Circulating levels of 25-hydroxyvitamin D [25(OH)D)] have been established as the biomarker for vitamin D status, and are representative of the sum total of dietary, supplementary and endogenously produced vitamin D. Generally, a plasma level of 25(OH)D below 25nmols/L will result in a severe deficiency of vitamin D and lead to the traditional deficiency diseses of osteomalacia in adults and rickets in children (figure 1). Plasma concentrations of 25(OH)D between 25 and 40nmols/L are likely to lead to chronic insufficiency and can increase the risk of developing a number of disease such as cardiovascular disease, diabetes, metabolic syndrome and cancer. Research consistently shows that large numbers of people in Western nations have insufficient vitamin D status with plasma levels below 40nmol/L. Generally, older individuals and those with darker skin, living in higher latitude areas are susceptible to vitamin D deficiency during winter months.
Figure 1. Table to show the ranges of vitamin D with established risks.
A study performed in Canada investigated the 25(OH)D concentration and dietary intakes of 5306 individuals. Dietary intake was assessed by an interview with the subjects, and plasma concentrations of 25(OH)D were assessed by blood sample and compared supplement users and non-users between season and race. The results showed that 5.4% of individuals had 25(OH)D levels below 30nmol/L, 12.7% had levels below 40nmol/L, and 25.7% had levels below 50nmols/L. Twenty percent of the subjects were white, and those individuals had higher 25(OH)D concentrations when compared to non-white individuals. For example, less than 5% of white Canadians had year round levels below 30nmol/L whereas for non-white Canadians the prevalence was 16.3%. Likewise, only 8.7% of white Canadians had year round 25(OH)D levels below 40nmol/L whereas the prevalence in non-white Canadians was 30.5%. One quarter of the subjects investigated did not meet the Canadian RDA for vitamin D intake.
Forty subjects had vitamin D levels over 150nmol/L and of these 46.7% were taking a vitamin D supplement. In the years 2007 to 2009 31% of subjects in the study reported taking a vitamin D supplement, with approximately 95% of supplements being in the vitamin D3 form. Overall, supplement users had higher levels of winter 25(OH)D, but the benefit of supplements was less apparent in summer as would be expected. Non-supplement users had twice the prevalence of deficiency and insufficiency than did supplement users, suggesting that supplements of vitamin D are effective at raising plasma levels on 25(OH)D. These results support other studies that show that individuals who use vitamin D supplements have better vitamin D status, particularly those with darker skin in winter months. Supplement use in this study was associated with a 40-50% reduction in the risk of inadequate vitamin D status.
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