Overview
The document describes Vitamin D as a fat-soluble, secosteroid hormone essential for calcium and phosphorus metabolism. It is also known as the anti-rachitic factor and the sunshine vitamin. Its active form, 1,25-dihydroxy cholecalciferol (Calcitriol), functions like a steroid hormone and plays a central role in bone growth, immune modulation, and mineral balance.
Vitamin D exists in two primary forms:
- Vitamin D₂ (Ergocalciferol) – derived from plant sources
- Vitamin D₃ (Cholecalciferol) – derived from animal sources or synthesized in the skin through UVB exposure
The document shows that Vitamin D synthesis begins in the skin, where UV light converts cholesterol to Vitamin D₃, followed by activation in the liver and kidneys. Regulation of synthesis depends on factors such as PTH, estrogen, calcium levels, phosphate levels, and FGF-23. Vitamin D works on the bone, intestine, and kidney to maintain calcium homeostasis along with PTH and calcitonin.
The document also outlines dietary sources such as fatty fish, cod liver oil, egg yolk, fortified foods, mushrooms exposed to UV light, and sunlight, which remains the most significant natural source.
Symptoms
Symptoms of Vitamin D imbalance arise from either deficiency or toxicity, both of which are explained within the document.
Symptoms of Deficiency
Vitamin D deficiency leads to impaired bone mineralization and affects musculoskeletal health. Document-based symptoms include:
- Bone pain and soft, weak bones
- Poor bone mineralization leading to rickets in children
- Osteomalacia in adults, resulting in bone demineralization
- Muscle weakness
- Increased fracture risk
- Manifestations related to renal osteodystrophy
- Symptoms arising from hypoparathyroidism due to a calcium imbalance
Symptoms of Toxicity
When Vitamin D levels exceed the upper range, typically due to excessive supplementation, symptoms may include:
- Loss of appetite
- Nausea
- Thirst
- Stupor
- Calcium deposition in tissues
- Calcinosis (soft tissue calcification)
These symptoms result from hypercalcemia, which arises when Vitamin D intake is chronically excessive.
Causes
The document provides a detailed list of contributing factors behind Vitamin D deficiency, reflecting dietary, environmental, metabolic, and physiological triggers.
Major causes include:
- Inadequate dietary intake of Vitamin D-rich foods
- Limited sunlight exposure
- Dark skin pigmentation, reducing UV absorption
- Malabsorption syndromes such as celiac disease and Crohn’s disease
- Liver disease affects Vitamin D conversion
- Kidney disease reduces its final activation
- Medications like anticonvulsants and steroids
- Obesity, which sequesters Vitamin D in fat stores
- Breastfeeding without supplementation
- Cultural clothing practices limit sun exposure
- Pollution, which restricts UVB penetration
- Natural aging, which decreases the skin’s ability to synthesize Vitamin D
- Cow’s milk allergy or dietary restriction
These causes collectively impair Vitamin D availability, metabolism, or utilization.
Risk Factors
Risk factors align with the causes but highlight populations more vulnerable to Vitamin D imbalance:
- Infants, children, and older adults due to higher nutritional needs or reduced skin synthesis
- Individuals with limited outdoor activity or those who cover most of their skin
- People living in polluted regions or areas with low sunlight
- Those with gastrointestinal disorders, chronic liver disease, or kidney disease
- People taking specific medications that interfere with Vitamin D metabolism
- Individuals with autoimmune disorders, as low Vitamin D is associated with reduced immune tolerance
- Patients with cardiovascular disease, since low Vitamin D status correlates with hypertension and atherosclerosis
The document also highlights that high Vitamin D levels (hypervitaminosis D) pose risks due to hypercalcemia and toxicity.
Prevention
Prevention in the document focuses on maintaining healthy Vitamin D levels through balanced exposure, diet, monitoring, and proper testing.
Key preventive strategies include:
- Ensuring adequate sunlight exposure to stimulate natural Vitamin D synthesis
- Consuming dietary sources such as fatty fish, eggs, fortified milk, fortified cereals, fortified juices, and UV-exposed mushrooms
- Appropriate supplementation based on the Recommended Daily Allowances (RDA), which vary among infants, adults, pregnant women, and lactating mothers
- Regular screening using serum Vitamin D levels, especially in at-risk groups
- Proper sample collection, including drawing 3 mL of blood in a plain tube, early serum separation, and refrigeration if delayed
- Using validated testing methods, such as immunoassays, HPLC, LC-MS/MS, and competitive binding assays
- Monitoring supplementation carefully to avoid toxicity
- Addressing underlying conditions like liver, kidney, or malabsorption disorders
Together, these preventive steps support optimal Vitamin D status, helping maintain strong bones, balanced calcium metabolism, and healthy immune function.
