Introduction: Vitamin D status is influenced by behavioural and dietary factors. The aim of this doctoral thesis was to determine vitamin D status and differences between premenopausal and postmenopausal Slovenian women aged 44 to 65 years and to develop a model for predicting vitamin D status without measuring serum levels.
Methods: A cross-sectional epidemiological study was conducted between 1 March and 31 May 2021 (during Covid-19 lockdown), involving 319 women aged 44 to 65 years. 176 participants were included in the final analysis. Vitamin D status was determined by measuring the concentration of total 25-hydroxyvitamin D (total 25(OH)D), vitamin D-binding protein (DBP), albumin and by calculating bioavailable and free 25(OH)D. For the fortification model calculations, the vitamin D contents of unenriched milk (including yoghurt) and eggs were replaced by enriched foods containing vitamin D. After 20 months an online follow-up questionnaire was sent out, to which 123 participants responded with complete data.
Results and discussion: Vitamin D deficiency (total 25(OH)D <50 nmol/L) was found in 29.0 % of premenopausal and 24.4 % of postmenopausal women. Vitamin D insufficiency (total 25(OH)D <75 nmol/L) was found in 76.8 % of premenopausal and 61.7 % of postmenopausal women. In premenopausal women, total 25(OH)D levels were 11.8 % lower and bioavailable 25(OH)D levels were 32.2 % lower than in postmenopausal women. The odds ratio (OR) for vitamin D insufficiency (total 25(OH)D <75 nmol/L) among vitamin D non-supplementers was OR = 6.23; p<0.001. Vitamin D supplementation increased 7-fold compared to pre-pandemic levels and remained at a high level after 20 months. With (bio)fortification it would be possible to cost-effectively increase the average intake of vitamin D from 2.2±1.3 µg/d (no fortification) to 10.5±6.5 µg/d (biofortification of eggs, fortification of milk yoghurt)
Conclusions: A screening questionnaire would not be reliable enough to predict low serum levels of total 25(OH)D. Vitamin D supplementation with medications and supplements has been shown to be an effective, although unlike food fortification, it is only effective at the individual level. The goal of food fortification should be to eradicate severe vitamin D deficiency (25(OH)D <30 nmol/L) and prevent vitamin D deficiency (25(OH)D <50 nmol/L) in the majority of the population. To achieve optimal values (>75 nmol/L), the addition of vitamin D through medication or food supplements would still be necessary from October to April. During the Covid-19 pandemic, the promotion of vitamin D supplementation in the media proved to be very successful, so it would make sense to implement it systematically and continuously.
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