Introduction
Involved in the regulation and expression of over 900 genes,1 vitamin D (VTD) has recently been recognized as an essential hormone required for innumerable physiological processes. Despite abundant evidence that VTD inadequacy is associated with widespread and assorted health problems including many cancers, heart disease, diabetes, infectious illnesses and autoimmune disorders,2, 3 numerous studies suggest an ongoing epidemic of VTD deficiency in Canada. With little risk and minimal cost, restoration of VTD adequacy with innovative public health interventions and low-cost supplementation may have the potential to ameliorate extensive suffering and dramatically improve the health and well-being of Canadians.
As ultraviolet B (UVB) rays from sunshine are the major source of VTD production in most people, various clinical studies show that high latitudes – where UVB sunlight intensity is too weak for extended periods to induce sufficient VTD skin synthesis for many people – have a major impact on VTD production. For example, reports in the literature suggest that 26.27% of Israelis (at 32°N), 57% of study participants in Boston (at 42°N) and 61–70% of Finns (at 64°N) have 25(OH)D levels lower than 37.5 nmol/l.4, 5, 6 Living at latitudes between 43° and 55°N, most Canadians are at high risk for VTD deficiency. This review was designed to assess the VTD status of the Canadian population as a whole.
There is ongoing discussion in the literature regarding optimal VTD status as measured by the main circulating metabolite, 25(OH)D. It has been known for some time, that 25(OH)D levels above 78 nmol/l are required to avoid increases of parathyroid hormone,7 and that absorption of calcium, magnesium and phosphate is maximized at values above 85 nmol/l.8 Levels of at least 90 nmol/l are suggested for genomic stability and prevention of cancer.9 With the existing state of knowledge, however, a cut-off value for VTD deficiency had previously been assigned as 75 nmol/l; a level that has been used in many studies. However, it has recently been suggested that ideal levels range from 100 to 150 nmol/l; values typically found in individuals with regular sun exposure living in sunny climates. Although toxicity is a distinct possibility with excessively high levels (above 250 nmol/l), the human body appears to have self-regulatory mechanisms to prevent toxicity, and thus the margin of safety is much higher than previously thought.10