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Calciferol (Vitamin D): Functions, Requirements and Deficiency

Calciferol is the chemical name for vitamin D, a fat-soluble vitamin and prohormone that the body can produce through sunlight exposure and that is essential for bone health, immune function, and muscle strength.

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Things worth knowing about "Calciferol"

Calciferol is the chemical name for vitamin D, a fat-soluble vitamin and prohormone that the body can produce through sunlight exposure and that is essential for bone health, immune function, and muscle strength.

What is Calciferol?

Calciferol is the collective term for the various forms of vitamin D, a fat-soluble vitamin and prohormone. The two most biologically relevant forms are vitamin D2 (ergocalciferol), found primarily in plants and fungi, and vitamin D3 (cholecalciferol), which is synthesized in human skin upon exposure to UV-B radiation from sunlight. Calciferol plays a central role in calcium and phosphate metabolism and is indispensable for healthy bone development and numerous other bodily functions.

Biological Functions

After absorption or synthesis, calciferol is converted in the liver to 25-hydroxyvitamin D (calcidiol) and subsequently in the kidneys to the biologically active form 1,25-dihydroxyvitamin D (calcitriol). Calcitriol acts like a hormone by binding to specific vitamin D receptors found in many body tissues. Key functions include:

Bone health: Regulation of calcium and phosphate absorption in the intestine and mineralization of bones and teeth.
Immune system: Support of innate and adaptive immune responses and regulation of inflammatory processes.
Muscle function: Promotion of muscle performance and reduction of fall risk in older adults.
Cell growth: Involvement in regulating cell division and differentiation.
Cardiovascular system: Potential protective effects on blood pressure and cardiac function.

Dietary Sources

The human body can synthesize vitamin D3 through sun exposure on the skin. In addition, relevant dietary sources include:

Fatty fish such as salmon, herring, and mackerel
Cod liver oil
Egg yolk
Liver
UV-irradiated mushrooms (vitamin D2)
Vitamin D-fortified foods such as milk, margarine, and breakfast cereals

Recommended Intake

Recommendations for daily vitamin D intake vary by organization and age group. The World Health Organization (WHO) and many national health bodies recommend a daily intake of 600 to 800 IU (15 to 20 µg) for most adults, with higher amounts suggested for older individuals. Infants are generally given vitamin D supplements to prevent rickets, as breast milk alone does not provide sufficient amounts.

Deficiency Symptoms

A calciferol deficiency can have wide-ranging health consequences:

Rickets in children: softening and deformity of the bones
Osteomalacia in adults: bone softening causing pain and muscle weakness
Osteoporosis: increased risk of bone loss and fractures
Muscle weakness and muscle pain
Increased susceptibility to infections
Fatigue and depressive mood

Groups at risk of calciferol deficiency include older adults, individuals with darker skin tones, people with limited sun exposure, pregnant and breastfeeding women, and patients with malabsorption syndromes.

Toxicity and Overdose

As calciferol is a fat-soluble vitamin, it can accumulate in the body. Toxicity typically occurs only through high-dose supplementation and not from sunlight or normal dietary intake. Symptoms of calciferol poisoning (hypervitaminosis D) include:

Nausea, vomiting, and loss of appetite
Elevated blood calcium levels (hypercalcemia)
Kidney damage due to calcium deposits
Cardiac arrhythmias

The tolerable upper intake level set by the European Food Safety Authority (EFSA) for adults is 100 µg (4,000 IU) per day.

Interactions

Calciferol may interact with various medications and nutrients:

Calcium: Calciferol enhances calcium absorption; combined high-dose intake may increase the risk of hypercalcemia.
Thiazide diuretics: Combination may lead to elevated calcium levels in the blood.
Corticosteroids: May impair vitamin D metabolism and reduce its effectiveness.
Cholestyramine and orlistat: Inhibit fat absorption and therefore also reduce the absorption of calciferol.
Vitamin K2: Acts synergistically with calciferol in bone mineralization.

References

Holick MF: Vitamin D Deficiency. New England Journal of Medicine 2007; 357:266-281. doi:10.1056/NEJMra070553
European Food Safety Authority (EFSA): Dietary reference values for vitamin D. EFSA Journal 2016; 14(10):4547. doi:10.2903/j.efsa.2016.4547
World Health Organization (WHO): Vitamin D supplementation in infants, children and adolescents. WHO Guidelines, 2022. www.who.int

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