The National Diet and Nutrition Survey, covering 2019 to 2023, found that 18% of UK adults aged 19 to 64 had vitamin D levels below the threshold used to define deficiency. Seasonal results from the survey combine data from 2016 to 2023 and put the figure at 31% for blood samples taken between January and March. At that time of year, the skin makes little or no vitamin D from sunlight.
Vitamin D deficiency symptoms are often vague, and many people with low levels notice nothing at all. Signs of vitamin D deficiency, such as aching bones or muscle weakness, overlap with many other health issues, so a blood test is needed to confirm low vitamin D. Low levels are common, and once they have been identified, a doctor can advise on how to manage them. For anyone in a higher-risk group, low vitamin D symptoms like these can be a useful prompt to speak to a doctor.
What Does Vitamin D Do in the Body?
Vitamin D is involved in how the body absorbs and uses calcium and phosphorus from food. The bones, teeth, and muscles all need these minerals, which is why vitamin D is most closely linked with bone and muscle health. Calcium intake and physical activity also influence how the bones are maintained through adult life.
Vitamin D3 (cholecalciferol) is made in the skin when it is exposed to ultraviolet B (UVB) light from the sun, and is also found in some animal foods. Vitamin D2 (ergocalciferol) is found in some mushrooms, particularly those exposed to ultraviolet light, and in some fortified foods. Both forms are fat-soluble, and the body cannot use either straight away, as the liver and then the kidneys first convert vitamin D into its active form.
In the UK, health claims about nutrients can only use wording that has been reviewed and approved by regulators. These approved statements, known as authorised claims, are held on a public list called the GB Nutrition and Health Claims Register. It is the wording of the claim that is authorised, not the nutrient itself. The authorised claims for vitamin D state that it:
- contributes to normal absorption/utilisation of calcium and phosphorus
- contributes to normal blood calcium levels
- contributes to the maintenance of normal bones
- contributes to the maintenance of normal muscle function
- contributes to the maintenance of normal teeth
- contributes to the normal function of the immune system
Vitamin D Deficiency Symptoms and Signs to Watch For
Symptoms of low vitamin D tend to develop gradually and are shared with many other conditions. They are easy to put down to a busy period or a long winter, so low levels can go unnoticed for some time.
When vitamin D levels stay low for a long period, the body may absorb less calcium from food. To keep blood calcium within its normal range, the body may then draw more calcium from the bones, which over time may affect the bones themselves. Low vitamin D levels are also associated with muscle aches and weakness.
Commonly reported symptoms of a lack of vitamin D in adults include:
- tiredness or a general sense of feeling unwell
- aching bones, particularly in the lower back, hips, pelvis, and legs
- muscle weakness, aches, or cramps
- difficulty with everyday movements, such as climbing stairs or getting up from a low chair
Feeling persistently tired can be wearing, and because tiredness has many possible causes, it is worth raising with a doctor before assuming vitamin D is involved.
Signs That Should Be Checked by a Doctor
Bone pain or muscle weakness that makes walking difficult should be assessed by a doctor, particularly if it comes with a change in the way someone walks or a bone breaks after a minor fall. Long-term, severe vitamin D deficiency is associated with osteomalacia, a softening of the bones in adults, and with rickets in children, which can affect growth and cause bowed legs. Where severe vitamin D deficiency symptoms are present, identifying the underlying cause should come before any nutritional support.
What Causes Low Vitamin D?
In the UK, the sun is not strong enough for the skin to make vitamin D between October and early March, so levels tend to fall through autumn and winter. Sunlight is the main source of vitamin D for most people, and even in summer, spending most of the day indoors or covering most of the skin outdoors limits how much the skin can make.
People with darker skin, for example those of African, African-Caribbean, or South Asian background, may make less vitamin D from the same amount of sunlight. The skin’s ability to make vitamin D may also decline with age.
Only a small number of foods contain vitamin D, so diet alone may not make up for limited sunlight. Some digestive conditions can affect how vitamin D is absorbed, and because the liver and kidneys convert it into its active form, conditions affecting either organ can play a part. Certain medicines can also affect vitamin D levels, so for anyone with a long-term health condition or taking regular medication, a doctor is the right person to ask about vitamin D status.
Who Is More Likely to Have Low Levels?
The groups more likely to have low vitamin D levels include:
- people who are rarely outdoors, such as those who are frail or housebound
- people living in care homes
- people who usually cover most of their skin when outdoors
- people with darker skin
- older adults
- pregnant and breastfeeding women
- babies and children under five
How Is Low Vitamin D Confirmed?
A vitamin D test measures 25-hydroxyvitamin D, the main form of vitamin D that circulates in the blood and the one used to assess vitamin D status. Doctors do not routinely test everyone, although a test may be arranged for someone with bone or muscle symptoms, or with a health condition that makes low levels more likely.
Results are given in nanomoles per litre (nmol/L). In the UK, a result below 25 nmol/L is generally classed as deficient, and a result between 25 and 50 nmol/L may be insufficient for some people. Guidelines do not all use the same thresholds, and laboratories may report ranges slightly differently, so results are best interpreted by the doctor who requested the test. Home finger-prick vitamin D tests are also available, and any result from one can be discussed with a doctor or pharmacist.
A confirmed deficiency is managed by a doctor. Treatment sometimes involves a higher-dose course for a set period, followed by a daily maintenance amount and, in some cases, a follow-up blood test.
How to Support Healthy Vitamin D Levels
Vitamin D has specific authorised roles on the GB Register, including contributing to the maintenance of normal bones and to the maintenance of normal muscle function. Where a deficiency is diagnosed, the doctor will advise on treatment, which is a separate matter from taking everyday food supplements. No supplement replaces a varied and balanced diet and a healthy lifestyle.
Spend Time Outdoors Between Spring and Early Autumn
Between late March or early April and the end of September, most people can make all the vitamin D they need from sunlight on their skin and a balanced diet. Regular time outdoors with some skin uncovered, such as a walk at lunchtime or time spent in the garden, can contribute to this. Vitamin D cannot build up to harmful levels from sunlight, though the skin should still be covered or protected during longer periods in the sun to reduce the risk of burning and skin damage.
Include Foods That Contain Vitamin D
Food is another way to get vitamin D. Foods that contain it include:
- oily fish, such as salmon, sardines, trout, herring, and mackerel
- red meat
- egg yolks
- fortified foods, such as some fat spreads and breakfast cereals
- liver, although liver should be avoided during pregnancy because of its high vitamin A content
Several of these can be included in everyday meals, such as eggs at breakfast or oily fish for an evening meal. In the UK, cows’ milk is generally not fortified with vitamin D as it is in some other countries, so it is not a reliable source.
Follow NHS Guidance on Vitamin D Supplements
The NHS advises that everyone, including pregnant and breastfeeding women, should consider taking a vitamin D supplement containing 10 micrograms (mcg) each day during autumn and winter. During these months, it is difficult to get enough vitamin D from food alone. Supplement labels may show the amount in international units (IU) instead, and 10mcg is equal to 400 IU.
For people who are rarely outdoors, live in a care home, or usually cover most of their skin when outside, the NHS advises taking a daily 10mcg supplement all year round. People with darker skin are also advised to consider taking one throughout the year. Babies and young children have separate NHS guidance, which parents can check with a health visitor or pharmacist.
Taking too much vitamin D over a long period can cause calcium to build up in the body, a condition called hypercalcaemia, which can weaken the bones and damage the kidneys and heart. The NHS advises adults, including pregnant and breastfeeding women, not to take more than 100mcg (4,000 IU) a day. Anyone whose doctor has recommended a different amount should follow that advice.
Vitamin D3 in supplements is typically derived from lanolin, which comes from sheep’s wool, while vegan vitamin D3 comes from lichen. The label shows the amount of vitamin D per daily dose, which is useful to check when choosing either a multivitamin or a standalone vitamin D product. The form of a nutrient can influence how it is absorbed and used by the body, and some supplements use forms chosen for their bioavailability. Anyone with an existing health condition, or who takes regular medication, should speak to a doctor or pharmacist before starting a new supplement.
Supporting Vitamin D Levels Through Autumn and Winter
Day-to-day, time outdoors in the warmer months and foods that contain vitamin D can both help maintain normal levels, and the NHS advises most people to consider a daily 10mcg supplement through autumn and winter.
Vitamin D contributes to the maintenance of normal bones, and calcium is needed for the maintenance of normal bones. Regular physical activity plays a part in supporting bone health as well. Vitamin D also contributes to the normal function of the immune system, and vitamin C and zinc hold the same authorised claim.
Drawing on more than 30 years of Good Health Naturally’s experience, our nutrition team is available to discuss general nutritional support, including where vitamin D fits alongside diet and daily routine.
Food supplements should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. Anyone concerned about their vitamin D levels, or experiencing persistent symptoms, should speak to a doctor.
Frequently Asked Questions
How Long Does It Take to Raise Vitamin D Levels?
This depends on how low levels were to begin with and whether a deficiency has been diagnosed. If a doctor has confirmed a deficiency, treatment usually runs for a set period, and levels may be re-checked with a follow-up blood test. How long treatment continues, and when to re-test, is best guided by the doctor managing it.
Does Low Vitamin D Make You Tired?
Tiredness is one of the symptoms some people with low vitamin D report, but it has many possible causes, including poor sleep, stress, diet, and other health conditions. A doctor can look at the possible reasons for persistent tiredness and arrange a blood test if needed. Vitamin D does not hold an authorised claim relating to tiredness. Magnesium contributes to the reduction of tiredness and fatigue, and vitamin C holds the same authorised claim.
How Much Vitamin D Should I Take?
NHS guidance is 10mcg (400 IU) a day for adults and children aged one and over. Most adults are advised to consider this amount during autumn and winter. People who are rarely outdoors, live in a care home, or usually cover most of their skin outdoors are advised to take it all year round, as are children aged one to four. People with darker skin are advised to consider it throughout the year.
Can You Get Enough Vitamin D From Sunlight in the UK?
Between late March or early April and the end of September, most people can make the vitamin D they need from sunlight on their skin. Between October and early March, the sun in the UK is not strong enough for the skin to make vitamin D. People who spend little time outdoors, cover most of their skin, or have darker skin may not make enough even in the summer months.
Can You Take Too Much Vitamin D?
Yes, from supplements, although not from sunlight. Taking too much over a long period can lead to hypercalcaemia, where calcium builds up in the body. The NHS advises adults not to take more than 100mcg (4,000 IU) a day unless a doctor has recommended otherwise.
