Low wintertime vitamin D levels in a sample of healthy young adults of diverse ancestry living in the Toronto area: associations with vitamin D intake and skin pigmentation

Background: Vitamin D plays a critical role in bone metabolism and many cellular and immunological processes. Recent research indicates that concentrations of serum 25-hydroxyvitamin D [25(OH) D], the main indicator of vitamin D status, should be in excess of 75 nmol/L. Low levels of 25(OH) D have been associated with several chronic and infectious diseases. Previous studies have reported that many otherwise healthy adults of European ancestry living in Canada have low vitamin D concentrations during the wintertime. However, those of non-European ancestry are at a higher risk of having low vitamin D levels. The main goal of this study was to examine the vitamin D status and vitamin D intake of young Canadian adults of diverse ancestry during the winter months. Methods: One hundred and seven (107) healthy young adults self-reporting their ancestry were recruited for this study. Each participant was tested for serum 25(OH) D concentrations and related biochemistry, skin pigmentation indices and basic anthropometric measures. A seven-day food diary was used to assess their vitamin D intake. An ANOVA was used to test for significant differences in the variables among groups of different ancestry. Linear regression was employed to assess the impact of relevant variables on serum 25(OH) D concentrations. Results: More than 93% of the total sample had concentrations below 75 nmol/L. Almost three-quarters of the subjects had concentrations below 50 nmol/L. There were significant differences in serum 25(OH) D levels (p < 0.001) and vitamin D intake (p = 0.034) between population groups. Only the European group had a mean vitamin D intake exceeding the current Recommended Adequate Intake (RAI = 200 IU/day). Total vitamin D intake (from diet and supplements) was significantly associated with 25(OH) D levels ( p < 0.001). Skin pigmentation, assessed by measuring skin melanin content, showed an inverse relationship with serum 25(OH)D (p = 0.033). Conclusion: We observe that low vitamin D levels are more prevalent in our sample of young healthy adults than previously reported, particularly amongst those of non-European ancestry. Major factors influencing 25( OH) D levels were vitamin D intake and skin pigmentation. These data suggest a need to increase vitamin D intake either through improved fortification and/or supplementation.