Vitamin D Deficiency: The Cause of Unexplained "Bone Ache"

Condition 14 October, 2026

Understanding vitamin D deficiency and its impact

What is vitamin D and how does your body get it?

Vitamin D is a chemical your body needs for strong bones and muscles. It comes in 2 forms: vitamin D2 and vitamin D3.

Both vitamin D2 and vitamin D3 are prohormones ie substances that are converted into hormones. Your body activates vitamin D2 and vitamin D3 by converting them into a hormone that keeps your bones and muscles healthy.

There are 3 main ways you can get vitamin D and prevent vitamin D deficiency:

Being exposed to the sun – this triggers a chemical reaction in your skin that allows your body to make vitamin D from cholesterol in your skin
Eating foods naturally rich in vitamin D (eg beef liver, egg yolks, and oily fish such as salmon and tuna) or vitamin D-fortified foods (eg fortified cow’s milk, breakfast cereals, orange juice and oat milk)
Taking a daily supplement of vitamin D (eg a daily vitamin D tablet or a teaspoon of cod liver oil)

What is vitamin D deficiency and why does it matter?

If you have vitamin D deficiency, your bone health and muscles may be affected.

Vitamin D helps your body absorb calcium from food in your gut. Calcium is needed to keep your bones strong. Calcium is also needed to prevent your muscles from cramping.

Who is most vulnerable to developing vitamin D deficiency in the UK?

Certain medical conditions are risk factors for vitamin D deficiency. This includes gastrointestinal disorders that reduce your ability to absorb calcium from your gut (eg inflammatory bowel disease and coeliac disease).

If you have epilepsy and take anti-epileptic medication, you are also at higher risk. This is because certain anti-epileptic medications affect how vitamin D is used by the body.

Other medical conditions that increase your risk of vitamin D deficiency are liver disease and kidney disease. This is because vitamin D is activated in the liver and kidneys.

If you have limited sun exposure, for example, if you are house-bound due to reduced mobility, you are more likely to develop a vitamin D deficiency. If you have had bariatric surgery for weight loss, your risk of a vitamin D deficiency is higher too.

Additionally, people with darker skin are more vulnerable to vitamin D deficiency than people with lighter skin. This is because darker skin reduces the skin’s ability to trigger the process that will produce vitamin D.

Bone pain causes linked to vitamin D deficiency

Why does vitamin D deficiency cause bone ache and discomfort?

Vitamin D allows your body to absorb calcium and phosphorus from your gut. Both calcium and phosphorus are used by your body to create strong bones.

As your bone tissue gets old, cells called osteoclasts break it down. Then, other bone-building cells called osteoblasts use calcium and phosphorus to create hard crystals that form the building blocks of your bones.

If you have low vitamin D levels, the bone-building cells can’t produce enough new bone tissue to replace worn-out bone tissue. This causes your bone density to decrease, which makes your bones soft.

As your bones weaken, they become less able to carry your weight. These soft bones then develop tiny cracks called micro-fractures, which cause bone ache and discomfort.

What is osteomalacia and how is it connected to low vitamin D?

If you have very low levels of vitamin D, you can develop osteomalacia. Osteomalacia refers to weakened, soft bones. It can cause bone pain, joint pain, muscle pain and muscle cramps.

Osteomalacia happens when vitamin D levels become so low that your body can’t absorb enough calcium and phosphorus from your food. Your body converts vitamin D into a hormone called calcitriol, which acts on cells in your gut to allow calcium and phosphorus to pass into your body.

Recognising common and unexpected symptoms

If you have mild to moderately low vitamin D levels (vitamin D insufficiency), it’s likely that you won’t have any symptoms. However, if your vitamin D levels are significantly lower, ie you have vitamin D deficiency, you may notice symptoms.

Common signs of severe vitamin D deficiency in adults include:

A tingling or numb sensation in your hands and/or feet
Bone pain, ache or discomfort
Fatigue and joint pain
Muscle weakness and muscle pain
Muscle spasms and muscle cramps

You may also experience anxiety, depression and low mood due to the effects of vitamin D on the brain.

How is vitamin D deficiency diagnosed medically?

Vitamin D deficiency is diagnosed with a blood test to check for levels of 25 hydroxyvitamin D in your blood serum (the liquid part of your blood that doesn’t contain any cells).

Measuring 25 hydroxyvitamin D is, therefore, a good way to check your vitamin D levels. For a healthy body, optimal serum concentrations of vitamin D are 50-100 nmol/L. This is called vitamin D sufficiency.

If your vitamin D levels are in the range of 25-50 nmol/L, you have vitamin D insufficiency. If your vitamin D levels are less than 25 nmol/L, you have vitamin D deficiency.

Can you have too much vitamin D?

Yes, you can have too much vitamin D. This can happen if you take high doses of vitamin D supplements.

Vitamin D is a fat soluble vitamin, so any unused vitamin D is stored in fat and not quickly removed from your body. This can allow vitamin D levels to build up.

When vitamin D levels become too high, you develop vitamin D toxicity. Its symptoms are usually caused by excess vitamin D increasing calcium levels in your blood.

Check your vitamin D levels

For healthy bones and muscles, you need to make sure your body has just the right amount of vitamin D. If you’re concerned about bone aches, joint pain or muscle cramps, your vitamin D levels may be too low.

Find out your vitamin D levels with a simple at-home blood test when you book our Essential Health MOT.