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The majority of either 25OHD or 1,25(OH)<jats:sub>2<\/jats:sub>D is bound to vitamin D-binding protein (DBP), a smaller fraction is bound to albumin and only very small amounts of 25OHD or 1,25(OH)<jats:sub>2<\/jats:sub>D are free. Albumin-bound 25OHD or 1,25(OH)<jats:sub>2<\/jats:sub>D is relatively easily available after dissociation from albumin. Thus, the sum of free and albumin-bound forms is called bioavailable 25OHD and bioavailable 1,25(OH)<jats:sub>2<\/jats:sub>D. Total 25OHD and 1,25(OH)<jats:sub>2<\/jats:sub>D are defined as the sum of free, albumin-bound and DBP-bound 25OHD and 1,25(OH)<jats:sub>2<\/jats:sub>D, respectively. This cross-sectional study in 427 pregnant women compared the correlation of the six vitamin D compounds with biomarkers of bone health, lipid metabolism, kidney function, endocrine parameters, and group B water-soluble vitamins. Among the 25OHD metabolites analysed, total 1,25(OH)<jats:sub>2<\/jats:sub>D showed clearly the best correlation with calcium, bone-specific alkaline phosphatase, adiponectin, LDL, HDL, urea, thyroxine, and group B water-soluble vitamins. When comparing the three 25OHD metabolites, both free 25OHD and bioavailable 25OHD showed overall good correlations with calcium, bone-specific alkaline phosphatase, adiponectin, LDL, HDL, urea, thyroxine, triiodothyronine, and group B water-soluble vitamins, The correlations of 1,25(OH)<jats:sub>2<\/jats:sub>D and 25OHD metabolites went always in opposite directions. Only PTH correlates always inversely with all six vitamin D compounds. In conclusion, free 25(OH)D and bioavailable 25(OH)D are more precise determinants of the vitamin D status than total 25(OH)D in normal pregnancy, whereas total 1,25(OH)<jats:sub>2<\/jats:sub>D is superior to free and bioavailable 1,25(OH)<jats:sub>2<\/jats:sub>D. Except for PTH, correlations of 25(OH)D and 1,25(OH)<jats:sub>2<\/jats:sub>D metabolites with typical clinical chemistry readouts go in opposite directions.<\/jats:p>","DOI":"10.1038\/s41598-021-81452-9","type":"journal-article","created":{"date-parts":[[2021,1,21]],"date-time":"2021-01-21T11:03:39Z","timestamp":1611227019000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":24,"title":["Opposite correlation of 25-hydroxy-vitamin D- and 1,25-dihydroxy-vitamin D-metabolites with gestational age, bone- and lipid-biomarkers in pregnant women"],"prefix":"10.1038","volume":"11","author":[{"given":"Oleg","family":"Tsuprykov","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Saban","family":"Elitok","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Claudia","family":"Buse","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Chang","family":"Chu","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Bernhard Karl","family":"Kr\u00e4mer","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Berthold","family":"Hocher","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2021,1,21]]},"reference":[{"key":"81452_CR1","doi-asserted-by":"publisher","first-page":"105","DOI":"10.1016\/j.jsbmb.2017.01.007","volume":"173","author":"D Bikle","year":"2017","unstructured":"Bikle, D., Bouillon, R., Thadhani, R. & Schoenmakers, I. 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