Vitamin D is central in calcium turnover, and adequate levels are important for skeletal health. It is not clear how large contributions from food and sunlight are in Swedish primary care patients, considering the low radiation of UVB in Sweden and fortification of some foods, and whether differences exist between patients of immigrant and Swedish origin. Increasing incidence of osteoporosis-related fractures is a major global health problem. Genetic variations in metabolising enzymes and in the Vitamin D receptor (VDR) have also been shown to be of importance to the overall effect of vitamin D. Polymorphic variation in the gene CYP2R1 encoding the 25-hydroxylase has previously been reported to correlate with circulating levels of 25(OH)D3. Results of association studies between genetic variants of the VDR and muscle strength, as well as falls have been contradictory. The purposes of this thesis were to examine possible differences in plasma-25(OH)D3 levels and intake of vitamin D between Swedish and immigrant female primary care patients, to estimate what foods contribute the most, and to identify contributors to vitamin D status (Paper I-II). Furthermore, the relationship between polymorphisms in the CYP2R1 gene and levels of 25(OH)D3 as well as other biochemical parameters (parathyroid hormone, calcium, phosphate and fibroblast growth factor 23) of skeletal homeostasis, bone mineral density and incidence of fractures was investigated (Paper III). Also, the association between genetic variations in the gene for the vitamin D receptor and measures of muscle strength, physical performance and falls (Paper IV), was investigated by using data from a Swedish multicenter study of elderly men (MrOS). Most important results: Vitamin D deficiency was common, with significant difference between Swedish born and immigrant patients (Paper I). Food intake of vitamin D is associated with circulating vitamin D, but the factors most strongly affecting vitamin D levels were reported sun holiday and origin (Paper II). CYP2R1 polymorphisms are associated with circulating levels of 25(OH)D3 and bone mineral density (Paper III). VDR genetic variants do not appear to have a direct effect on muscle strength or physical performance and incidence of falls in elderly Swedish men (Paper IV).

Breast cancer is a world health problem and is a leading cause of cancer-related death among women in the United States. However, breast cancer risks were reported to be reduced through exposure to Vitamin D through its Receptors identified as the p53 target gene. The purpose of this study was to assess the associations between VDR gene polymorphisms knowledge/awareness and decisions to reduce breast cancer risks and likelihood of mammogram screening among women in Texas. Data from survey were used. Roy adaptation model was the theoretical framework that guided this quasi- experimental, quantitative research. The dependent variables were decisions to reduce breast cancer risks and likelihood of mammogram screening. The independent variables were knowledge about VDR gene polymorphisms and exposure to vitamin D. The covariates were level of education, awareness, lifestyle, breast self-exams, mammograms, age, early menarche, late menopause, and family history of breast cancer. The chi-square test and regression analysis were used to test the stated research hypotheses and to answer the research questions. Knowledge of VDR gene polymorphisms and exposure to vitamin D were not significantly associated with breast cancer risk, ï?£2 (3, N= 250) =3.84, p > 0.05. Also, awareness of the risk factors for breast cancer was not significantly associated with decisions to go for mammogram screenings or to enroll in breast cancer risk-reduction programs, ï?£2 (3, N= 250) =1.58, p > 0.05. To advocate for the promotion of awareness of the importance of pharmacogenetic testing for VDR gene polymorphisms for early detection of breast cancer, which would help to undertake appropriate therapeutic measures in a timely manner to prevent cancer metastasis, further research is warranted.