The nutrient composition of 15 commercially available microalgae powders of Arthrospira platensis, Chlorella pyrenoidosa and vulgaris, Dunaliella salina, Haematococcus pluvialis, Tetraselmis chuii, and Aphanizomenon flos-aquae was analyzed. The Dunaliella salina powders were characterized by a high content of carbohydrates, saturated fatty acids (SFAs), omega-6-polyunsaturated fatty acids (n6-PUFAs), heavy metals, and α-tocopherol, whereas the protein amounts, essential amino acids (EAAs), omega-3-PUFAs (n3-PUFAs), vitamins, and minerals were low. In the powder of Haematococcus pluvialis, ten times higher amounts of carotenoids compared to all other analyzed powders were determined, yet it was low in vitamins D and E, protein, and EAAs, and the n6/n3-PUFAs ratio was comparably high. Vitamin B₁₂, quantified as cobalamin, was below 0.02 mg/100 g dry weight (d.w.) in all studied powders. Based on our analysis, microalgae such as Aphanizomenon and Chlorella may contribute to an adequate intake of critical nutrients such as protein with a high content of EAAs, dietary fibers, n3-PUFAs, Ca, Fe, Mg, and Zn, as well as vitamin D and E. Yet, the nutritional value of Aphanizomenon flos-aquae was slightly decreased by high contents of SFAs. The present data show that microalgae are rich in valuable nutrients, but the macro- and micronutrient profiles differ strongly between and within species.

Circulating 25-hydroxyvitamin D (25(OH)D) is regarded as the most reliable biomarker of vitamin D status. However, limited data exist concerning the suitability of 25(OH)D as an indicator of body vitamin D stores and the ability of adipose tissue to mobilize vitamin D. In the first study, in which male mice received different vitamin D₃ doses for three weeks, we found strong linear response relationships between vitamin D₃ intake and levels of vitamin D₃ in the plasma (p < 0.001), liver (p < 0.001) and adipose tissues (p < 0.001), and strong positive correlations between plasma and tissue stores of vitamin D₃ (p < 0.001). Plasma levels of 25(OH)D₃ and 24,25-dihydroxyvitamin D₃ (24,25(OH)₂D₃) showed weak or no correlations with tissue vitamin D₃ stores. Data from a second study demonstrate a strong and rapid response of plasma 25(OH)D₃ in vitamin D₃-treated mice with a low vitamin D status. Additionally, mice fed a vitamin D-free diet showed a strong and rapid decline in vitamin D₃ in the liver, whereas the decline in different adipose tissues was distinctly lower than that in the liver. To conclude, tissue stores of vitamin D₃ were best reflected by plasma vitamin D₃. In contrast to the liver, adipose tissues responded less sensitively to an absence of vitamin D intake.

Purpose: This study investigated whether UVB-exposed wheat germ oil (WGO) is capable to improving the vitamin D status in healthy volunteers. Methods: A randomized controlled human-intervention trial in parallel design was conducted in Jena (Germany) between February and April. Ultimately, 46 healthy males and females with low mean 25-hydroxyvitamin D (25(OH)D) levels (34.9 ± 10.6 nmol/L) were randomized into three groups receiving either no WGO oil (control, n = 14), 10 g non-exposed WGO per day (– UVB WGO, n = 16) or 10 g WGO, which was exposed for 10 min to ultraviolet B-light (UVB, intensity 500–630 µW/cm²) and provided 23.7 µg vitamin D (22.9 µg vitamin D₂ and 0.89 µg vitamin D₃) (+ UVB WGO, n = 16) for 6 weeks. Blood was obtained at baseline, after 3 and 6 weeks and analyzed for serum vitamin D-metabolite concentrations via LC–MS/MS. Results: Participants who received the UVB-exposed WGO were characterized by an increase of circulating 25(OH)D₂ after 3 and 6 weeks of intervention. However, the 25(OH)D₃ concentrations decreased in the + UVB WGO group, while they increased in the control groups. Finally, the total 25(OH)D concentration (25(OH)D₂ + 25(OH)D₃) in the + UVB WGO group was lower than that of the non-WGO receiving control group after 6 weeks of treatment. In contrast, circulating vitamin D (vitamin D₂ + vitamin D₃) was higher in the + UVB WGO group than in the control group receiving no WGO. Conclusion: UVB-exposed WGO containing 23.7 µg vitamin D can increase 25(OH)D₂ levels but do no improve total serum levels of 25(OH)D of vitamin D-insufficient subjects. Trial registration: ClinicalTrials.gov: NCT03499327 (registered, April 13, 2018).