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Vitamin D pills forming a D shape on a wooden background

Vitamin D deficiency: how to identify and treat

01 Sep 2022 • 3 min read

Vitamin D absorbs calcium, supporting bone and teeth health and cell growth. As we are spending more time in our homes, a daily dose of vitamin D has never been more important to help you and your family stay well1.

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What is Vitamin D?

Vitamin D, aka “the sunshine vitamin”, is one of the most important vitamins for our bodies. Even better, we can make it ourselves by getting out and enjoying the sun!

This helpful vitamin allows us to absorb calcium and phosphate from the foods we eat to keep our teeth, bones, and muscles healthy.

However, if we don’t get enough sunlight or eat enough vitamin D-rich foods, it is all too easy to develop a deficiency in vitamin D.

We’ve written this definitive guide to help you spot vitamin D deficiency symptoms and find out if you need a little more of the sunshine vitamin in your life.

Holland & Barrett's guide to vitamin D deficiency

Why is Vitamin D important for your health?

You might know about the link between vitamin D deficiency and rickets (which is called osteomalacia in adults).

Rickets is a condition which affects the bones. It causes them to become soft and weak, often leading to deformities and fractures.

In fact, vitamin D3 was first recognised when scientists were trying to work out why cod liver oil was so effective in dealing with rickets. So, can a lack of vitamin D cause rickets?

In short, yes - vitamin D deficiency is one of the main causes of rickets, a condition that affects children’s bones.

But our bones are not the only parts of our bodies that rely on enough vitamin D:

  • Lack of vitamin D has also been linked to muscle weakness and fatigue.
  • Studies have also shown that vitamin D deficiency can contribute to an impaired immune system
  • Vitamin D receptors in our brains help brain cells receive and understand chemical signals – a lack of vitamin D is likely to affect the way our brain communicates.

How much vitamin D per day do I need?

The NHS recommends that everyone over the age of 5 takes a 10μg (400IU) vitamin D supplement every day between October and March.³

This applies to adults, children, the elderly, and those who are pregnant or breastfeeding. However, taking more than 100 micrograms (4,000 IU) a day could be harmful to your health.

Because we get most of our vitamin D from the sun, our intake falls in the autumn and winter.

Babies under 1 year need a slightly smaller amount - 8.5 to 10μg per day. If your baby drinks formula milk, they don’t need a vitamin D supplement as their formula will already contain enough.

If they’re breastfed, it’s recommended you give them a vitamin D supplement for babies.

Handpicked content: 12 of the best vitamin D supplements

How much vitamin D per day do I need?

The NHS recommends around 10 micrograms a day.

It is recommended to take supplements containing 10 micrograms of vitamin D during autumn and winter, and throughout the year for those who are not often outdoors.

Taking more than 100 micrograms (4,000 IU) a day could be harmful to your health. This applies to adults, children, the elderly, and those who are pregnant or breastfeeding.6

Causes of vitamin D deficiency

Since we get up to 90% of our vitamin D from the sun, the main cause of vitamin D deficiency is not getting enough sunlight.⁴

This means everyone’s at a higher risk during the autumn and winter months. However, certain groups of people may receive less vitamin D (or require more than the recommended dose) all year round…

Groups of people who are more likely to be deficient in vitamin D

  1. Vegans

Vegans can have low levels of vitamin D, since most natural food sources are animal-based.

Pay extra attention to your diet and eat fortified foods (cereals, plant milk, and orange juice) and take a high-quality vitamin D supplement.

  1. Those not exposed to sunlight

Limited sunlight exposure can put you at risk. If you:

  • Are housebound for any reason
  • Live in a grey climate
  • Cover your skin for work, lifestyle, or religious reasons

This could mean that your skin might not get enough sunlight to make the vitamin D your body needs.

Remember, your skin needs to be exposed to the sun without sun protection or clothing covering it to absorb vitamin D. However, wearing an SPF of at least 30 every day is still important.

Instead, it’s recommended that you look to increase your dietary vitamin D or consider a supplement.

  1. People with darker skin

The pigment in your skin can reduce your ability to make vitamin D, even if you get plenty of sunlight. Older adults with dark skin are particularly at risk.

A carefully planned diet rich in vitamin D, a supplement, or both is recommended.

  1. Those over 50

Once you’re over 50, you lose some of your natural ability to produce vitamin D from sun exposure – making you one of the most at-risk groups.

Your kidneys also become less efficient at converting the vitamin, making it important to stay active and spend plenty of time outside in your 50s, 60s, and beyond.

Read more about the importance of vitamin D when you’re older here.

What are the most common symptoms of vitamin D deficiency?

Symptoms of low vitamin D vary from person to person. But, if you think you’re at risk, look out for these symptoms:

  1. Low mood

Our bodies need vitamin D to effectively make serotonin (the “happy hormone”) in the brain. If you often feel low or irritable, it could be a sign that you are deficient in vitamin D.

  1. Weak muscles

Vitamin D deficiency is strongly linked to muscle weakness in ageing adults.⁵ Your legs can feel heavy and it can feel difficult to stand up and climb stairs - all of which make falls and fractures an increased risk.

  1. Getting sick often

 If you seem to catch every cold going around, it may be down to low levels of vitamin D.

This is because vitamin D is essential for keeping your immune system strong and healthy.

  1. Weight gain

If your appetite has gone through the roof or you are gaining weight, vitamin D may be playing a role.

Research has revealed that low levels of vitamin D are associated with being overweight and obese, whereas higher levels of vitamin D are associated with reductions in body fat.

This may be because vitamin D helps to control a hormone in the body called leptin, which helps to inhibit hunger and reduce fat storage. If the body is low in vitamin D and struggles to produce healthy levels of leptin, this could contribute to overeating and weight gain.⁵
 Please note: People considered overweight or obese need more vitamin D than a person with a healthy weight. This also applies if you have high muscle mass.

  1. Fatigue

People who are tired all the time, especially older adults, may not suspect a vitamin D deficiency could be draining their energy. Increasing vitamin D levels have been seen to improve signs of fatigue.⁶

  1. Achy bones and joints

Vitamin D deficiency affects bone health, which could result in a throbbing or achy feeling in your bones. This is often most noticeable in the knees and back.

Those who do not have enough of this important vitamin may be at more risk of fractures.

  1. Head sweats

A common, early sign of vitamin D deficiency is a sweaty scalp (this is one reason newborn babies are monitored for head sweats).

Can a lack of vitamin D cause depression?

Ever noticed how much happier you feel when you have been outside in the sunshine?

Vitamin D3 is produced by our bodies when we get enough of the sun’s UVB rays on our skin. But that is not the only link between sunlight, Vitamin D, and mood. Research into Vitamin D and emotional health has shown that people with low levels of Vitamin D are up to 11 times more prone to depression than people with normal levels of the vitamin.⁷

Studies in this complex area are few and far between. But more work is being done and we can expect some interesting research to be published in future.

What do I do if I think I have low vitamin D?

If you think your fatigue and achy muscles could mean that you’re lacking vitamin D, the only accurate way to diagnose a deficiency is with a vitamin D test.

Your doctor can arrange a simple blood test, or you can do it at home using a vitamin D home test. These rely on a finger-prick blood sample.

Measuring the concentration of 25-hydroxyvitamin D in your blood is the best way to identify a vitamin D deficiency.⁹

Anywhere between 20 ng/mL and 50 ng/mL is a healthy vitamin D level. If your test shows less than 12 ng/mL, it suggests you have a vitamin D deficiency.¹

Vitamin D deficiency treatments

The first thing to do if you find out you’re deficient in any nutrient is to speak with your GP.

Normally, the best way for your body to make vitamin D is through exposure to the sun. However, sunlight is often not enough to reverse an already-existing deficiency.

It’s the same with diet: increasing the vitamin D you eat will help, but it is difficult to get enough vitamin D from food alone.

The best vitamin D deficiency treatment is to take a daily supplement of 10μg all year round.

That said, it’s also worth increasing your sunlight exposure (safely) and dietary vitamin D intake where you can:

How to increase vitamin D in your diet

Here are some of the best foods you can eat if you’re low in vitamin D:

  • Salmon
  • Mackerel
  • Herring
  • Sardines
  • Red meat
  • Eggs
  • Offal (e.g. animal stomach, tripe, brains, heart, liver, tongue, and kidneys)
  • Wild mushrooms or mushrooms grown under UV light

You can also choose foods fortified with vitamin D, such as:

  • Dairy
  • Plant milks
  • Breakfast cereals
  • Fruit juices
  • Meat alternatives
  • Fat spreads

Get out in the sunshine more

Quick mythbuster: your body can’t make vitamin D with sunlight that shines through a window. You’ll need to be outside to reap the benefits.⁵

Skin colour and skin exposure play a big part in how much vitamin D your skin will absorb. People with darker skin will need to spend longer in the sun to produce the same amount of vitamin D as somebody with lighter skin.

You also need to make sure you don’t burn in the sun, so make sure you always have sun protection and sunglasses handy.

Please seek shade if you plan to be out in the sun for a long time – the longer you stay in the sun unprotected, the greater your risk of skin cancer is.

The final say

If you think you’re at risk of low vitamin D, speak to your GP. They’ll be able to arrange a blood test and, with their support, you can start taking a quality vitamin D3 supplement.

There’s a supplement out there for everyone - from the elderly and newborn babies to people following a vegan diet.

You’ll find one that’s right for you - just browse our range of vitamin D supplements to find tablets, capsules, liquids, gummies, sprays, and more.

Last updated: 1 September 2022

The advice in this article is for information only and should not replace medical care. Please check with your GP or healthcare professional before trying any supplements, treatments or remedies. Food supplements must not be used as a substitute for a varied and balanced diet and a healthy lifestyle.

Before taking any supplements or minerals, it’s best to make sure you’re getting all the nutrients through your diet first.

Food supplements must not be used as a substitute for a varied and balanced diet and a healthy lifestyle.


Donia Hilal



Joined Holland & Barrett: January 2018

Bsc in Nutrition, Registered Associate Nutritionist and Certification in Pre and Post Natal Nutrition

Donia started her career as a freelance nutritionist, later she joined Nestle as their Market Nutritionist to help support their healthier product range, before joining the team at Holland & Barrett in January 2018.

Donia has over 6 years experience as a Nutritionist and also works with clients on a one to one basis to support their goals which include weight loss, prenatal and postnatal nutrition and children’s health.

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