Browsing by Author "Pajula, Elina"

Vitamin D is an essential vitamin linked especially to bone health. There are two biologically active forms of vitamin D: Cholecalciferol (vitamin D3) and ergocalciferol (vitamin D2). Although cholecalciferol is synthetized endogenously in the skin by sun light, it is not always enough to maintain sufficient vitamin D levels. For example, living on high latitudes, ageing and dark skin increase the risk for insufficient vitamin D status. Also, natural dietary sources of vitamin D are limited. This is why different fortification policies have been introduced. Fungi produce a unique sterol, ergosterol, which is converted into ergocalciferol when exposed to UVB irradiation. UVB-irradiated yeasts and mushrooms have been studied for their potential to provide an affordable and non-animal origin alternative for vitamin D3 supplementation. In this thesis, UVB-treated, vitamin D2 -rich baker´s yeast (Saccharomyces cerevisiae) was used to enrich the rat diets. The aim was to study the bioavailability and safety of the yeasts and compare them to D2 and D3 supplements. Two different forms of yeast were used: The whole irradiated and dried yeast cells (vitamin D2 -rich yeast) and the cell wall fraction of the same yeast (yeast cell walls). Both yeasts were tested with two different doses: 375 µg/kg and 750 µg/kg. The positive control diets contained vitamin D3 and D2 from the supplements and the same test doses were used. Further, there was control diet containing the recommended amount of vitamin D3 for rats, 25 µg/kg. 54 Sprague-Dawley female rats were divided into groups of six, each group receiving a different diet The experiment period was eight weeks after which the rats were sacrificed for serum 25(OH)D, 3-epi-25(OH)D, calcium, phosphorus and intact PTH analyses, as well as BMD, BMC and bone area measurements. The results were analysed for statistical significance with one-way analysis of variance (ANOVA) and correlations between the variables with Pearson´s two-tailed correlation test. The bioavailability and safety were evaluated based on the results.