of South Asian ancestry
An important finding of this study is that participants of South Asians ancestry were more likely than participants of European ancestry to fall short of the Institute of Medicine (IOM) recommended 25OHD levels for the prevention of deficiency and inadequacy that are based on bone health. 29–44% of South Asian participants had serum 25OHD
Summary
Serum 25-hydroxyvitamin D (25OHD) levels currently represent the best biomarker for assessing vitamin D nutriture because they reflect ingested vitamin D as well as that derived from cutaneous synthesis [1]. The IOM reported that at serum 25OHD 50 nmol/L, 97.5% of the population would be sufficient, corresponding to a recommended dietary allowance (RDA) of 600 IU/d for individuals 70 years of age and 800 IU/d for those above 70 years of age. These reference intake values assume minimal sun exposure. It is important to study individual groups given the many genetic factors that associate with vitamin D status [5, 6], including variations in skin color and reported vitamin D binding protein [7, 8] as well as dietary and sun exposure preferences. Comprehensive data are lacking for the Canadian population, except for a small study of South Asian and East Asian students from the University of Toronto [12] and a study of Non-Western immigrant children between the ages of 1–6 living in Toronto [13]
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