Vitamin D Deficiency: Symptoms, Causes, Diagnosis and Safe Treatment

Vitamin D is an essential nutrient that helps your body absorb calcium and phosphorus, maintain strong bones and support normal muscle function. Your body can produce vitamin D when your skin is exposed to ultraviolet B (UVB) rays from sunlight. You can also obtain it from certain foods and supplements.

Despite living in a sunny country like India, many people may have inadequate vitamin D levels. Spending most of the day indoors, covering most of the skin, having limited dietary sources and certain medical conditions can all contribute.

Vitamin D deficiency can develop without obvious symptoms. When it becomes severe or prolonged, it can weaken bones and cause muscle problems.

In this guide, you’ll learn about the common symptoms, causes and risk factors of vitamin D deficiency, how doctors diagnose it, which foods provide vitamin D and how to supplement safely.

1. What Is Vitamin D and Why Does Your Body Need It?

Vitamin D is a fat-soluble vitamin that plays an important role in maintaining healthy bones and muscles.

Unlike many nutrients, your body can produce vitamin D when your skin receives sufficient UVB radiation from sunlight.

There are two main forms:

• Vitamin D2 (ergocalciferol): Found in some mushrooms and plant-based fortified foods.
• Vitamin D3 (cholecalciferol): Produced in the skin through sunlight exposure and found in some animal-derived foods and supplements.

Both forms can increase vitamin D levels in the blood.

Important functions of vitamin D

Helps absorb calcium and phosphorus

Vitamin D helps your intestines absorb calcium and phosphorus from food. These minerals are essential for healthy bones and teeth.

Maintains bone strength

Adequate vitamin D helps prevent bones from becoming soft or weak. Severe deficiency can cause rickets in children and osteomalacia in adults.

Supports muscle function

Vitamin D is involved in normal muscle function. Severe deficiency can cause muscle weakness and discomfort.

Contributes to normal immune function

Vitamin D plays a role in regulating immune-system activity. However, taking extra vitamin D does not guarantee protection against infections or chronic diseases.

Vitamin D is important, but more is not necessarily better. Maintaining an appropriate level is the goal.

2. What Causes Vitamin D Deficiency?

Vitamin D deficiency can develop when the body does not produce enough vitamin D, dietary intake is inadequate, or the body cannot absorb or process it properly.

Several factors can contribute.

1. Limited sunlight exposure

Sunlight is an important natural source of vitamin D.

People who spend most of their time indoors, work night shifts or have limited outdoor activity may produce less vitamin D through their skin.

2. Darker skin pigmentation

Melanin, the pigment responsible for skin colour, reduces the skin’s production of vitamin D from UVB exposure.

People with darker skin may therefore need more UVB exposure than people with lighter skin to produce similar amounts.

3. Covering most of the skin

Clothing that covers most of the body can reduce the amount of skin exposed to UVB rays.

This may contribute to low vitamin D levels, particularly when combined with limited outdoor activity and inadequate dietary intake.

4. Inadequate dietary intake

Only a small number of foods naturally contain significant amounts of vitamin D.

People who rarely eat fatty fish, eggs, fortified foods or other vitamin D sources may have difficulty meeting their requirements through diet alone.

5. Obesity

People with obesity are more likely to have lower circulating vitamin D levels. Vitamin D is distributed into body fat, which may affect its availability in the bloodstream.

6. Digestive disorders

Certain medical conditions can interfere with vitamin D absorption.

Examples include:

• Coeliac disease
• Crohn’s disease
• Ulcerative colitis in some circumstances
• Conditions involving fat malabsorption
• Certain gastrointestinal surgeries

7. Liver and kidney diseases

The liver and kidneys help convert vitamin D into forms that the body can use.

Chronic liver or kidney disease can interfere with this process and contribute to vitamin D problems.

8. Certain medications

Some medicines can affect vitamin D absorption or metabolism.

Examples include certain anti-seizure medicines, glucocorticoids and some weight-loss or fat-absorption medicines.

If you take long-term medication, ask your doctor whether it could affect your vitamin D status. Do not stop prescribed medication on your own.

3. Ten Possible Symptoms of Vitamin D Deficiency

Vitamin D deficiency does not always cause noticeable symptoms. When symptoms occur, they are often nonspecific and can overlap with many other medical conditions.

The following signs may warrant medical assessment, particularly when persistent or accompanied by other symptoms.

1. Persistent bone pain

Vitamin D is essential for calcium absorption and bone mineralisation.

Severe or prolonged deficiency can cause osteomalacia in adults, which may produce deep bone pain or tenderness.

Pain can occur in areas such as the back, hips, pelvis and legs.

2. Muscle weakness

Vitamin D plays a role in normal muscle function.

Severe deficiency may cause muscle weakness, difficulty climbing stairs or trouble getting up from a seated position.

3. Frequent muscle aches

Some people with significant vitamin D deficiency experience muscle discomfort or tenderness.

However, muscle aches are common and can have many causes, including overuse, medication effects and other nutritional deficiencies.

4. Fatigue and tiredness

Persistent tiredness is sometimes reported by people with low vitamin D levels.

However, fatigue alone is not a reliable way to identify deficiency. Anaemia, thyroid disorders, sleep problems, stress and other medical conditions can also cause fatigue.

5. Bone tenderness

Long-standing deficiency can affect bone mineralisation and may cause tenderness.

If you experience persistent or unexplained bone pain, consult a healthcare professional rather than assuming vitamin D is the cause.

6. Difficulty walking or climbing stairs

Significant muscle weakness, particularly in the hips and thighs, may make everyday movements difficult.

People with severe deficiency may struggle to walk, climb stairs or stand up from a low chair.

7. Increased risk of bone fractures

Long-term vitamin D deficiency can contribute to poor bone mineralisation.

In adults, severe deficiency may cause osteomalacia and increase the risk of fractures. Fracture risk also depends on age, bone density, falls and other medical factors.

8. Delayed growth or bone development in children

Vitamin D is particularly important during childhood because bones are growing rapidly.

Severe deficiency can cause rickets, which may lead to:

• Bowed legs
• Bone pain
• Delayed growth
• Poor bone development
• Muscle weakness

Children with possible signs of rickets need prompt medical assessment.

9. Changes in mood

Some studies have found an association between low vitamin D levels and depression.

However, this does not mean vitamin D deficiency is the cause of depression, or that supplementation is an established treatment for depression in everyone.

Persistent low mood deserves appropriate medical attention.

10. Delayed recovery from muscle or bone problems

Vitamin D is involved in normal bone and muscle function. Severe deficiency can contribute to weakness and impaired bone mineralisation.

However, slow wound healing or recovery is not a specific symptom that can diagnose vitamin D deficiency.

Important: These symptoms are not proof of low vitamin D. A medical assessment is needed to identify the actual cause.

4. Who Is at Greater Risk of Vitamin D Deficiency?

Although vitamin D deficiency can affect anyone, certain groups have a higher likelihood of developing inadequate levels.

Infants and young children

Breast milk alone generally does not provide enough vitamin D to meet an infant’s requirements. Infants may need supplementation according to paediatric guidance.

Children who have limited dietary intake or little outdoor activity may also be at risk.

Older adults

As people age, their skin becomes less efficient at producing vitamin D from sunlight.

Older adults may also spend less time outdoors and have a higher likelihood of medical conditions that affect vitamin D status.

Pregnant and breastfeeding women

Vitamin D is important for maternal and infant bone health.

Pregnant women should discuss their vitamin D intake with their healthcare professional and follow appropriate prenatal supplementation guidance.

People with darker skin

Higher melanin levels reduce the skin’s production of vitamin D from UVB exposure.

People with darker skin pigmentation may therefore be more vulnerable when sunlight exposure and dietary intake are limited.

People who spend most of their time indoors

Office workers, night-shift employees and people with limited mobility may receive less direct sunlight.

People with obesity or digestive disorders

Obesity and conditions that interfere with fat absorption can affect vitamin D status.

If you belong to a higher-risk group, discuss your individual nutritional needs with a healthcare professional.

5. How Is Vitamin D Deficiency Diagnosed?

Symptoms alone cannot confirm vitamin D deficiency.

The commonly used blood test is called 25-hydroxyvitamin D, also written as 25(OH)D.

It measures the main circulating form of vitamin D and is generally the preferred test for assessing vitamin D status when testing is clinically indicated.

Understanding vitamin D blood-test results

Laboratory interpretation varies, and there is no universally agreed blood concentration that defines the ideal level for every health outcome.

The US National Institutes of Health Office of Dietary Supplements provides the following general interpretation:

Blood level	General interpretation
Below 12 ng/mL	Associated with vitamin D deficiency
12 to below 20 ng/mL	Generally considered inadequate for some people
20 ng/mL or above	Generally adequate for bone and overall health in most healthy people
Above 50 ng/mL	May be associated with adverse effects, particularly at higher levels

These are general reference points, not a personalised treatment target. Your doctor should interpret the result alongside your health, age, symptoms and medical history.

Do healthy adults need regular vitamin D testing?

Not necessarily.

The 2024 Endocrine Society guideline suggests against routine vitamin D testing in generally healthy adults who do not have an established medical reason for testing.

Testing may be appropriate when a person has symptoms, suspected bone disease, certain medical conditions or other specific clinical indications.

Your doctor may also request additional tests, such as calcium, phosphate, alkaline phosphatase or kidney function tests, depending on the situation.

6. How Can You Improve Vitamin D Levels Naturally?

There are three main ways to maintain adequate vitamin D:

1. Sensible sunlight exposure.
2. Foods containing vitamin D.
3. Supplements when needed.

The right approach depends on your health, diet, lifestyle and medical requirements.

1. Get sensible sunlight exposure

When UVB rays reach exposed skin, your body can produce vitamin D.

However, there is no single sunlight schedule that works for everyone.

Vitamin D production depends on:

• Skin pigmentation
• Age
• Time of day
• Season
• Geographic location
• Air pollution
• Clothing
• Amount of exposed skin

People with darker skin may need more UVB exposure to produce the same amount of vitamin D as people with lighter skin.

Do not deliberately tan or allow your skin to burn in an attempt to increase vitamin D. Excessive UV exposure increases the risk of skin damage and skin cancer.

Follow appropriate sun-protection advice and discuss vitamin D needs with a healthcare professional if you have limited safe sunlight exposure.

2. Include vitamin D-rich foods

Diet can help maintain vitamin D intake, although relatively few foods naturally contain substantial amounts.

Useful sources include:

Fatty fish

• Salmon
• Sardines
• Mackerel
• Tuna

Egg yolks

Egg yolks provide some vitamin D, although the amount varies.

UV-exposed mushrooms

Certain mushrooms exposed to ultraviolet light can contain vitamin D2. Check the product information where available.

Fortified foods

Some products are fortified with vitamin D, including selected milk products, breakfast cereals and plant-based alternatives.

Check food labels because not all products contain added vitamin D.

3. Choose a balanced diet

A balanced diet supports overall bone health.

Include foods containing calcium, protein and other nutrients.

Examples include:

• Milk and yoghurt
• Fortified plant-based milk
• Ragi
• Sesame seeds
• Green leafy vegetables
• Pulses and beans
• Fish and eggs, if part of your diet

Remember that calcium and vitamin D perform different but complementary roles. Consuming calcium alone does not correct vitamin D deficiency.

7. Vitamin D Supplements: D2 vs D3

When sunlight and food do not provide sufficient vitamin D, supplementation may be appropriate.

The two common forms are:

Vitamin D2 (ergocalciferol)

This form is found in some plant-based and fortified products and is also available as a supplement.

Vitamin D3 (cholecalciferol)

This form is produced in the skin through sunlight exposure and is found in some animal-derived foods and supplements.

Both can increase vitamin D levels. Vitamin D3 may raise and maintain blood levels more effectively in some circumstances.

The appropriate choice depends on your individual requirements, diet and medical history.

Should you take vitamin D supplements every day?

Some people benefit from regular supplementation, particularly when dietary intake is inadequate or they have specific risk factors.

The recommended intake for generally healthy people is different from the dose used to treat a confirmed deficiency.

Do not assume that a high-dose supplement is necessary simply because you feel tired or spend little time outdoors.

8. Recommended Daily Vitamin D Intake

The US National Institutes of Health lists the following recommended dietary allowances:

Age or life stage	Daily recommended intake
Birth to 12 months	400 IU
Children 1–18 years	600 IU
Adults 19–70 years	600 IU
Adults over 70 years	800 IU
Pregnancy and breastfeeding	600 IU

These are general dietary reference intakes, not treatment doses for people with confirmed deficiency. Local recommendations and individual medical needs may differ.

What is the safe upper limit?

For most adults aged 19 and older, the US tolerable upper intake level is 4,000 IU (100 micrograms) per day from all sources.

This is a safety limit, not a recommended daily target.

A doctor may prescribe higher doses for a limited period to treat confirmed deficiency, but this should be medically supervised.

9. Can You Take Too Much Vitamin D?

Yes. Excessive vitamin D supplementation can cause toxicity.

Because vitamin D increases calcium absorption, excessive amounts can result in high calcium levels in the blood, a condition called hypercalcaemia.

Possible symptoms include:

• Nausea and vomiting
• Loss of appetite
• Constipation
• Unusual thirst
• Frequent urination
• Muscle weakness
• Confusion
• Kidney stones or kidney damage in severe cases

In serious situations, vitamin D toxicity can lead to kidney failure, abnormal heart rhythms and other complications.

Toxicity is usually caused by excessive supplement intake rather than ordinary sunlight exposure or normal food consumption.

Never take repeated high-dose vitamin D sachets, capsules or injections without medical advice.

If you are prescribed a high-dose treatment course, follow the exact schedule and duration provided by your doctor.

10. Vitamin D During Pregnancy and Childhood

Vitamin D is important during periods of rapid bone growth and development.

During pregnancy

Vitamin D supports calcium absorption and the development of the baby’s bones.

Pregnant women should review their prenatal vitamin and dietary intake with their healthcare professional.

Some pregnancy guidelines recommend supplementation, but the dose and need for additional vitamin D depend on individual circumstances and local medical guidance.

Avoid taking extra high-dose supplements without discussing them with your obstetrician.

For infants and children

Adequate vitamin D is essential for normal bone development.

Infants who receive only breast milk may need vitamin D supplementation because breast milk generally does not contain enough to meet their requirements.

Children with restricted diets, limited sun exposure or medical conditions affecting absorption may also need assessment.

Parents should consult a paediatrician before giving supplements or changing a child’s dosage.

11. Myths and Facts About Vitamin D

Myth 1: Living in a sunny country means you cannot become deficient.

Fact: People can have low vitamin D levels even in sunny countries. Indoor lifestyles, skin pigmentation, clothing, dietary intake and other factors influence vitamin D production.

Myth 2: Fatigue always means vitamin D deficiency.

Fact: Fatigue has many possible causes. A vitamin D test is not a substitute for a proper medical assessment.

Myth 3: More vitamin D is always better.

Fact: Excessive supplementation can cause toxicity and dangerously high calcium levels.

Myth 4: You must spend hours in the sun to get vitamin D.

Fact: Individual sunlight requirements vary. Deliberate prolonged exposure and sunburn are not safe ways to treat deficiency.

Myth 5: Vitamin D supplements prevent every infection.

Fact: Vitamin D is involved in normal immune function, but supplements should not be treated as guaranteed protection against infections.

Myth 6: Everyone should get a vitamin D blood test every year.

Fact: Current Endocrine Society guidance does not recommend routine testing for generally healthy adults without an established reason.

12. When Should You Consult a Doctor?

Consider medical assessment if you experience:

• Persistent unexplained bone pain.
• Ongoing muscle weakness.
• Difficulty walking or climbing stairs.
• Repeated fractures or suspected bone disease.
• Symptoms of rickets in a child.
• A medical condition that affects nutrient absorption.
• A known low vitamin D result.
• Symptoms that develop after taking high-dose supplements.

Seek urgent medical advice if you develop severe vomiting, confusion, marked weakness, dehydration or other concerning symptoms after taking excessive vitamin D.

A healthcare professional can determine whether testing, dietary changes or supplementation is appropriate.

Conclusion: Maintain Healthy Vitamin D Levels Safely

Vitamin D plays an essential role in calcium absorption, bone strength and normal muscle function. Inadequate levels can contribute to weak bones, muscle weakness and, in severe cases, conditions such as rickets and osteomalacia.

Spending sensible time outdoors, including vitamin D-rich or fortified foods in your diet and using supplements when medically appropriate can help maintain healthy levels.

However, vitamin D deficiency cannot be diagnosed by symptoms alone. Fatigue, mood changes and muscle aches can have many different causes.

Avoid unnecessary high-dose supplements and do not assume that taking more vitamin D will provide extra health benefits.

The best approach is to understand your individual needs, follow reliable medical advice and maintain a balanced lifestyle.

Frequently Asked Questions

1. What are the most common symptoms of vitamin D deficiency?

Possible symptoms include bone pain, muscle weakness, muscle aches and difficulty walking. However, many people have no obvious symptoms, and these signs can have other causes.

2. Can vitamin D deficiency cause tiredness?

Fatigue is sometimes reported by people with low vitamin D levels, but it is not specific to deficiency. Other causes such as anaemia, thyroid problems and poor sleep should also be considered.

3. Can you get vitamin D deficiency in India?

Yes. Despite abundant sunlight in many parts of India, people can develop low vitamin D levels because of indoor lifestyles, skin pigmentation, clothing, dietary habits and medical conditions.

4. Which foods are highest in vitamin D?

Fatty fish such as salmon, sardines and mackerel are useful sources. Egg yolks, UV-exposed mushrooms and vitamin D-fortified foods can also contribute.

5. Is morning sunlight enough for vitamin D?

There is no universal time of day or number of minutes that guarantees sufficient vitamin D production. UVB intensity, skin pigmentation, location, season and exposed skin all matter.

6. How long does it take to correct vitamin D deficiency?

It depends on how low the level is, the treatment prescribed, absorption and individual health. Some people need several weeks or months of treatment, followed by reassessment when clinically appropriate.

7. Is vitamin D2 or D3 better?

Both forms can increase vitamin D levels. Vitamin D3 may raise blood levels more effectively in some people, but the appropriate form depends on individual needs.

8. Can vitamin D deficiency cause hair loss?

Some studies have found associations between low vitamin D levels and certain hair-loss conditions. However, hair loss has many possible causes, and vitamin D deficiency cannot be diagnosed from hair shedding alone.

9. Can vitamin D deficiency affect bones?

Yes. Severe or prolonged deficiency can impair bone mineralisation. In children it can cause rickets, while in adults it can cause osteomalacia.

10. Is it safe to take vitamin D supplements daily?

Daily supplementation can be appropriate for some people, but the correct amount depends on age, diet, medical conditions and individual requirements. Avoid exceeding recommended limits without medical supervision.

11. Can vitamin D be obtained from food alone?

Some people can obtain adequate vitamin D through food and fortified products, but this can be difficult because relatively few foods naturally contain substantial amounts. Individual needs vary.

12. Should everyone get a vitamin D blood test?

No. Routine testing is not recommended for all healthy adults. Testing is more appropriate when there is a specific clinical reason, such as suspected deficiency or a condition affecting vitamin D metabolism.

Medical Disclaimer

This article is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Vitamin D requirements vary according to age, health status and individual circumstances. Consult a qualified healthcare professional before starting high-dose supplements, changing medication or treating a suspected deficiency.

References and Further Reading

1. National Institutes of Health, Office of Dietary Supplements – Vitamin D: Fact Sheet for Health Professionals.
2. Endocrine Society – Vitamin D for the Prevention of Disease: Clinical Practice Guideline.
3. NHS – Vitamin D.
4. MedlinePlus – Vitamin D Deficiency.
5. National Institute of Arthritis and Musculoskeletal and Skin Diseases – Osteomalacia.