How do I know if I’m low on vitamin D?

Not reliably. Low vitamin D can cause bone pain and weak muscles, but these can have other causes too. A blood test is the only way to know your level.

You don’t need a test before taking a standard vitamin D supplement. The NHS advises everyone to consider taking 10 micrograms a day in autumn and winter, and some people all year. A test can help if you have symptoms, are in a higher risk group or want to check that what you’re doing is working.

Vitamin D helps control the amount of calcium and phosphate in your body. These are needed to keep your bones, teeth and muscles healthy. A lack of vitamin D can lead to soft, weak bones, called rickets in children and osteomalacia in adults.

Researchers have studied links between low vitamin D and other conditions, such as heart disease, cancer and infections. But most of this evidence comes from studies that can’t show cause and effect, and trials of vitamin D supplements have given mixed results. That’s why UK advice on vitamin D is based on bone and muscle health.

Low vitamin D can lead to rickets in children and osteomalacia in adults. The NHS lists these symptoms:

• pain in your back, shoulders, ribs, pelvis or legs
• weak muscles, making it hard to climb stairs or get up from a chair
• tingling, cramping or twitching in your muscles
• changes in the way you walk
• breaking bones more often

In children, the main sign of rickets is bowed legs. Children can also have swollen, painful wrists, weak muscles and poor growth.

These problems can have other causes, so see a doctor if you have any of them.

Tiredness, hair loss, low mood, anxiety, weight gain and frequent colds are often blamed on low vitamin D, but UK health bodies don’t list them as symptoms.

• Weight gain is the wrong way round: people with a high body mass index (BMI) are more likely to have low vitamin D.
• Studies that link low vitamin D with low mood can’t show that one causes the other.
• Daily low dose vitamin D may slightly lower the risk of respiratory infections, such as colds, in children and young people aged 1 to 15. UK experts saw no effect from the age of 16.

If you feel tired all the time, see a doctor. Tiredness has many possible causes, including an underactive thyroid. Read more in “How to know when to get a thyroid test”

Fairly common, especially in winter. The latest National Diet and Nutrition Survey, covering 2019 to 2023, found these shares had low vitamin D (below 25 nmol/L) over the year:

• 10% of children aged 4 to 10
• 23% of children aged 11 to 18
• 18% of adults aged 19 to 64
• 12% of adults aged 65 and over

Levels are lowest from January to March. At that time of year, between 21% and 38% of people aged 11 and over had low vitamin D, depending on their age and sex. From July to September, it was no more than 10%.

You’re more likely to be low on vitamin D if you:

• aren’t often outdoors, for example because you’re frail, housebound or live in a care home
• usually cover most of your skin when you’re outdoors, or wear sunscreen most of the time
• have dark skin, for example if you have an African, African-Caribbean or south Asian background
• are pregnant or breastfeeding
• are aged 65 or over
• have a high BMI
• have a condition that affects how your body takes in or uses vitamin D, such as Crohn’s disease, coeliac disease, or severe liver or kidney disease
• take certain medicines, such as some medicines for epilepsy

Babies and young children also need extra vitamin D, which is why the NHS advises a daily supplement for them all year.

From about late March or early April to the end of September, most people can make all the vitamin D they need from sunlight. The NHS recommends spending a short time in the sun each day, and your skin can still make vitamin D on cloudy days, although it takes longer. If you have dark skin, you may need more time in the sun to make the same amount.

Between October and early March, we don’t make enough vitamin D from sunlight in the UK. You can’t get too much vitamin D from the sun, but cover up or protect your skin if you’re out for long periods, to lower the risk of skin damage and skin cancer.

Vitamin D is found in only a few foods:

• oily fish, such as salmon, sardines, trout, herring and mackerel
• red meat
• egg yolks
• liver, although you should avoid it if you’re pregnant
• fortified foods, such as some fat spreads and breakfast cereals

In the UK, cows’ milk isn’t usually fortified, so it isn’t a good source. It’s hard to get enough vitamin D from food alone, which is why supplements are recommended.

The NHS advises:

• Everyone, including pregnant and breastfeeding women, should consider taking 10 micrograms a day in autumn and winter.
• Adults and children over 4 should take 10 micrograms a day all year if they’re not often outdoors, live in a care home or usually cover most of their skin outdoors. If you have dark skin, consider taking it all year too.
• Children aged 1 to 4 should have 10 micrograms a day all year.
• Babies under 1 should have 8.5 to 10 micrograms a day all year if they’re breastfed, or have less than 500ml of infant formula a day, as formula already contains vitamin D.

10 micrograms is the same as 400 IU, and it’s enough for most people. The NHS says adults and children aged 11 to 17 shouldn’t take more than 100 micrograms (4,000 IU) a day, and younger children have lower limits. Taking too much over a long time can make calcium build up in your body, which can weaken your bones and damage your kidneys and heart. If a doctor has recommended a different dose, follow their advice.

UK guidance says you don’t normally need a vitamin D test. A test can be worth having if:

• you have symptoms such as bone pain or muscle weakness
• you’re at higher risk, for example because you rarely go outdoors or have a condition that affects how you absorb vitamin D
• you take vitamin D and want to check your level

The test measures a form of vitamin D called 25-hydroxyvitamin D in your blood. UK experts use 25 nmol/L as the cut-off: below this, the risk of poor bone and muscle health goes up.

If your level is low, a doctor can advise you on the right dose. Don’t take high doses without medical advice. If you test with us, a Better2Know doctor can discuss your result and ways to improve your level.

Better2Know offers:

• Vitamin D: a blood test at one of our clinics, with results in 1 day. A nurse can also come to a place of your choice to take your sample.
• Vitamin D home test kit: take a small blood sample at home and post it back to our lab, with results in 1 day.

Read more in “How to take a blood sample for a home test”

Not sure which test you need? Our Patient Care Team is available 24/7 on 020 7099 0955.

Can you take too much vitamin D?

Yes, from supplements. The NHS says adults shouldn’t take more than 100 micrograms (4,000 IU) a day, and children under 11 have lower limits. You can’t get too much vitamin D from sunlight.

Should I take vitamin D all year round?

It depends. The NHS advises everyone to consider it in autumn and winter, and all year if you’re rarely outdoors, cover most of your skin outside or have dark skin. Young children usually need it all year too.

Can low vitamin D be treated?

Yes. The NHS says rickets and osteomalacia are treated with vitamin D and calcium supplements. If a test shows your level is low, a doctor can advise you on how much to take.

Low vitamin D is common in the UK, especially in winter, but it’s hard to spot from symptoms alone. The main signs are bone pain and muscle weakness. A daily 10 microgram supplement in autumn and winter is enough for most people, and a blood test can tell you your level if you have symptoms or a higher risk.

Book a Vitamin D test at a clinic near you or order a home test kit. Our Patient Care Team is available 24/7 on 020 7099 0955.

Not in the UK? Choose your country from the selector at the top of the page for local tests and prices.

This article originally appeared on 7 April 2023 and was last updated on 1 October 2026.

This article is general information and not a substitute for personal medical advice.

Sources

1. NHS, Vitamin D, reviewed 3 August 2020. https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/
2. NHS, Rickets and osteomalacia, reviewed 9 July 2025. https://www.nhs.uk/conditions/rickets-and-osteomalacia/
3. NHS, Sunscreen and sun safety, reviewed 24 March 2026. https://www.nhs.uk/live-well/seasonal-health/sunscreen-and-sun-safety/
4. NHS, Osteoporosis: prevention, reviewed 13 October 2022. https://www.nhs.uk/conditions/osteoporosis/prevention/
5. NHS, Underactive thyroid (hypothyroidism), reviewed 28 April 2025. https://www.nhs.uk/conditions/underactive-thyroid-hypothyroidism/
6. Office for Health Improvement and Disparities, National Diet and Nutrition Survey 2019 to 2023: report, 11 June 2025. https://www.gov.uk/government/statistics/national-diet-and-nutrition-survey-2019-to-2023/national-diet-and-nutrition-survey-2019-to-2023-report
7. Scientific Advisory Committee on Nutrition, Vitamin D and health, July 2016. https://www.gov.uk/government/publications/sacn-vitamin-d-and-health-report
8. Scientific Advisory Committee on Nutrition, Update of rapid review: vitamin D and acute respiratory tract infections, December 2020. https://www.gov.uk/government/publications/sacn-rapid-review-vitamin-d-and-acute-respiratory-tract-infections
9. NICE, Vitamin D: supplement use in specific population groups (PH56), 2014, updated December 2020. https://www.nice.org.uk/guidance/ph56/chapter/Recommendations
10. Royal Osteoporosis Society, Vitamin D, reviewed 1 July 2025. https://theros.org.uk/information-and-support/food-and-supplements/vitamin-d/
11. British Dietetic Association, Vitamin D: food fact sheet, November 2024. https://www.bda.uk.com/resource/vitamin-d.html