Lab results explained
Low vitamin D level: what it means
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Short answer: A low vitamin D level means your body has less of the vitamin it needs to absorb calcium and keep bones strong. Below 20 ng/mL (50 nmol/L) is usually called deficient, and 20 to 29 ng/mL (50 to 74 nmol/L) is insufficient on this site's scale. Low levels are very common and easy to recheck.
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Typical adult range
Your lab may print a slightly different range. Use the one on your report when there is one.
| Test | Adults |
|---|---|
| Vitamin D (25-OH) | Deficient: under 20 ng/mL Insufficient: 20–30 ng/mL Sufficient: 30–100 ng/mL Too high: 100 or more ng/mL |
| Calcium | 8.6–10.3 mg/dL2.15–2.57 mmol/L |
What the vitamin D test measures
The usual test measures 25-hydroxy vitamin D, written as 25-OH vitamin D or 25(OH)D. It reflects the vitamin D you get from sunlight on your skin, food and supplements over the past few weeks. Vitamin D helps your gut absorb calcium and phosphorus, which keeps bones and muscles healthy. US and Indian labs often report in ng/mL, while the UK and Europe use nmol/L. Multiply ng/mL by 2.5 to convert. Experts differ on the ideal level: some, including the NHS, treat 20 ng/mL (50 nmol/L) as enough for most people, while others aim for 30 ng/mL.
Who is more likely to have low vitamin D
Low vitamin D is very common worldwide, including in sunny countries like India and Pakistan, where many people spend most of the day indoors or cover most of their skin. Darker skin needs more sun to make the same amount of vitamin D. Levels are often lowest at the end of winter. A blood test is the only reliable way to know your level, because symptoms are vague and many people have none.
- Little time outdoors, or clothing that covers most of the skin
- Darker skin, older age or excess body weight
- Diets low in oily fish, eggs and fortified foods
- Conditions that affect absorption, such as coeliac disease or bowel surgery
- Kidney or liver disease and some medicines, such as some seizure drugs
Symptoms and why calcium is checked
Many people with low vitamin D feel completely well. Others notice bone pain, aching muscles, muscle weakness or tiredness, though these have many other causes. Over time, a severe lack can soften bones, called osteomalacia in adults and rickets in children, and can add to bone thinning. Doctors often check calcium (normal 8.6 to 10.3 mg/dL, or about 2.15 to 2.58 mmol/L) at the same time. A low calcium with low vitamin D needs closer attention. A high calcium with low vitamin D can point to a parathyroid problem.
What usually happens next
If your level is low, your doctor may suggest more safe sun exposure, more vitamin D foods and a vitamin D supplement, with the dose based on your level, age and health. The level is usually rechecked after about three months. Very high doses taken without supervision can push vitamin D above 100 ng/mL (250 nmol/L) and raise calcium to unsafe levels, so follow your doctor's plan rather than guessing a dose. If calcium, phosphorus or kidney results are also abnormal, your doctor may order a parathyroid hormone (PTH) test.
When to get help the same day
Get same-day care if your calcium is below 6.5 mg/dL (1.6 mmol/L) or above 13 mg/dL (3.25 mmol/L), or your vitamin D is above 150 ng/mL (375 nmol/L). Call your local emergency number for muscle spasms or cramps that will not stop, tingling around the mouth, a seizure, severe confusion, or vomiting with extreme thirst.
Questions to ask your doctor
- Is my vitamin D low enough to need treatment, or just more sun and food?
- If I need a supplement, what dose and for how long?
- Is my calcium normal, and do I need a PTH test?
- Should my bone health be checked?
- When should I repeat the test?
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Frequently asked questions
What is a normal vitamin D level?
On this site's scale, 30 to 100 ng/mL (75 to 250 nmol/L) is sufficient, 20 to 29 ng/mL is insufficient and under 20 ng/mL is deficient. Some health bodies, including the NHS, consider 20 ng/mL (50 nmol/L) enough for bone health in most people, so ask your doctor which target applies to you.
Can low vitamin D make you tired?
Some people with low vitamin D report tiredness or aching muscles, but tiredness has many causes, such as anaemia, thyroid problems, poor sleep and low mood. If you feel very tired, it is worth checking these too, rather than assuming vitamin D is the only reason.
How long does it take to raise vitamin D?
With a supplement suggested by your doctor, levels usually rise over 6 to 12 weeks. That is why the test is normally repeated after about three months, not sooner. How fast it rises depends on the dose, your starting level and your body weight.
Is sunlight enough to fix low vitamin D?
Short periods of midday sun on bare arms and legs help many people, but it depends on where you live, the season, your skin colour and how much skin is covered. Avoid sunburn. If your level is very low, your doctor will usually suggest a supplement as well.
Sources
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