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Hypovitaminosis D
*Hypovitaminosis D*
For medical students2 min readUpdated 2026-10-10
Hypovitaminosis D is a pathological condition resulting from vitamin D deficiency or hereditary defects in the proteins involved in its metabolism. The disease is characterized by a drop in calcitriol levels, impaired calcium absorption, and the development of hypocalcemia. The primary clinical manifestation of this deficiency in children is rickets.
EtiologyHereditary forms are caused by genetic defects in metabolic polypeptides.
D-hormonePathogenesis is triggered by a drop in the synthesis of the active metabolite, calcitriol.
MetabolismDecreased intestinal calcium absorption inevitably leads to hypocalcemia.
NosologyThe main manifestation of vitamin D deficiency in childhood is rickets.
Pathogenesis and Etiological Factors
The development of the pathological process may be associated with genetic defects in polypeptide chains responsible for the normal transformation of the vitamin in the body.
The cascade of core pathogenetic links develops in the following sequence:
Onset of vitamin D deficiency.
Drop in the production of its active metabolite — calcitriol (D-hormone).
Decreased intestinal absorption of calcium.
Development of hypocalcemia followed by the activation of compensatory mechanisms.
Role of Vitamin D in Calcium-Phosphorus Metabolism
The active metabolite of vitamin D performs key regulatory functions in the body:
Stimulation of parathyroid hormone (PTH) secretion: Enhances bone tissue resorption, which maintains physiological blood calcium concentrations.
Renal effects: Increases calcium reabsorption and stimulates phosphate excretion, preserving an optimized Ca/P balance.
Extraskeletal action: Through specific calcitriol receptors located in numerous organs, the hormone regulates cell division, growth, and differentiation, and participates in hormonal synthesis.
Clinical Manifestations and Skeletal Deformities in Rickets
Rickets is the primary consequence of hypovitaminosis D. Disruption of calcium-phosphorus metabolism leads to a group of structural skeletal pathologies.
Form of Disorder
Pathogenetic Essence and Clinical Picture
Impaired Mineralization
Weakened mineralization manifests as osteoporosis and an increased frequency of fractures.
Osteomalacia
The process of bone resorption leading to skeletal softening.
Bone Deformities
Formation of "rachitic rosary" (enlargements at the costochondral junctions), curvature of the spine and limbs, and softening of the flat bones of the skull.
Dental and Muscular Disorders
D-hormone deficiency affects not only the skeletal system but also other tissues:
Dental status: There is a marked delay in the eruption of primary teeth, as well as dentin formation defects.
Muscle hypotonia: Reduced muscle tone is associated with impaired innervation, metabolic disorders in muscle fibers, and disturbed assimilation of key micronutrients—Ca, P, and Mg.
Mnemonic
Deficiency pathogenesis chain: Deficiency of D -> Calcitriol ↓ -> Absorption of Ca ↓ -> Hypocalcemia (D-C-A-H).
Frequently asked questions
What are the types of hereditary defects in vitamin D metabolism?
Literature describes the following hereditary defects in vitamin D metabolism:
Recessive defect of renal α1-hydroxylase, leading to developmental delay and rachitic skeletal changes (treated with high doses of vitamin D).
Defect of cellular calcitriol receptors, where clinical features resemble α1-hydroxylase deficiency, but are accompanied by alopecia, epidermal cysts, and muscle weakness.
How do blood biochemical parameters (calcium, phosphorus, alkaline phosphatase) change in established rickets?
The degree of change in blood biochemical parameters depends on the severity of rickets, reflecting the depth of vitamin D deficiency:
Grade I severity: Calcium and phosphorus levels are within normal limits or slightly reduced; alkaline phosphatase (ALP) is elevated.
Grade II severity: Phosphorus is consistently decreased (hypophosphatemia), calcium is at the lower limit of normal or decreased, and ALP continues to rise.
Grade III severity: Loss of compensation, marked drop in both phosphorus and calcium (hypocalcemia), with maximal ALP values observed.
What reduction does vitamin D deficiency lead to at the initial stage of pathogenesis?
The primary key link is a drop in the synthesis of the active metabolite—calcitriol (D-hormone), which subsequently leads to reduced intestinal calcium absorption.
What effect does vitamin D have on renal function?
In the renal tubules, it promotes increased calcium reabsorption and enhances phosphate excretion to maintain the Ca/P ratio.
What explains the development of muscle hypotonia in rickets?
Muscle hypotonia is caused by impaired innervation, disruption of local metabolic processes, and defective assimilation of calcium, magnesium, and phosphorus.
What are "rachitic rosary" beads?
These are characteristic bone deformities in the form of swellings that form at the junction of the bone and cartilage tissues.
Go deeper
Genetic defects of vitamin D metabolic polypeptides
Molecular mechanisms of calcitriol action on cell division and differentiation
Pathophysiology of osteomalacia and osteoporosis in calcium-phosphorus disorders
The role of parathyroid hormone and bone resorption in maintaining calcium homeostasis
Mechanisms of impaired dentin development in hypovitaminosis D