Preparing for vitamin D

Overview

A vitamin D test is a blood test that measures the level of vitamin D in your body. Vitamin D helps your body absorb calcium and keeps your bones, muscles, and immune system healthy. The test is often done to check for a vitamin D deficiency (too little vitamin D) or to monitor treatment.

Vitamin D testing is fairly common, especially if you have symptoms of deficiency or have risk factors like limited sun exposure, darker skin, or certain medical conditions.

Vitamin D deficiency can affect anyone, but it is more common in people who get little sun, have darker skin, are older, are pregnant or breastfeeding, have obesity, or have conditions that affect nutrient absorption.

Symptoms

Common symptoms

• Feeling very tired or weak
• Bone pain or tenderness
• Muscle aches or cramps
• Mood changes, such as feeling low or depressed

Symptoms in children

• Slow growth
• Soft or bent bones (called rickets)
• Muscle weakness or delay in walking

Symptoms in older adults

• Increased risk of falls and fractures
• Bone pain, especially in the lower back or hips
• Muscle weakness and difficulty getting up from a chair

Causes

Main causes

• Not getting enough sunlight on your skin
• Low dietary intake of vitamin D (found in fatty fish, egg yolks, and fortified foods)
• Your body not absorbing vitamin D properly (due to gut conditions like Crohn's or celiac disease)

Risk factors

• Living in northern latitudes or areas with little sun
• Having naturally dark skin (more melanin reduces vitamin D production)
• Being older (skin makes less vitamin D with age)
• Being overweight or obese
• Taking certain medications that affect vitamin D metabolism (such as some seizure drugs)
• Having kidney or liver disease

When to see a doctor

See a doctor urgently if:

• If you have severe bone pain that doesn't go away
• If you have muscle spasms or seizures (very rare, but possible with extremely low vitamin D)

Book a routine appointment if:

• If you have ongoing tiredness, bone pain, or muscle weakness
• If you have a condition that puts you at risk for deficiency (like celiac, inflammatory bowel disease, or after weight-loss surgery)
• If you are over 65 and fall often
• If you are pregnant or breastfeeding and concerned about your vitamin D levels

Diagnosis

A vitamin D test is a simple blood test. Your doctor will take a sample of blood from a vein in your arm and send it to a lab to measure your 25-hydroxyvitamin D level.

Tests that may be done

• 25-hydroxyvitamin D blood test (the main test)
• Sometimes a calcium or phosphate blood test may also be done

What to expect at your appointment

You will have blood drawn, which takes just a few minutes. You don't need to stop eating or drinking beforehand. However, tell your doctor if you take biotin supplements, because biotin can interfere with some lab tests. The results usually come back in a few days to a week.

Treatment

If your test shows low vitamin D, your doctor will recommend ways to raise your levels. This may include spending more time in sunlight, eating vitamin D-rich foods, or taking supplements. Treatment is usually simple and effective.

Self-care at home

• Spend 10–30 minutes in the sun several times a week (without sunscreen) if safe for your skin type and location. Be careful not to burn.
• Eat foods rich in vitamin D: oily fish (salmon, mackerel), egg yolks, fortified milk, and fortified cereals.
• Consider a vitamin D supplement if advised by your doctor – follow their dosage instructions.

Medical treatments

For significant deficiency, your doctor may prescribe high-dose vitamin D supplements for a short time to quickly raise your levels. After that, a lower daily dose may be recommended to keep your levels healthy. Always take supplements only as advised by a healthcare professional.

When is surgery considered?

Surgery is not used to treat vitamin D deficiency.

Living with this condition

Once you know your vitamin D level and start any recommended changes, living with vitamin D deficiency is manageable. You may need to be more mindful of sun exposure and diet, and take a supplement if prescribed. Your doctor will likely retest your blood after a few months to see if your levels have improved.

Lifestyle tips

• Get regular, safe sun exposure – even 15 minutes a day can help.
• Consider keeping a food diary to track vitamin D-rich foods.
• If you take a supplement, set a daily reminder so you don't forget.

Diet and exercise

Eat a balanced diet with vitamin D-rich foods. Weight-bearing exercise like walking or lifting weights can help strengthen bones. Your doctor may also recommend calcium if your vitamin D is low, as the two work together for bone health.

Mental health and emotional wellbeing

Low vitamin D has been linked to low mood and depression in some studies. Treating the deficiency may help improve your mood and energy levels. If you are feeling very down, talk to your doctor or a mental health professional. For immediate crisis support, contact your local crisis helpline or emergency services.

Prevention

In many cases, vitamin D deficiency can be prevented with adequate sun exposure, a balanced diet, and supplements if needed. However, some people with certain medical conditions may still become deficient despite prevention efforts.

Screening programmes

Routine screening for vitamin D deficiency is not recommended for everyone. Your doctor may suggest testing if you have symptoms or risk factors. You can ask your doctor if testing is right for you.

Complications

If left untreated

• Soft, weak, or deformed bones (osteomalacia in adults, rickets in children)
• Increased risk of fractures
• Muscle weakness and falls
• Possible links to weakened immune function, depression, and other chronic conditions

Long-term outlook

The outlook for vitamin D deficiency is very good. With proper treatment—whether through sunlight, diet, or supplements—most people can raise their vitamin D levels and reduce or reverse symptoms. Early detection and treatment prevent most complications.

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