science

Vitamin D deficiency

Vitamin D deficiency is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Vitamin D deficiency rather than just read about it. In short: Vitamin D deficiency or hypovitaminosis D is a vitamin D level that is below normal. It most commonly occurs in people when they have inadequate exposure to sunlight, particularly sunlight with adequate ultraviolet B rays.

Key takeaways

Vitamin D deficiency belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Vitamin D deficiency to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Vitamin D deficiency from memory before moving on to harder problems.

Reference excerpt

Vitamin D deficiency or hypovitaminosis D is a vitamin D level that is below normal. It most commonly occurs in people when they have inadequate exposure to sunlight, particularly sunlight with adequate ultraviolet B rays. Vitamin D deficiency can also be caused by inadequate nutritional intake of vitamin D; disorders that limit vitamin D absorption; and disorders that impair the conversion of vitamin D to active metabolites, including certain liver, kidney, and hereditary disorders. Deficiency impairs bone mineralization, leading to bone-softening diseases, such as rickets in children. It can also worsen osteomalacia and osteoporosis in adults, increasing the risk of bone fractures. Muscle weakness is also a common symptom of vitamin D deficiency, further increasing the risk of falls and bone fractures in adults. Vitamin D can be synthesized in the skin under exposure to UVB from sunlight. Oily fish, such as salmon, herring, and mackerel, are also sources of vitamin D, as are mushrooms. Milk is often fortified with vitamin D; sometimes bread, juices, and other dairy products are fortified with vitamin D. Many multivitamins contain vitamin D in different amounts.

Classifications

Vitamin D deficiency is typically diagnosed by measuring the concentration of the 25-hydroxyvitamin D in the blood, which is the most accurate measure of stores of vitamin D in the body. One nanogram per millilitre (1 ng/mL) is equivalent to 2.5 nanomoles per litre (2.5 nmol/L). The National Institutes of Health cautions that "serum concentrations of 25(OH)D that are associated with vitamin D deficiency have not been definitively identified," but endorses the following guidelines:

Deficient: <12 ng/mL = <30 nmol/L Inadequate: 12–20 ng/mL = 30–50 nmol/L Adequate: ≥20 ng/mL = ≥50 nmol/L Potentially Excessive: >50 ng/mL = >125 nmol/L Some researchers characterize <12 ng/mL (or <30 nmol/L) as severe deficiency, stating that it "dramatically increases the risk of excess mortality, infections, and many other diseases." Vitamin D levels falling within the adequate range prevent clinical manifestations of vitamin D insufficiency as well as vitamin D toxicity. The Endocrine Society previously characterized 20 ng/mL - 29 ng/mL as "insufficiency", but updated its guidelines in 2024.

Signs and symptoms

In most cases, vitamin D deficiency is almost asymptomatic. It may only be detected on blood tests but is the cause of some bone diseases and is associated with other conditions:

Complications Rickets, a childhood disease characterized by impeded growth and deformity of the long bones. The earliest sign of vitamin D deficiency is craniotabes, abnormal softening or thinning of the skull. Osteomalacia, a bone-thinning disorder that occurs exclusively in adults and is characterized by proximal muscle weakness and bone fragility. Women with vitamin D deficiency who have been through multiple pregnancies are at elevated risk of osteomalacia. Osteoporosis, a condition characterized by reduced bone mineral density and increased bone fragility Increased risk of fracture Myopathy: Muscle aches, weakness, and twitching (fasciculations) due to reduced blood calcium (hypocalcemia); impaired muscle glycogen metabolism (abnormal glycogen accumulation), atrophy of type II (fast-twitch/glycolytic) muscle fibres, and diminished calcium uptake by the sarcoplasmic reticulum (needed for muscle contraction). Periodontitis, local inflammatory bone loss that can result in tooth loss. Pre-eclampsia: There has been an association between vitamin D deficiency and women who develop pre-eclampsia in pregnancy. The exact relationship of these conditions is not well understood. Maternal vitamin D deficiency may affect the baby, causing overt bone disease from before birth and impairment of bone quality after birth. Respiratory infections and COVID-19: Vitamin D deficiency may increase the risk of severe acute respiratory infections and COPD. Emerging studies have suggested a link between vitamin D deficiency and COVID-19 symptoms. A review has shown that vitamin D deficiency is not associated with a higher chance of having COVID-19 but is associated with a greater severity of the disease, including 80% increases in the rates of hospitalization and mortality. Schizophrenia: Vitamin D deficiency is associated with the development of schizophrenia. People with schizophrenia generally have lower levels of vitamin D. The environmental risk factors of seasonality of birth, latitude, and migration linked to schizophrenia all implicate vitamin D deficiency, as do other health conditions such as maternal obesity. Vitamin D is essential for the normal development of the nervous system. Maternal vitamin D deficiency can cause prenatal neurodevelopmental defects, which influence neurotransmission, altering brain rhythms and the metabolism of dopamine. Vitamin D receptors, CYP27B1, and CYP24A1 are found in various regions of the brain, showing that vitamin D is a neuroactive, neurosteroid hormone essential for the development of the brain and normal function. Depression and Anxiety: Vitamin D deficiency is associated with increased symptoms of depression and anxiety, and screening is recommended in the prevention and treatment of planning these mood disorders. There is also a possible link between Vitamin D deficiency and the development of OCD.

Risk factors Those most likely to be affected by vitamin D deficiency are people with little exposure to sunlight. Certain climates, dress habits, the avoidance of sun exposure, and the excessive use of sunscreen protection can limit production of vitamin D in the skin.

Age Elderly people have a higher risk of having a vitamin D deficiency due to a combination of several risk factors, including decreased sunlight exposure, decreased intake of vitamin D in the diet, and decreased skin thickness, which leads to further decreased absorption of vitamin D from sunlight.

Fat percentage Since vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol) are fat-soluble, humans and other animals with a skeleton need to store some fat. Without fat, the animal will have a hard time absorbing vitamin D2 and vitamin D3, and the lower the fat percentage, the greater the risk of vitamin deficiency, which is the case in some athletes who strive to get as lean as possible.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Vitamin D deficiency

Start with the simplest possible case. Write down what Vitamin D deficiency claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Vitamin D deficiency before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Vitamin D deficiency ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Vitamin D deficiency

In research: Vitamin D deficiency appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Vitamin D deficiency in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Vitamin D deficiency is common in secondary-school and first-year university syllabi. It links to neighbouring topics Vitamin D, Vitamin deficiencies, so understanding it makes those chapters shorter.
In everyday life: Look for Vitamin D deficiency outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Vitamin D deficiency in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Vitamin D deficiency means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Vitamin D deficiency out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Vitamin D deficiency in simple terms?

Why does Vitamin D deficiency matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Vitamin D deficiency?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Vitamin D deficiency.