bubble_chart Overview

Vitamin D deficiency is a common chronic nutritional deficiency in infants and young children. It occurs due to insufficient vitamin D, leading to abnormal calcium and phosphorus metabolism in the body, resulting in skeletal development disorders. Severe cases may cause skeletal deformities, known as rickets. When vitamin D deficiency is combined with sluggish parathyroid response, serum calcium levels drop, increasing neuromuscular excitability and leading to convulsions or tetany, referred to as tetany syndrome. This condition affects children's healthy development, weakens their constitution, and increases susceptibility to other diseases, especially respiratory illnesses. Therefore, active prevention and treatment of this condition are crucial tasks in child healthcare.

bubble_chart Etiology

Vitamin D is a fat-soluble vitamin. Endogenous vitamin D₃ (cholecalciferol) and dietary vitamin D₃, vitamin D₂ (ergocalciferol) are storage forms in the body and lack biological activity. They must undergo hydroxylation in the liver and kidneys to become the hormonal forms of vitamin D₂ and vitamin D₃, which are biologically active.

The inactive (storage form) vitamin D₃, after entering the human body, is converted by the hepatic cell Neijing 25-hydroxylase system into 25-hydroxycholecalciferol [25-(OH)D₃] (with weak anti-rickets activity). Subsequently, under the action of the renal proximal tubule cell Neijing 1α-hydroxylase, it is transformed into 1,25-dihydroxycholecalciferol [1,25-(OH)₂D₃] (the active form in the body, exhibiting hormonal characteristics and strong anti-rickets activity). Through the action of 24-hydroxylase, 25-(OH)D₃

is converted into 24,25-dihydroxycholecalciferol [24,25-(OH)₂D₃], and 1,25-(OH)₂D₃ and 24,25-(OH)₂D₃ are transformed into 1,24,25-trihydroxycholecalciferol [1,24,25-(OH)3D₃]. The synthesis of 25-(OH)D₃, 1,25-(OH)₂D₃, 24,25-(OH)₂D₃, and 1,24,25-(OH)3D₃ is regulated by feedback mechanisms. Excessive synthesis can inhibit their respective enzyme systems, slowing down the synthesis process, thereby maintaining dynamic balance in the body. The production of 1,25-(OH)₂D₃ in the kidneys is regulated by serum calcium and phosphorus concentrations, parathyroid hormone, calcitonin, etc. Parathyroid hormone promotes the conversion of 25-(OH)D₃ into 1,25-(OH)₂D₃, while high blood phosphorus and calcitonin inhibit this conversion. Low blood calcium stimulates parathyroid secretion and inhibits calcitonin secretion, whereas high blood calcium has the opposite effect, indirectly influencing the production of 1,25-(OH)₂D₃. The metabolism of vitamin D₂ is the same as that of vitamin D₃.

1. The primary physiological functions of 1,25-(OH)₂D₃ include:
   1. Promoting intestinal absorption of calcium and phosphorus.
   2. Enhancing renal tubular reabsorption of calcium and phosphorus.
   3. On one hand, it can promote osteoclast activity and enhance the effect of parathyroid hormone in mobilizing bone calcium, facilitating the decalcification of old bone, dissolving bone salts in old bone, and transporting calcium and phosphorus into the blood to increase the concentration of extracellular calcium and phosphorus. On the other hand, it promotes the function of osteoblasts, causing calcium and phosphorus in the blood to deposit at bone formation sites, thereby forming new bone.
2. Factors of Vitamin D Deficiency
   1. Insufficient Sunlight Exposure: Ultraviolet rays from sunlight can convert 7-dehydrocholesterol in the skin into vitamin D₃ (endogenous cholecalciferol). The daily requirement of vitamin D is primarily obtained through sunlight exposure, with only a small portion supplied by food. Infants and young children living in cold regions may not frequently engage in outdoor activities during winter. Additionally, excessive air pollution, prolonged rainy or foggy seasons, as well as clothing and glass, can reduce the duration and intensity of sunlight exposure, thereby decreasing endogenous vitamin D production. In northern China, winters are longer, and sunlight strikes the ground at an oblique angle, resulting in shorter daylight hours. Consequently, this condition is more prevalent in the north than in the south and occurs more often in winter than in summer.
   2. Inadequate Intake: Human milk, cow’s milk, lance asiabell root, and most common foods contain only small amounts of vitamin D. If infants are not regularly exposed to sunlight and are not supplemented with vitamin D-rich foods, they are more susceptible to this condition. Formula-fed infants are at higher risk than breastfed ones. Therefore, promoting breastfeeding holds certain significance in preventing this condition.
   3. Rapid Growth and Development: During infancy, the rapid growth and development increase the demand for vitamin D and calcium. This is especially true for premature and multiple-birth infants, whose stores of calcium, phosphorus, and vitamin D are insufficient, leading to even greater requirements. If an adequate supply of vitamin D is lacking, this condition is more likely to occur.
   4. Disease Impact: Chronic gastrointestinal and hepatobiliary diseases can impair the absorption and utilization of vitamin D. Chronic respiratory diseases often accompany chronic acidosis, while liver and kidney disorders may hinder the hydroxylation of vitamin D.
   Thus, these factors are closely related to the occurrence of this condition.

Both rickets and convulsive disorders stem from vitamin D deficiency, but their clinical manifestations differ, primarily due to the compensatory function of the parathyroid glands.

bubble_chart Clinical Manifestations

The earliest symptoms include loss of appetite, even anorexia, dysphoria, crying, and lethargy, often accompanied by low-grade fever, and may include nausea, vomiting, constipation, drowsiness, and apathy. Gradually, symptoms such as polydipsia, excessive drinking, and polyuria appear. Older children may complain of headaches, with elevated or decreased blood pressure, and systolic murmurs may be heard in the heart. Severe cases can lead to mental depression, hypotonia, ataxia, and renal failure. Long-term chronic poisoning can result in organ calcification, affecting physical and intellectual development.

bubble_chart Auxiliary Examination

Increased blood calcium, normal, elevated, or decreased blood phosphorus, decreased alkaline phosphatase levels, azotemia; decreased urine specific gravity, presence of protein, red blood cells, and casts in urine; ST segment elevation may be observed on the electrocardiogram.

[X-ray examination] Features include increased density and widening of the provisional calcification zone at the metaphysis of long bones, thickened bone cortex, increased and blurred density of trabeculae, thickened margins of flat and round bones forming dense ring-like shadows; severe cases may show calcifications in the brain, heart blood vessels, trachea, kidneys, and soft tissues of the limbs.

bubble_chart Diagnosis

The diagnosis can be made based on clinical symptoms and signs, X-ray skeletal changes, and blood generation and transformation test results, combined with factors such as age, season, region, history of premature labor, multiparity, insufficient sunlight exposure, feeding without vitamin D supplementation, and chronic diseases (e.g., gastrointestinal, hepatobiliary, or respiratory system disorders). Additionally, it is necessary to determine whether the condition is in the active phase and its grade (Grade I), as this is relevant to medication dosage and whether treatment is required. Vitamin D therapy is only meaningful during the active phase.

bubble_chart Treatment Measures

1. Vitamin D Therapy: For active rickets, categorized as grades I, II, and III, administer oral vitamin D concentrate daily at doses of 5,000–10,000 IU, 10,000–20,000 IU, and 20,000–40,000 IU, respectively, for one month, then switch to preventive doses. Alternatively, a shock therapy may be used: for grades I, II, and III, the initial doses are 300,000 IU and 600,000 IU, to be taken within 1–2 days, or intramuscular injection of vitamin D₃300,000–600,000 IU, administered once every 1–2 weeks for a total of 1–3 injections, along with calcium supplements. After one month, assess efficacy through X-ray and generation and transformation examinations to determine subsequent dosages. If improvement is observed, switch to general therapeutic or preventive doses.
2. Nursing Care: Encourage outdoor activities to expose the patient to sunlight and fresh air. Ultraviolet lamp irradiation may be used if necessary. Avoid prolonged sitting, standing, or walking, and refrain from forcing the child to learn standing or walking prematurely.
3. Orthopedic Treatment: Most deformities in infantile rickets correct spontaneously during treatment. For severe deformities, consider corrective surgery after the active phase has ended.

bubble_chart Prevention

The incidence of this disease remains relatively high in China, posing significant health risks to infants and young children. It is essential to adhere to the principle of prevention first, emphasizing comprehensive group preventive measures, and to widely promote health education. Special attention should be paid to disseminating knowledge on maternal health during pregnancy and lactation, as well as scientific childcare practices. Specific measures are as follows.

1. Pregnant and lactating mothers should ensure adequate exposure to sunlight and consume foods rich in vitamin D. If necessary, they may take vitamin D supplements at 400–800 IU/day along with an appropriate amount of calcium.
2. Infants and young children should engage in more outdoor activities and get sufficient sunlight to increase endogenous vitamin D production. Infants as young as one month old can be taken outdoors in summer, and those older than three months can also be exposed to sunlight in winter. Exposing 1 cm² of skin to sunlight for one hour yields approximately 6 IU of vitamin D. Regular sunbathing during summer and autumn can store enough vitamin D in the body to last for several months.
3. Practice proper feeding, prioritizing breastfeeding, and promptly introduce foods rich in vitamin D.
4. Actively prevent and treat common and frequent illnesses in infants and young children, such as respiratory and digestive system diseases.
5. Vitamin D supplementation: Generally, infants should start receiving 400 IU/day of vitamin D from 2–3 months of age. For premature births, twins or multiples, babies born in late summer or autumn/winter, formula-fed infants, or those with rapid growth, supplementation should begin at 2–3 weeks of age, with dosage adjusted as needed.

Vitamin D deficiency rickets

Vitamin D deficiency rickets remains one of the prevalent diseases among children in China at this stage. The national average prevalence is 40.7%, with regional averages of 49.39% in the north, 33.11% in the central region, and 24.64% in the south. The highest prevalence occurs in infants under one year old, ranging from 40–80% in the north and 30–60% in the south. The prevalence of congenital rickets is 5–30%. In the north, incidence peaks in winter and spring, often in the active phase, while seasonal differences are less pronounced in the south.

Although rickets rarely directly endangers life, it severely impacts the normal growth and development of children. Due to its slow onset, it is easily overlooked. Once obvious symptoms appear, the body's resistance declines, increasing susceptibility to serious complications such as pneumonia and diarrhea.

bubble_chart Differentiation

1. Cretinism: Growth and development are delayed, and the body is significantly shorter, similar to rickets. However, patients with this condition exhibit poor intelligence, thick and large tongue, thick lips, coarse voice, low body temperature, and severe constipation. Serum calcium and phosphorus levels are normal. X-rays show delayed bone age compared to normal peers, but calcification is normal.
2. Chondrodystrophy: This disease involves cartilage development disorders, and the body shape closely resembles rickets. Its characteristics include a square and large head, prominent forehead, lumbar lordosis, protruding abdomen, protruding buttocks, short and thick limbs, hands not reaching the hips, flat fingers, and trident hand. Serum calcium and phosphorus levels are normal. X-rays reveal enlarged long bone ends, narrow epiphyseal plates, and normal provisional calcification zones.
3. Congenital osteogenesis imperfecta: Deafness, blue sclerae, and fragile bones prone to fractures are the three main features. Frequent fractures often lead to limb deformities. X-rays show thin bone cortex, fractures, and deformities.
4. Down syndrome: Although physical and motor development are delayed, and muscle hypotonia resembles rickets, the typical facial features—flat nasal bridge, wide-set eyes, upward-slanting palpebral fissures, and protruding tongue—combined with intellectual disability and simian crease make it easy to distinguish from rickets. Chromosomal testing can confirm the diagnosis.
5. Congenital hypotonia: Lax muscles and ligaments, hyperextensible joints, normal blood generation and transformation, and no abnormalities in X-ray bone structure.
6. Renal rickets: Chronic renal dysfunction caused by congenital renal hypoplasia or acquired kidney disease leads to significant osteomalacia, termed renal osteodystrophy. Serum calcium is reduced, and serum phosphorus is elevated. X-rays often show generalized bone decalcification, with typical rickets-like changes at the long bone epiphyses. Severe cases may exhibit fibrous cystic changes in the bone shafts and pelvis. Treatment focuses on improving renal function and administering 1,25-(OH)₂D₃ or high-dose vitamin D₃.
7. Distal renal tubular acidosis: Clinical manifestations closely resemble rickets, including severe generalized bone decalcification, skeletal deformities, and fractures. Epiphyseal changes are similar to rickets. This condition is characterized by alkaline urine, metabolic acidosis, hyperchloremia, hypophosphatemia, and hypokalemia. Due to hypokalemia, episodes of limb weakness and flaccid paralysis are common, and general fatigue is persistent. Prognosis is poor.