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

Abstract

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.