Calcitriol’s role in fetal bone and mineral metabolism: Evidence from human and animal studies
Bibliographic record
Abstract
Fetal mineral and bone metabolism is regulated differently compared to the neonate, child, or adult. A fundamental design difference is that the fetal mineral supply comes from active transport across the placenta rather than the intestines. Calcium, phosphorus, and magnesium also circulate at higher concentrations in the fetal blood as compared to maternal or normal adult values, which facilitates rapid accretion of skeletal mineral content before birth. Given the dependence of postnatal mineral and bone homeostasis on calcitriol, it may be expected that calcitriol and the vitamin D receptor (VDR) would be critically required during fetal development. However, calcitriol circulates at low levels in the fetal circulation, kept suppressed by increased 24-hydroxylated catabolism and low parathyroid hormone (PTH). Calcitriol does not regulate placental mineral transport, while the intestines are a trivial route of mineral delivery in the fetus. Consequently, fetuses lacking vitamin D, calcitriol, or VDRs are born with normal serum mineral concentrations, PTH, and skeletal development/mineralization. After birth, serum calcium falls and phosphorus rises, and these events trigger an increase in PTH and a subsequent rise in calcitriol. The intestines become the main source of mineral supply and it is then that the neonatal may begin to suffer the consequences of disrupted vitamin D physiology. This review discusses key data arising from animal and human studies (clinical trials, case series, epidemiological studies, associational analyses) in order to address our current knowledge on the role of vitamin D, calcitriol, and VDR in regulating fetal mineral and bone homeostasis.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.004 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".