Vitamin D plays a vital role in keeping bones, muscles and the immune system healthy, yet deficiency remains common, particularly during the UK's darker months when sunlight is limited.

Many of the symptoms, such as tiredness, muscle aches and low mood, can easily be mistaken for stress, ageing or other health conditions. As a result, people may not realise that low vitamin D levels could be contributing to how they feel.

Understanding the warning signs and knowing when to seek medical advice can help prevent longer-term complications.

What Is Vitamin D and Why Is It Important?

Vitamin D helps the body absorb calcium and phosphate, two minerals essential for maintaining strong bones, healthy teeth and normal muscle function.

Unlike most vitamins, vitamin D is produced naturally when the skin is exposed to sunlight. It can also be obtained from certain foods and supplements.

Dr Kathryn Basford, an online doctor at Asda Online Doctor, explained why maintaining healthy vitamin D levels is so important.

'Vitamin D is needed for the body to regulate phosphate and calcium; these are nutrients that we need to keep our bones, muscles, and teeth healthy and strong,' she said.

Without enough vitamin D, the body struggles to absorb calcium effectively, increasing the risk of bone disorders over time.

How Common Is Vitamin D Deficiency?

Vitamin D deficiency is relatively common in the UK, particularly during autumn and winter when sunlight exposure is reduced.

According to the NHS, everyone should consider taking a daily vitamin D supplement during the autumn and winter months because it can be difficult to produce enough through sunlight alone.

Some people remain at higher risk throughout the year, including those who:

  • Spend little time outdoors
  • Regularly cover most of their skin outdoors
  • Have darker skin tones
  • Live in care homes
  • Are older adults
  • Have certain medical conditions affecting nutrient absorption

What Are the Symptoms of Vitamin D Deficiency?

The symptoms of low vitamin D often develop gradually and may be subtle at first.

'The most common symptoms of low vitamin D are tiredness, aches and pains, muscle weakness, and bone pain,' Dr Basford said.

Because these symptoms overlap with many other conditions, vitamin D deficiency cannot usually be diagnosed based on symptoms alone.

Persistent tiredness

Feeling constantly tired despite getting enough sleep may be one of the earliest signs.

Vitamin D deficiency has been linked to reduced energy levels and poorer sleep quality in some people.

Muscle weakness

Weak muscles can make everyday activities more difficult, particularly climbing stairs, standing up from a chair or carrying shopping.

Some people notice reduced physical performance or slower recovery after exercise.

Bone and joint pain

Vitamin D deficiency may cause aching bones or tenderness, particularly in the lower back, hips, pelvis or legs.

Long-term deficiency can weaken bones and increase fracture risk.

Frequent illness

Emerging research suggests low vitamin D levels may influence immune function.

Dr Basford noted that inadequate vitamin D has been linked to 'how often you get unwell,' although maintaining healthy vitamin D levels is only one part of supporting the immune system.

Can Low Vitamin D Affect Your Mood?

Low Mood / Sad / Vitamin D Deficiency
Low vitamin D has been linked to symptoms of depression and anxiety, but it is rarely the only cause of low mood. Magnific

Possibly.

Several studies have found an association between vitamin D deficiency and symptoms of depression or anxiety, although the relationship is complex and vitamin D is unlikely to be the sole cause.

'Low vitamin D can sometimes be associated with increased symptoms of depression and anxiety,' Dr Basford said.

'A lack of vitamin D can disrupt the brain's ability to produce serotonin, a chemical which is crucial for mood regulation.'

She added that muscle pain, fatigue and disrupted sleep caused by deficiency may also contribute to low mood.

Anyone experiencing persistent depression or anxiety should seek medical advice rather than assuming vitamin D is the only cause.

What Happens if Vitamin D Deficiency Is Left Untreated?

Over time, prolonged vitamin D deficiency can have serious consequences.

Children may develop rickets, a condition that affects normal bone development.

Adults are at risk of osteomalacia, which causes bones to become soft and painful.

Dr Basford also highlighted research linking low vitamin D levels with an increased risk of certain chronic conditions, including diabetes and heart disease. However, while these associations exist, scientists are still investigating whether vitamin D deficiency directly contributes to these conditions.

How Is Vitamin D Deficiency Diagnosed?

Symptoms alone are not enough to confirm vitamin D deficiency.

'The only way to know for sure if you have low vitamin D levels is with a blood test,' Dr Basford said.

If deficiency is confirmed, your GP may recommend or prescribe vitamin D supplements depending on how low your levels are and your overall health.

How Can You Increase Your Vitamin D Levels?

Spend time outdoors

Sunlight remains the body's main source of vitamin D.

'In the UK, you can usually get enough vitamin D from late March to September, as long as you spend time outside each day,' Dr Basford explained.

During autumn and winter, however, sunlight is often too weak for adequate vitamin D production.

Eat foods containing vitamin D

Although relatively few foods naturally contain vitamin D, useful sources include:

  • Oily fish such as salmon and mackerel
  • Egg yolks
  • Liver
  • Red meat
  • Fortified breakfast cereals
  • Fortified spreads

A balanced diet can help support vitamin D intake, although food alone may not always provide enough.

Consider supplements

The NHS recommends that most people consider taking a daily vitamin D supplement between October and March.

Some higher-risk groups may benefit from supplementation all year round following medical advice.

However, supplements are not suitable for everyone.

'You should not take vitamin D tablets if you have a condition that makes it hard to absorb nutrients (malabsorption), high levels of vitamin D, or high levels of calcium,' Dr Basford said.

Anyone unsure whether supplements are appropriate should consult their GP or pharmacist.

Common Myths About Vitamin D

Myth: You can tell if you're deficient by your symptoms

Not necessarily.

Many symptoms are non-specific, and some people with low vitamin D have no symptoms at all. A blood test is needed for diagnosis.

Myth: More vitamin D is always better

Taking excessive vitamin D supplements can lead to dangerously high calcium levels and should be avoided unless advised by a healthcare professional.

Myth: Sunlight alone is enough all year

In the UK, sunlight during autumn and winter is generally insufficient to produce enough vitamin D, which is why supplements are recommended for many people.

When Should You See Your GP?

Arrange a medical assessment if you experience:

  • Persistent tiredness without an obvious cause
  • Muscle weakness
  • Ongoing bone pain
  • Recurrent fractures
  • Symptoms that do not improve despite lifestyle changes

Your GP can decide whether a blood test is appropriate and recommend treatment if needed.

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