Vitamin D Deficiency: Symptoms, Causes and Treatment

Vitamin D deficiency means the body does not have enough vitamin D to support healthy bones, muscles and calcium balance. Mild deficiency may cause no obvious symptoms. More substantial or prolonged deficiency can contribute to muscle weakness, widespread aches, bone pain and osteomalacia in adults. In children, severe deficiency can cause rickets.

Vitamin D is unusual because the body can make it when skin is exposed to suitable sunlight. In the UK, sunlight is generally not strong enough for reliable vitamin D production during autumn and winter, while diet alone often provides only a limited amount.

A low vitamin D result is common, but it should be interpreted carefully. Tiredness and general aches have many possible causes, and vitamin D testing is not routinely recommended for every person without symptoms or risk factors. When deficiency is confirmed, treatment usually involves vitamin D3 supplements followed by a lower maintenance dose where continued risk remains.

What is vitamin D and why does the body need it?

Vitamin D helps the body absorb calcium and phosphate from the digestive system. These minerals are needed to build and maintain strong bones and teeth.

Vitamin D also contributes to:

• normal muscle function;
• healthy bone mineralisation;
• calcium balance in the blood;
• normal function of parts of the immune system;
• growth and skeletal development in children.

When vitamin D levels remain too low, the body absorbs less calcium from food. It may respond by increasing parathyroid hormone, which helps maintain blood calcium partly by drawing mineral from the skeleton.

Over time, bones can become poorly mineralised and softer than normal. In adults this is called osteomalacia. In growing children, the equivalent condition is called rickets.

Vitamin D2 and vitamin D3

Vitamin D supplements usually contain one of two forms:

• vitamin D3, also called colecalciferol;
• vitamin D2, also called ergocalciferol.

Vitamin D3 is commonly used for prevention and treatment in the UK. Most vitamin D3 is traditionally derived from lanolin, although vegan vitamin D3 made from lichen is also available.

Vitamin D2 is generally suitable for vegans because it is usually produced from fungi or yeast. Product ingredients should still be checked carefully.

How is vitamin D measured?

Vitamin D status is assessed using a blood test called 25-hydroxyvitamin D, often written as 25(OH)D.

This is the main circulating form and provides the best routine indication of vitamin D stores. The active hormone form is not usually measured when investigating ordinary nutritional deficiency because it may remain normal or even rise despite low stores.

What are the symptoms of vitamin D deficiency?

Many people with a low vitamin D result have no clear symptoms. When symptoms are present, they are often vague and develop gradually.

Possible symptoms include:

• muscle weakness;
• difficulty climbing stairs or rising from a chair;
• aching muscles;
• bone pain or tenderness;
• pain in the lower back, pelvis, hips, ribs or legs;
• fatigue or reduced stamina;
• frequent falls, particularly in older adults;
• a change in walking pattern;
• fractures occurring after relatively minor injury.

These symptoms are not specific to vitamin D deficiency. Similar complaints can occur with:

• iron or vitamin B12 deficiency;
• thyroid disease;
• arthritis;
• fibromyalgia;
• muscle conditions;
• poor sleep;
• depression;
• medication side effects;
• physical deconditioning.

A low result may contribute to symptoms without explaining every symptom a person has.

What does vitamin D-related muscle weakness feel like?

Weakness linked to osteomalacia tends to affect the muscles around the hips and shoulders. A person may find it difficult to:

• rise from a low chair without using their arms;
• climb stairs;
• lift objects overhead;
• walk for their usual distance;
• recover balance after stumbling.

This is different from feeling generally tired, although the two can occur together.

What does osteomalacia pain feel like?

Osteomalacia can cause a dull, persistent ache in several areas rather than pain in one precise joint. The ribs, lower back, pelvis, hips and legs may feel tender when pressure is applied.

Severe localised pain should still be assessed for a fracture, arthritis or another cause.

Can vitamin D deficiency cause tiredness?

Some people with deficiency report fatigue, but tiredness alone is not enough to diagnose it. Anaemia, vitamin B12 deficiency, thyroid disease, sleep disorders, infection and mental health conditions may produce very similar symptoms.

Our guide to vitamin B12 deficiency symptoms, causes and treatment explains another common nutritional cause of fatigue and neurological symptoms.

What causes vitamin D deficiency?

Deficiency usually develops because the skin makes too little vitamin D, dietary intake is low, absorption is impaired or the body processes vitamin D abnormally.

Limited sunlight exposure

Sunlight is the main natural source for most people in the UK. Risk increases when someone:

• spends little time outdoors;
• is housebound;
• lives in a care home;
• works mainly indoors;
• usually covers most of their skin outside;
• avoids sunlight because of photosensitivity or medical treatment;
• uses very high sun protection at all times on all exposed skin.

Sunscreen remains important for reducing skin damage and skin-cancer risk. Vitamin D advice should not be interpreted as a recommendation to burn or spend prolonged periods in strong sunlight.

Season and latitude

From roughly October to early March, sunlight in the UK generally does not contain enough ultraviolet B radiation for reliable vitamin D production.

The body relies more heavily during these months on stores built during spring and summer, food and supplements.

Darker skin

Melanin reduces the amount of ultraviolet B radiation reaching the deeper layers of skin where vitamin D is produced.

People with dark skin, including many people of African, African-Caribbean or South Asian heritage, may therefore produce less vitamin D from the same amount of sunlight and are advised to consider supplementation throughout the year in the UK.

This is a physiological effect of skin pigmentation, not a sign that darker skin is unhealthy.

Low dietary intake

Only a limited number of foods naturally contain substantial vitamin D. Low intake is more likely in people who:

• eat little or no oily fish;
• avoid eggs and animal products;
• do not use fortified foods;
• follow a restricted diet;
• have poor appetite;
• experience food insecurity.

Vitamin D can be difficult to obtain from food alone, including for people eating an otherwise balanced diet.

Malabsorption

Vitamin D is fat soluble and needs to be absorbed through the digestive system. Absorption may be reduced by:

• coeliac disease;
• Crohn’s disease;
• some forms of pancreatic disease;
• cholestatic liver disease;
• short bowel syndrome;
• some weight-loss operations;
• other disorders that reduce fat absorption.

People with malabsorption may need higher or specialist doses and monitoring rather than ordinary over-the-counter supplementation.

Obesity

Vitamin D can become distributed into body fat, leaving less available in the circulation. People living with obesity may therefore have lower measured levels and sometimes require an adjusted treatment plan.

This does not mean that every person with a higher body weight is deficient or that weight alone explains a low result.

Liver and kidney disease

The liver and kidneys convert vitamin D into forms the body can use. Significant disease affecting either organ can interfere with this process.

People with chronic kidney disease may require specialist forms of vitamin D rather than ordinary colecalciferol alone.

Medicines

Some medicines can increase vitamin D breakdown or affect bone health, including certain:

• anti-seizure medicines;
• antiretroviral treatments;
• antifungal medicines;
• rifampicin;
• long-term corticosteroids.

Do not stop a prescribed medicine because of a low vitamin D result. The prescribing clinician can review the risks, monitoring and replacement needed.

Who is most at risk?

Anyone can develop vitamin D deficiency, but the likelihood is higher in people who:

• have dark skin;
• rarely spend time outdoors;
• are housebound, frail or living in residential care;
• cover most of their skin when outside;
• are pregnant or breastfeeding and have another risk factor;
• follow a restrictive diet with few fortified foods;
• have coeliac disease, Crohn’s disease or another malabsorption condition;
• have undergone bariatric surgery;
• have chronic liver or kidney disease;
• take medicines that affect vitamin D metabolism;
• have obesity;
• have osteoporosis, osteomalacia or repeated fragility fractures.

Older adults

Older skin produces vitamin D less efficiently. Older people may also spend less time outdoors, eat less and have chronic conditions or medicines affecting bone health.

Muscle weakness and poor balance can increase the risk of falls, creating a harmful combination when bones are already fragile.

Babies and children

Vitamin D is essential for a growing skeleton. Severe deficiency can prevent bones from mineralising normally and lead to rickets.

Possible signs in children include:

• delayed growth;
• bone pain or tenderness;
• delayed walking;
• muscle weakness;
• bowed legs or other skeletal changes;
• delayed tooth development;
• seizures caused by low calcium in severe cases.

Babies under 1 year should usually receive 8.5 to 10 micrograms of vitamin D daily unless they drink at least 500 ml of infant formula each day, because formula is already fortified.

Children aged 1 to 4 years are generally advised to receive 10 micrograms daily throughout the year.

Pregnancy and breastfeeding

Vitamin D supports the pregnant person’s bone and muscle health and contributes to fetal skeletal development.

Pregnant and breastfeeding adults are included in the UK recommendation to consider 10 micrograms daily during autumn and winter, and throughout the year when they have little sunlight exposure or dark skin.

Some people require a different dose because of confirmed deficiency, obesity, malabsorption or another medical factor. This should be discussed with a midwife, GP or specialist.

How is vitamin D deficiency diagnosed?

The blood test used is serum 25-hydroxyvitamin D, or 25(OH)D.

Testing is generally considered when a person has:

• symptoms suggesting osteomalacia;
• unexplained muscle weakness;
• bone pain or tenderness;
• fragility fractures;
• osteoporosis where the result may affect treatment;
• abnormal calcium, phosphate or alkaline phosphatase results;
• a condition causing malabsorption;
• another strong clinical reason to know the level.

NICE does not advise routine testing of every healthy person without symptoms. Someone at risk but otherwise well may simply be advised to take the standard prevention dose.

What do vitamin D results mean?

Exact interpretation depends on the laboratory and clinical context. NICE Clinical Knowledge Summaries generally describes:

• below 25 nmol/L: deficient;
• 25 to 50 nmol/L: may be inadequate for some people;
• above 50 nmol/L: sufficient for most people.

These categories are not absolute. A result of 48 nmol/L does not suddenly become dangerous while 51 nmol/L guarantees perfect bone health.

The clinician should consider symptoms, calcium levels, bone health, medical conditions and whether the result was taken during winter or summer.

Why do laboratories use nmol/L?

UK laboratories generally report vitamin D in nanomoles per litre, written as nmol/L. Some overseas websites use nanograms per millilitre, or ng/mL.

The two units are not numerically identical, so values should not be compared without conversion.

Other blood tests

When deficiency is significant or symptoms suggest osteomalacia, clinicians may also check:

• calcium;
• phosphate;
• alkaline phosphatase;
• parathyroid hormone;
• kidney function;
• liver function;
• magnesium;
• full blood count;
• coeliac screening where indicated.

Our guide to calcium and bone-profile blood-test results explains how calcium, phosphate and alkaline phosphatase are interpreted together.

Can deficiency be diagnosed from symptoms alone?

No. Fatigue, aches and weakness are too non-specific. Treatment with a standard preventive supplement may be reasonable for many people, but a diagnosis of clinically important deficiency or osteomalacia usually needs appropriate assessment.

How is vitamin D deficiency treated?

Treatment depends on the result, symptoms, age, cause and whether there is associated low calcium or bone disease.

The main forms of treatment are:

• a higher-dose loading course for confirmed deficiency where clinically appropriate;
• a lower long-term maintenance dose;
• adequate calcium intake;
• treatment of the underlying cause;
• specialist management when kidney disease, malabsorption or severe symptoms are present.

Loading treatment

Adults with significant deficiency may be prescribed a loading course of colecalciferol. The aim is to replenish vitamin D stores over several weeks.

NHS regimens can provide a total dose of up to approximately 300,000 international units, divided over several weeks rather than taken all at once without supervision.

Examples used in clinical practice may include 50,000 IU weekly for six weeks or another equivalent schedule. The exact product and regimen vary locally.

High-dose treatment should be taken exactly as prescribed. A weekly capsule accidentally taken every day can cause vitamin D toxicity.

Maintenance treatment

After a loading course, people who remain at risk may be advised to take a maintenance dose. NHS prescribing information commonly describes doses around 800 to 2,000 IU daily after treatment, depending on individual circumstances.

This is different from the standard 400 IU prevention dose recommended to the general population.

Treatment without a loading dose

Some people with mild deficiency, no significant symptoms and no urgent bone concerns may be managed with a regular daily dose rather than a loading course.

The clinician should consider:

• the measured level;
• symptoms;
• fracture or osteomalacia risk;
• pregnancy;
• kidney function;
• malabsorption;
• likelihood of taking the treatment consistently.

Calcium

Vitamin D allows calcium to be absorbed, but the diet must also provide enough calcium.

Sources include:

• milk, yoghurt and cheese;
• calcium-fortified plant drinks;
• calcium-set tofu;
• tinned sardines or salmon with edible bones;
• some green vegetables;
• fortified foods.

Calcium supplements are not automatically needed. Excessive supplementation may be unsuitable for people with kidney stones, high blood calcium or certain kidney conditions.

Treating malabsorption or kidney disease

Standard doses may not be enough when vitamin D is poorly absorbed. Specialist advice may be needed regarding dose, formulation and monitoring.

People with advanced kidney disease may need activated forms of vitamin D because damaged kidneys cannot complete the normal conversion process efficiently.

How should vitamin D be taken?

Vitamin D is fat soluble. Taking it with a meal may improve absorption, especially if the meal contains some fat.

The most important factor is consistency. Follow the instructions for the specific product because daily, weekly and monthly formulations can look similar while containing very different strengths.

How can vitamin D deficiency be prevented?

Prevention involves a combination of sensible sunlight exposure, food and supplements.

UK supplement advice

UK public health advice recommends that adults and children aged over 4 consider taking 10 micrograms, or 400 IU, of vitamin D daily from October to early March.

Year-round supplementation is advised for people who may not make enough vitamin D from sunlight, including those who:

• are rarely outdoors;
• are frail or housebound;
• live in a care home;
• usually cover most of their skin outside;
• have dark skin.

This is prevention advice for the general population. It is not necessarily enough to treat confirmed deficiency.

Sunlight

During spring and summer, regular short periods outdoors with some skin exposed can help the body produce vitamin D.

There is no single safe exposure time that applies to everyone. Production depends on:

• skin tone;
• time of day;
• cloud cover;
• location;
• age;
• amount of skin exposed.

The skin should never be allowed to burn. People with a history of skin cancer, photosensitivity or medicines that increase sun sensitivity should follow specialist advice.

Food sources

Foods containing vitamin D include:

• oily fish such as salmon, sardines, herring and mackerel;
• egg yolks;
• liver in limited amounts, although liver should be avoided during pregnancy because of its high vitamin A content;
• fortified breakfast cereals;
• fortified plant drinks;
• some fortified spreads and yoghurts.

Diet contributes, but it is difficult for many people to obtain 10 micrograms every day from food alone.

Choosing a supplement

Check the label for:

• the amount per dose;
• whether it is measured in micrograms or IU;
• whether the product contains vitamin D2 or D3;
• whether other supplements already contain vitamin D;
• whether it is suitable for children, pregnancy or a vegan diet.

One microgram of vitamin D equals 40 IU. Therefore:

• 10 micrograms equals 400 IU;
• 25 micrograms equals 1,000 IU;
• 100 micrograms equals 4,000 IU.

Can you take too much vitamin D?

Yes. Vitamin D is stored in the body, and excessive supplementation over time can cause toxicity.

Too much vitamin D raises calcium levels in the blood, a condition called hypercalcaemia.

Possible symptoms include:

• nausea and vomiting;
• poor appetite;
• constipation;
• excessive thirst;
• frequent urination;
• weakness;
• confusion;
• abdominal pain;
• kidney stones;
• an abnormal heart rhythm in severe cases.

Long-term hypercalcaemia can damage the kidneys and heart and may weaken bones.

What is the safe upper limit?

Unless a clinician has prescribed a higher treatment dose, adults and children aged 11 or over should not generally take more than 100 micrograms, or 4,000 IU, daily.

Prescribed loading courses may temporarily exceed this daily amount because they are given according to a controlled schedule.

Who needs particular caution?

Speak to a clinician before taking higher-dose vitamin D if you have:

• high calcium levels;
• kidney stones;
• significant kidney disease;
• sarcoidosis;
• some lymphomas;
• hyperparathyroidism;
• another condition affecting vitamin D or calcium metabolism.

People with these conditions may become hypercalcaemic at doses that would normally be safe for others.

Avoid accidental double dosing

Vitamin D may be present in:

• multivitamins;
• calcium tablets;
• pregnancy supplements;
• cod-liver oil;
• prescribed osteoporosis products;
• individual vitamin D supplements.

Add the total from every product rather than considering each one separately.

How long does recovery take?

Blood levels usually begin to rise during treatment, but symptoms may take longer to improve.

Muscle weakness

Muscle strength may improve gradually over weeks or months. Recovery can take longer when deficiency has been severe, the person is older or physical activity has been limited for a long time.

Bone pain and osteomalacia

Bone pain may begin improving within weeks, but complete remineralisation of bone can take several months.

A person with severe osteomalacia may need physiotherapy, falls assessment and investigation for fractures as well as vitamin D treatment.

Fatigue

If vitamin D deficiency is contributing to tiredness, improvement may be gradual. Continued fatigue should prompt consideration of other causes rather than repeated high-dose supplementation without review.

When is the blood test repeated?

Repeat testing is not always needed after ordinary prevention advice. It may be considered when:

• symptoms continue;
• deficiency was severe;
• malabsorption is suspected;
• the person has taken treatment inconsistently;
• there is chronic kidney or liver disease;
• a specialist needs to confirm response.

Testing too soon may not provide useful information because the level and bone response take time to stabilise.

What if the level stays low?

A clinician may review:

• whether the correct dose was taken;
• whether daily and weekly instructions were confused;
• whether the supplement contains the stated strength;
• malabsorption;
• obesity;
• medicines affecting vitamin D;
• kidney or liver disease;
• the need for specialist treatment.

Vitamin D, osteoporosis and fractures

Vitamin D deficiency and osteoporosis are related but not identical.

Osteomalacia means existing bone is not being mineralised properly, usually because of severe vitamin D deficiency or another disturbance in mineral metabolism.

Osteoporosis means bone density and internal structure have deteriorated, increasing fracture risk.

A person can have:

• vitamin D deficiency without osteoporosis;
• osteoporosis with a normal vitamin D level;
• both conditions at the same time.

Why vitamin D is checked before osteoporosis treatment

Some bone-strengthening medicines can lower blood calcium, particularly if vitamin D deficiency is already present.

Clinicians may therefore check and correct vitamin D and calcium before treatment such as intravenous bisphosphonates or denosumab.

Can vitamin D alone treat osteoporosis?

No. Vitamin D supports bone health and may correct osteomalacia, but it is not usually enough to reduce fracture risk in someone with established high-risk osteoporosis.

Bone-strengthening medicine, falls prevention, resistance exercise and adequate calcium may also be needed.

Our guide to DEXA scans and bone-density results explains how osteoporosis is assessed using T-scores, Z-scores and overall fracture risk.

Can vitamin D prevent falls?

Correcting genuine deficiency may improve muscle function and reduce falls risk in some deficient older adults. Taking very high doses does not provide additional protection and may be harmful.

Falls prevention should also address strength, balance, eyesight, footwear, medicines and hazards in the home.

When should you contact a doctor?

Arrange a GP appointment if you have symptoms or risk factors suggesting clinically important deficiency.

Speak to a GP if you have:

• persistent muscle weakness;
• difficulty climbing stairs or rising from a chair;
• ongoing widespread bone pain;
• repeated falls;
• a fragility fracture;
• a condition causing malabsorption;
• previous bariatric surgery;
• chronic kidney or liver disease;
• symptoms that continue despite taking a standard supplement;
• concern about giving a supplement to a baby or child.

Request prompt assessment if:

• walking is becoming difficult;
• bone pain is severe or localised;
• you may have fractured a bone;
• you have significant weakness with abnormal calcium results;
• a baby or child has poor growth, bone changes or delayed development.

Seek urgent medical help for:

• seizures;
• severe muscle spasms;
• marked confusion;
• collapse;
• a new irregular heartbeat;
• severe vomiting, thirst and frequent urination after taking high-dose supplements.

These symptoms can indicate severe low calcium or vitamin D toxicity rather than ordinary mild deficiency.

Frequently asked questions about vitamin D deficiency

What is the main symptom of vitamin D deficiency?

There is no single defining symptom. Many people have no symptoms, while others experience muscle weakness, bone pain or general aches. Fatigue alone is not specific.

Can low vitamin D make you tired?

It may contribute to fatigue in some people, but anaemia, thyroid disease, sleep problems, vitamin B12 deficiency and many other conditions are also common causes.

Can vitamin D deficiency cause joint pain?

Deficiency can cause widespread bone and muscle pain that may be described as joint pain. Pain isolated to one swollen or stiff joint is more likely to have another explanation.

Can low vitamin D cause back pain?

Osteomalacia can cause pain in the lower back, pelvis and ribs. Back pain is extremely common, however, and is more often caused by muscles, joints, discs or age-related spinal changes.

Can vitamin D deficiency cause hair loss?

Some studies have found associations between low vitamin D and certain hair-loss conditions, but hair loss is not a reliable diagnostic symptom. Iron deficiency, thyroid disease, genetics and scalp disorders should also be considered.

Can vitamin D deficiency cause depression?

Low vitamin D and depression can occur together, but it is not clear that deficiency is the sole cause in most cases. Vitamin D treatment should not replace appropriate mental health assessment and care.

Can vitamin D deficiency cause pins and needles?

Pins and needles are not among the most characteristic symptoms. Vitamin B12 deficiency, nerve compression, diabetes, anxiety and neurological conditions are more common explanations.

Can low vitamin D cause dizziness?

Dizziness is not a specific symptom. It may accompany muscle weakness or general illness, but low blood pressure, anaemia, inner-ear conditions and heart problems should also be considered.

What level is considered vitamin D deficient?

NICE guidance generally describes a 25(OH)D level below 25 nmol/L as deficient. Levels from 25 to 50 nmol/L may be inadequate for some people, while levels above 50 nmol/L are sufficient for most.

Do I need a vitamin D blood test?

Not necessarily. Routine testing is not recommended for every healthy person. Testing is more useful when symptoms, bone disease, malabsorption or another clinical factor makes the result likely to change management.

Should everyone in the UK take vitamin D?

Everyone aged over 4 is advised to consider 10 micrograms daily during autumn and winter. People with little sunlight exposure or dark skin should consider taking this amount throughout the year.

Is 10 micrograms enough to treat deficiency?

Usually not. Ten micrograms, or 400 IU, is a prevention dose. Confirmed deficiency may require a higher prescribed loading and maintenance regimen.

Is 1,000 IU of vitamin D safe?

For most adults, 1,000 IU daily is below the general upper limit of 4,000 IU. People with high calcium, kidney disease, sarcoidosis or related conditions should seek individual advice.

Can I take 5,000 IU every day?

Five thousand IU exceeds the usual general upper daily limit of 4,000 IU. It should not be taken long term unless a clinician has recommended and is monitoring it.

Should vitamin D be taken with food?

It can be taken with food, and absorption may be improved when the meal contains some fat. Follow the instructions for the specific product.

Is morning or evening better?

There is no strong evidence that one time is best. Choose a consistent time that helps you remember the dose.

How long does vitamin D take to work?

Blood levels begin rising during treatment, but muscle weakness and bone pain may take weeks or months to improve.

Can vitamin D deficiency be cured permanently?

The level can usually be corrected, but deficiency may return if the underlying risk remains. Long-term supplementation is often needed for people with limited sunlight, dark skin, malabsorption or another ongoing risk factor.

Can vitamin D supplements cause kidney stones?

Ordinary recommended doses do not commonly cause stones. Excessive vitamin D can raise calcium and increase kidney risk, particularly when combined with unnecessary high-dose calcium.

Is vitamin D3 better than D2?

Both can treat deficiency, although vitamin D3 is commonly used and may maintain levels more effectively in some dosing regimens. Vegan D2 and lichen-derived D3 are available.

Can you get enough vitamin D from food?

It is difficult for many people because relatively few foods contain substantial amounts. Fortified foods help, but supplements remain important during UK autumn and winter.

Can I get vitamin D through a window?

Ordinary window glass blocks most ultraviolet B radiation needed for vitamin D production. Sitting in sunlight indoors therefore does not provide the same effect as being outside.

Do sunbeds help vitamin D levels?

Sunbeds are not recommended as a vitamin D source. They increase the risk of skin damage and skin cancer. Supplements provide a safer and more controlled dose.

Can vitamin D prevent colds, flu or COVID-19?

Vitamin D supports normal immune function, but routine high-dose supplementation should not be promoted as a treatment or guaranteed prevention for respiratory infections. The clearest established benefit of current UK advice is supporting bone and muscle health.