Roughly 1 in 6 people in the UK have insufficient vitamin D levels, making it the most common vitamin deficiency in the country — and most people with it don't have any obvious symptoms at all. When symptoms do appear, they're often subtle and easy to put down to something else, from tiredness to low mood to bone and muscle aches.
Vitamin D is a fat-soluble vitamin that's unique among nutrients: it's the only one your body can make itself, produced in the skin following exposure to sunlight. It plays a central role in calcium and phosphate absorption, bone health, muscle function, and immune regulation. In this article, we'll cover the signs and symptoms of a vitamin D deficiency, who's most at risk, what healthy levels look like, and what you can do about it.
What are the signs and symptoms of vitamin D deficiency?
Most people with low vitamin D don't notice any symptoms, which is part of why it's so common and often goes undiagnosed. When symptoms do appear, they can include:
- Fatigue and persistent tiredness
- Bone pain, particularly in the back
- Muscle weakness, aches, or cramps
- Impaired or slow wound healing
- Increased susceptibility to infections
- Low mood
- Hair loss
- Bone weakness or softness, with an increased risk of fractures
In children, inadequate vitamin D can additionally lead to rickets (softened, misshapen bones), delayed growth, and dental problems. Because these symptoms overlap with many other conditions, a blood test is the only reliable way to confirm a deficiency rather than diagnosing it from symptoms alone.
Low vitamin D has also been linked in research to a wider range of conditions, including dental issues such as periodontitis, cardiovascular problems, autoimmune conditions (including type 1 diabetes, inflammatory bowel disease, and psoriasis), and pregnancy complications such as pre-eclampsia. These associations don't necessarily mean low vitamin D causes these conditions, but they're part of why maintaining healthy levels matters beyond bone health alone.
Who is at risk of a vitamin D deficiency?
Some groups are considerably more likely to have low vitamin D:
- Older adults, as ageing skin becomes less efficient at producing vitamin D from sunlight, and the body becomes less able to convert it into its active form
- People with darker skin, as higher melanin content absorbs more UV rays, reducing vitamin D production
- Anyone with a low-fat diet or fat malabsorption issues, since vitamin D is fat-soluble and needs dietary fat to be absorbed properly
- People who are obese, as excess body fat can bind vitamin D and reduce how much circulates in the blood
- Anyone with limited sun exposure, including people who are housebound, cover most of their skin, or live somewhere with limited sunlight for much of the year — which includes most of the UK from October to March
How do you know if your vitamin D levels are healthy?
A vitamin D blood test, measuring 25-hydroxyvitamin D, is the only way to know your actual level rather than guessing from symptoms. This can be done via your GP or with an at-home vitamin D test. For a full breakdown of what counts as deficient, insufficient, and optimal, see our guide to what are healthy vitamin D levels.
What foods contain vitamin D?
Sunlight is the main source of vitamin D for most people, but dietary sources can help top up your levels, particularly over autumn and winter:
- Oily fish (salmon, mackerel, sardines, herring)
- Cod liver oil
- Egg yolks
- Mushrooms (particularly those grown under UV light)
- Beef liver
- Fortified foods, including some milk, plant-based milks, breakfast cereals, and fat spreads
If you follow a vegetarian or vegan diet, dietary sources are more limited — mushrooms are one of the only naturally occurring plant sources of vitamin D, so fortified foods and supplements become more important. See our guide to the best vitamin D foods for vegans for more detail.
What are the benefits of maintaining healthy vitamin D levels?
Bone and muscle health
Vitamin D is essential for absorbing calcium and phosphate, the key building blocks of bone. Research has also found a link between the active form of vitamin D and muscle mass and strength, particularly relevant for maintaining mobility as we age.
Immune function
Vitamin D plays a role in regulating the immune system, including how immune cells called B cells and T cells respond to and communicate about threats like infections. Adequate levels are thought to support the body's ability to defend against illness.
How much vitamin D do you need, and how do you get it safely?
The Scientific Advisory Committee on Nutrition (SACN) recommends that everyone in the UK over the age of 5 take a daily vitamin D supplement of 10 micrograms (400 IU), particularly during autumn and winter when sunlight exposure is limited. For more detail on boosting your levels day to day, see our guide to improving your vitamin D levels.
For sun exposure, around 10–15 minutes of midday sun on your face and forearms during spring and summer (up to double for darker skin tones) is generally enough to support your levels through the year, even on overcast days. Sunscreen significantly reduces vitamin D production, so it's best applied after this initial exposure window, and always balance this against safe sun exposure to avoid burning.
It is possible to take too much vitamin D from high-dose supplements, though not from sunlight or food. If you're considering a higher-dose supplement, it's worth speaking to a nutritionist or GP first, particularly if you take other medications. High-dose supplements have also been associated with digestive side effects in some people — see does vitamin D cause constipation for more detail.
FAQ
How common is vitamin D deficiency in the UK?
Around 1 in 6 people in the UK have insufficient vitamin D levels, making it the most common vitamin deficiency in the country, particularly during the winter months.
Can you have vitamin D deficiency with no symptoms?
Yes — most people with low vitamin D don't experience noticeable symptoms, which is why testing is the only reliable way to confirm a deficiency.
How long does it take to correct a vitamin D deficiency?
This depends on how low your levels are and the dose used to correct them, and is best guided by a healthcare professional following a blood test — confirmed deficiencies are often treated with a supervised high-dose course over several weeks. See our full guide on vitamin D deficiency treatment: how long does it take to feel better for more detail.
Can you get enough vitamin D from food alone?
It's difficult. Dietary sources are limited, and most people rely on a combination of sunlight exposure and, particularly in autumn and winter, a daily supplement.
If you think you might be low in vitamin D, our at-home Vitamin D test can confirm your levels without waiting for a GP appointment.
