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Vitamin D Deficiency Symptoms, Causes and Testing
Updated: 9 hours ago
Vitamin D deficiency is much more common than most people realise. Almost one in five adults aged 19–64 in the UK have low vitamin D levels. During winter, that figure rises to almost one in three.
It's not hard to understand why. Unlike most vitamins, our bodies produce vitamin D when sunlight reaches our skin. But between October and March, the British sun simply isn't strong enough.
The problem is that vitamin D deficiency isn't always obvious. You might feel tired all the time, notice weakness in your muscles, or experience persistent bone pain. Or you might have no symptoms at all.
In this guide we will cover:
What is Vitamin D Deficiency?
Vitamin D deficiency occurs when your body doesn't have enough vitamin D to maintain healthy bones and muscles. Its main role is to help the intestines absorb calcium and phosphate, two minerals that keep our bones strong.
Without enough vitamin D, calcium absorption falls. Over time, this can weaken the bones and affect normal muscle function.
In addition to its role in bones, it plays a role in regulating the immune system, alongside other nutrients like vitamin C.
Vitamin D is often associated with sunlight. When our skin is exposed to sun rays, it produces vitamin D. This is very different to how we get other vitamins. That said, we can still get vitamin D from food and supplements.
What Causes Vitamin D Deficiency?
The most common cause of vitamin D deficiency is not getting enough sunlight. Between October and early March, a combination of overcast days and weak sun means our bodies can't produce adequate vitamin D.
Instead, our bodies rely on the vitamin D we’ve stored during summer, alongside what we can get from our diet.
The chart below shows how strong the midday sun is across the UK throughout the year:
Sunlight isn’t the sole factor, however.
Other common causes include:
Spending too much time indoors. If you work in an office all day, you might rarely see the sun, even during summer.
Darker skin. Melanin (the dark pigment your skin produces) reduces how much vitamin D the skin produces in response to sunlight.
Ageing. As we get older, our skin becomes less efficient at producing vitamin D.
Poor diet. Very few foods naturally contain substantial amounts of vitamin D.
Digestive conditions. Conditions like Crohn's disease and coeliac disease can prevent the body from absorbing vitamin D properly.
Medications. Certain anticonvulsants and glucocorticoids (prednisolone) can interfere with vitamin D metabolism.
People with obesity, kidney disease, or liver disease are also at greater risk. Even someone who eats a relatively healthy diet can become deficient if they're not getting enough sunlight.
Is Vitamin D Deficiency Linked to Seasonal Affective Disorder and Depression?
Vitamin D deficiency and seasonal affective disorder (SAD) share something in common: they're both more prevalent during winter.
Researchers have found an association between low vitamin D levels and depression. Vitamin D is involved in several processes within the brain, including pathways related to mood regulation.
However, that doesn't necessarily mean vitamin D deficiency causes depression. The evidence remains mixed, and taking supplements hasn't consistently been shown to improve depressive symptoms.
What Are the Signs of Low Vitamin D?
One of the problems with vitamin D deficiency is that the symptoms are fairly general. Feeling tired, having aching muscles, or struggling with exercise could indicate a deficiency. But the same symptoms occur with numerous other conditions.
In fact, mild vitamin D deficiency often causes no noticeable symptoms.
What Are 14 Signs of Vitamin D Deficiency In Adults?
Common symptoms and possible manifestations of more severe deficiency include:
Area | Sign | Details |
Energy | Persistent fatigue | Feeling exhausted despite adequate rest |
Muscles | Muscle weakness | Particularly around the hips and thighs |
Muscles | Muscle aches | Persistent discomfort without an obvious injury |
Muscles | Muscle cramps | Sometimes caused by low calcium levels |
Bones | Lower back pain | Aching associated with poorly mineralised bones |
Bones | Hip pain | Discomfort around the pelvis and upper legs |
Bones | Rib pain | Tenderness or aching around the chest |
Bones | Leg pain | Particularly around the thighs |
Bones | Bone fractures | Weakened bones may break more easily |
Movement | Difficulty climbing stairs | Due to weakened leg muscles |
Movement | Difficulty standing up | Especially from a low chair |
Movement | Changes in walking | Including a waddling gait |
Movement | Frequent falls | Resulting from muscle weakness |
Nerves | Tingling sensations | Possible if severe deficiency causes low calcium |
Several of these symptoms overlap. The most characteristic signs of severe vitamin D deficiency are bone pain and weakness in the muscles around the hips and thighs.
If you're experiencing persistent symptoms, it's worth speaking to a healthcare professional rather than assuming vitamin D is responsible.
Recognise a few of these? Our Fatigue Blood Test checks vitamin D, iron, B12 and thyroid problems all in one test.
Health Risks of Long-Term Vitamin D Deficiency
Initially, vitamin D deficiency is mild. Most people won’t notice any immediate problems. It’s only after prolonged deficiency that people develop osteomalacia, a condition where the bones become soft and more vulnerable to fractures.
Osteomalacia can cause aching bones, muscle weakness, and difficulty walking.
In children, vitamin D deficiency can cause rickets. Because their bones are still growing, they can become deformed, sometimes leading to bowed legs. Rickets used to be extremely rare. However, children spending prolonged periods inside has significantly increased the incidence.
How Does Vitamin D Deficiency Affect Bone Health, Muscles, and the Immune System?
Vitamin D deficiency means the body no longer absorbs enough calcium and phosphate. Without these building block minerals, the bones become weaker and more fragile.
Muscles are also not as strong, especially around the hips and thighs. You may find climbing stairs, standing, or simply maintaining your balance more difficult.
Lastly, there’s the immune system. Persistently low levels of vitamin D can open the door to some infections. It’s one potential reason why colds spike during the cooler months. However, there is limited evidence that taking extra vitamin D prevents illness.
How to Fix Vitamin D Deficiency
For most people, preventing vitamin D deficiency is relatively simple.
The NHS recommends that everyone in the UK considers taking a 10 microgram (400 IU) vitamin D supplement daily during autumn and winter.
If you spend very little time outdoors or have darker skin, it's recommended that you consider taking a supplement throughout the year.
During summer, spending time outdoors can help maintain vitamin D levels. However, you should still protect your skin from sunburn. There's no need to deliberately sunbathe or use tanning beds.
If you're already severely deficient, your doctor may prescribe a higher dose for several weeks. Don't simply take large doses yourself. Excess vitamin D can cause calcium to build up in your blood, potentially damaging your kidneys.
Best Food Sources for Vitamin D Deficiency
Unfortunately, vitamin D isn't particularly abundant in food. That's part of the reason deficiency is so common.
The best dietary sources include:
Oily fish, particularly salmon, mackerel, and sardines
Egg yolks
Red meat and liver
Fortified breakfast cereals
Fortified spreads and plant-based milks
UV-exposed mushrooms
Oily fish contains some of the highest natural concentrations. But even with a balanced diet, getting enough vitamin D during winter can be difficult.
How Is Vitamin D Deficiency Diagnosed by Doctors?
The only reliable way to confirm vitamin D deficiency is through a blood test.
Doctors measure 25-hydroxyvitamin D, the main circulating form of vitamin D in your blood. In the UK, concentrations below 25 nmol/L are considered low enough to increase the risk of poor bone and muscle health.
Results usually fall into one of four ranges. Enter your own result below to see what it means.
Not everyone needs testing. Doctors usually recommend it when someone has symptoms of significant deficiency, suspected bone disease, or an underlying condition affecting vitamin D levels.
They may also check calcium, phosphate, and kidney function to see whether the deficiency has affected other parts of the body.
Vitamin D Tests at Health Klinix
If you're feeling constantly tired or experiencing unexplained muscle weakness, checking vitamin D alone might not give you the full picture.
For example, iron deficiency anaemia and an underactive thyroid can cause similar symptoms. That's why a broader blood test can sometimes be more useful.
At Health Klinix, vitamin D testing is included in our: Fatigue Blood Test, Well Man Check and Well Woman Check
Our fatigue blood test checks vitamin D alongside iron, B12, folate, thyroid function, blood glucose, and other markers. Think of it as a general health check with a particular focus on identifying possible causes of exhaustion.
Book your blood test with Health Klinix and find out whether a deficiency could be contributing to your symptoms.
Your Questions Answered
Who is most at risk of vitamin D deficiency?
People who rarely go outdoors, have darker skin, or are older are particularly vulnerable. That’s because the skin plays an important role in producing Vitamin D utilising UV sunlight. People with obesity, digestive disorders, or certain kidney and liver conditions also have an increased risk. If you have a medical condition like Crohn’s or coeliac disease you may fail to absorb sufficient vitamin D from your gut and can therefore become deficient. Once you absorb the vitamin D, the kidneys then convert it into an active form of vitamin D that the body can use. This step can be blocked if you have chronic kidney disease.
How do you feel when your vitamin D is low?
You might feel tired, have aching bones, or notice muscle weakness. You can also have difficulty in performing simple tasks like getting out of a chair or climbing stairs. Vitamin D also plays an important role in your immune function, so any vitamin D deficiency can make you potentially more susceptible to infection including tuberculosis. However, mild deficiency often produces no symptoms. If you're constantly tired, it's worth considering other causes, including anaemia and thyroid problems.
What drains vitamin D from your body?
Nothing necessarily drains vitamin D. Low levels usually result from inadequate production from your skin using sunlight or insufficient dietary intake of vitamin D rich foods such as oily fish, eggs, butter and fortified cereal. Even if your intake is good, if your small intestine can’t absorb it or your kidneys (due to disease) are unable to convert the vitamin D into a useful form, you may still become vitamin D deficient. Certain medications such anti-epileptics, steroids, and even excessive laxatives can also contribute.
Can low vitamin D affect sleep?
Some research has found a relationship between low vitamin D and poor sleep quality. However, it's unclear whether deficiency directly causes sleep problems. Taking vitamin D isn't an established treatment for insomnia.
How to raise vitamin D quickly?
Supplements are the most reliable method. If you have mild vitamin D deficiency, you can buy vitamin D at a dose of about 400 i.u. per day. If you're severely deficient and/or have medical conditions, you’ll need much higher doses but only your doctor can prescribe high-dose vitamin D. It can also take several weeks or months for levels to recover.
Which food is highest in vitamin D?
Oily fish is among the richest natural sources of vitamin D. Salmon, herring, sardines, and mackerel all contain vitamin D. Fortified margarines, breakfast cereals and plant-based milks (Soya and oat milk) can also contribute to your daily intake. Eggs, wild mushrooms, red meat and liver are also rich sources of vitamin D.
References
Written by:
Dr Joseph Nightingale, MBBS, MSc
Approved by:
Consultant in Infectious Diseases and Travel Medicine
MBBS, MRCP(UK), DTM&H, MRCGP, DCH, DRCOG, DFFP
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