Vitamin D deficiency: Causes, symptoms and prevention

20th September, 2018 • 17 min read

According to

research published in the Journal of Pharmacology and Pharmacotherapeutics
, 50% of the global population doesn’t get enough vitamin D.

A survey conducted in 2011
has also shown that around 46% of the US population is at risk of developing a vitamin D deficiency.

According to the BMJ
, Vitamin D deficiency is actually the most common nutritional deficiency worldwide**. Despite this, it is also the most underdiagnosed medical condition in both children and adults.

One of the reasons a vitamin D deficiency is often unrecognised is because the symptoms in mild disease can be extremely subtle, ranging from tiredness to muscle weakness or bone pain.

However, vitamin D is needed to keep your bones strong and regulate several hormonal processes in your body. As a result, long term or severe vitamin D deficiency can cause or increase the risk of:

Studies have also linked vitamin D deficiency with an increased risk of high blood pressure, diabetes, some forms of cancer such as bowel cancer, depression, dementia and respiratory infections.

Unfortunately, a tendency to spend more time indoors is putting more and more people at risk of developing a vitamin D deficiency every year.

A study published in Endocrine Connections
shows a strong upward trend in the number of people being diagnosed with a vitamin D deficiency between 1993 and 2013. This includes people who:

  • Spend a lot of time working indoors
  • Don’t eat much dairy produce
  • Don’t eat enough oily fish

People living in countries with low levels of natural light may also be at increased risk of developing a vitamin D deficiency.

If you’re concerned that you might be suffering from a vitamin D deficiency, try not to worry too much. The condition can be serious, but it is also treatable.

Understanding the causes, and adapting your lifestyle to increase your vitamin D levels, may be enough to remedy the problem. There are also several different types of Vitamin D supplement that you can take if you struggle to get enough sun, or if you are unable to eat foods that are rich in vitamin D.

Here, you can read about the causes, symptoms and treatment of vitamin D deficiency, as well as learning about the groups who are most at risk of developing the condition.

Common causes of vitamin D deficiency

Vitamin D is a fat soluble vitamin that helps your body to absorb calcium, phosphate and magnesium from your food. These 3 essential minerals are needed for a number of internal processes, from bone density to the way that certain hormones are regulated.

Unlike most vitamins, vitamin D is not found in many foods. Low levels are found in oily fish like mackerel or salmon, and dairy produce, beef liver or egg yolks can also provide trace amounts of vitamin D. It is however difficult to get all of your vitamin D from your diet alone.

We can make our own Vitamin D through a process known as photolyzation, where UVB radiation is used to transform cholesterol into vitamin D2, which is the most accessible form of vitamin D.

This process does require exposure to bright or direct sunlight though, which means that it can be difficult to get enough vitamin D if:

  • You work indoors for most of the day
  • You live in the northern hemisphere, where light levels tend to be lower
  • You suffer from a medical condition that prevents you from getting outside as often

According to

research published by Harvard University
, you’re most likely to develop a vitamin D deficiency if your lifestyle prevents you from getting enough sun, and you don’t eat many of the foods that contain vitamin D.

Everybody living above or below a latitude of 35 degrees is at some risk of developing a vitamin D deficiency too - particularly during the winter months.


International Osteoporosis Foundation have a map
of the countries most commonly associated with vitamin D deficiency, and
articles published by Harvard Health
have some local maps of the American states most likely to be affected too.

Groups at risk of developing vitamin D deficiency

Because most of our vitamin D comes from exposure to sunlight, some people have an increased risk of developing a vitamin D deficiency. This includes people who can’t get outside for medical reasons, people who work night shifts, elderly people, pregnant women and vegans.

If you fall into one of these groups, it is important to keep track of your vitamin D levels. The symptoms of vitamin D deficiency can be subtle, which means that people with a high risk of developing a vitamin D deficiency will need to take extra precautions.

This may include using a service like

to track your vitamin D levels if you live in the UK, or booking regular appointments with your doctor. You could also consider taking a regular vitamin D supplement.

Guidelines released by the Scientific Advisory Committee
state that people with an increased risk of developing a vitamin D deficiency should take between 600-1000 IU of supplemental vitamin D per-day.

People with darker skin

Melanin - the pigment responsible for tanning of skin exposed to sunlight - acts as a natural sunscreen by blocking out UVB radiation and protecting us from skin cancer. Unfortunately, melanin also impedes the process of synthesising your own vitamin D, and people with high levels of melanin do tend to produce less vitamin D than people with light or fair skin.

If your skin contains a lot of melanin, you will need to spend more time in the sun, or eat more dietary sources of vitamin D to ensure that you don’t develop a vitamin D deficiency.

People with fair skin

Studies published in the BMJ
show that sunblock with a high SPF rating can reduce vitamin D creation by up to 95%. This means that people who have to use a high-factor sunblock to protect their skin are at more risk of developing a vitamin D deficiency.

People who cover up when they go outside

If you wear clothes that cover most of your skin for religious reasons, or prefer modest clothing that keeps your arms and legs out of the sun, you will be reducing your exposure to UVB radiation.

This may prevent your body from making enough vitamin D and increase your risk of becoming deficient.

To compensate, it is important to consider increasing the amount of time spent outdoors. You can also prevent or correct a vitamin D deficiency by adding more sources of vitamin D to your diet, or by taking a regular supplement.

If you do cover up a lot of your skin when you go outdoors, you may also want to track and monitor your vitamin D levels.

People who work night shifts

An article published by the Vitamin D Council
shows that people who regularly work night shifts are more likely to develop one or more of the conditions associated with chronic vitamin D deficiency as a direct result of their reduced exposure to UVB radiation.

If your job involves lots of night-shifts and you have to sleep a lot during the day, it is important that you take extra steps to prevent or correct vitamin D deficiency. You can do this by taking a regular supplement or by adding more sources of vitamin D to your diet. Talk to your doctor about scheduling regular tests to check if you have a vitamin D deficiency.

People who are housebound

Since most of our vitamin D comes from exposure to natural light, people who are housebound due to a medical condition, or struggle to get outside due to a disability, are at increased risk of developing a vitamin D deficiency.

If you can’t get the recommended 30-60 minutes of direct sunlight every day, it is important you track your vitamin D levels. You should also talk to your doctor about making sure that you get enough vitamin D.

Increasing dietary sources of vitamin D, or taking a vitamin D supplement, can help to correct a deficiency. Following the advice found in the

treatment section of this article
may also help to prevent a deficiency from developing.

Elderly people

Research published in Clinical Interventions in Aging
shows that age can slow down the chemical processes that create vitamin D. Elderly people may also find it harder to spend time outdoors, particularly if mobility is an issue.

Unfortunately, old age does tend to make the symptoms of vitamin D deficiency worse, and elderly people are at increased risk of developing conditions like

. This means that it’s important to keep on top of your vitamin D levels if you’re over 60 years old.

Young children

Young children need a lot of vitamin D to thrive. Their bones are growing quickly, and a steady supply of calcium and phosphate is needed to ensure that they don’t develop a condition like



studies published in the Archives of Pediatric and Adolescent Medicine
show a resurgence in vitamin D deficiency - most likely as a result of the tendency to spend more time indoors.


Due to the fact that the main dietary sources of vitamin D are dairy produce, beef, liver, fish, and egg yolks, many vegans struggle to get enough vitamin D from their diets.

This isn’t a problem if you have adequate access to sunlight, but vegans living in an area with low year-round light levels are at a high risk of developing vitamin D deficiency.

People suffering from a malabsorption problem

A study published in Inflammation Research
points to a tentative link between vitamin D deficiency and malabsorption problems like
irritable bowel syndrome
Crohn's disease

People suffering from these conditions may find it hard to absorb vitamin D from dietary sources, and they may also be at increased risk of suffering from the symptoms due to their inability to absorb sufficient calcium, phosphate and magnesium too.

Pregnant women

The link between weight gain and vitamin D deficiency isn’t fully understood, but some studies have

pointed to an increased requirement for vitamin D during pregnancy

Pregnant women are at particularly high risk if they are pregnant during the winter months, have dark skin, or develop gestational diabetes, which interferes with the body’s ability to create vitamin D.

If you are pregnant, you should check your vitamin D levels throughout your pregnancy. It is also advisable to eat plenty of vitamin D-rich foods, and spend 30-60 minutes outside every day if you can.

Symptoms of Vitamin D Deficiency

Vitamin D is involved in the regulation of hormones responsible for growth and development. It’s also needed to help your body absorb micronutrients like calcium and phosphate, which means it plays an important role in most of the biochemical processes that take place in your body.

As a result, the symptoms of a vitamin D deficiency can be far-ranging, subtle and difficult to diagnose. When your vitamin D drops below the level needed to maintain your health you may notice:

  • General muscle pain and weakness
  • Frequent muscle cramps
  • Joint pain
  • Bone pain
  • Tiredness
  • Poor concentration

They will be able to diagnose the condition easily by taking a blood test, and can also recommend an appropriate treatment.

You can also test your own vitamin D levels using a home testing service. These services are a recent innovation, designed to help you monitor your health from the comfort of your own home.

Most home testing services will provide you with the resources needed for a finger-prick blood test, which you can then mail to a laboratory capable of testing the amount of vitamin D in your blood.

Vitamin D deficiency can cause

in children, as well as osteomalacia in adults.

There is also some evidence linking Vitamin D deficiency to conditions like:

  • Heart disease
  • High blood pressure
  • Cancers such as bowel cancer
  • Diabetes
  • Depression
  • Dementia
  • Some autoimmune diseases

So it is important to diagnose a possible deficiency as soon as you possibly can.

Treating Vitamin D Deficiency

Once diagnosed, a vitamin D deficiency is relatively easy to fix. Treatment options are designed to increase the amount of vitamin D in your system, and include:

Getting more direct sunlight

Increasing your exposure to sunlight will help your body to make more of its own Vitamin D. This is the most effective way of treating a vitamin D deficiency, but it can be difficult if you have trouble getting outside, live in an area with low levels of natural light, or struggle to find time to spend in the sun.

You don’t have to stay outside all day though: The exact amount of sunlight needed to make enough vitamin D varies by person, but 15-30 minutes of bright sunlight per-day should be enough for most people.

Getting enough sun will be impossible for some people in the winter months. If you live above a latitude of 35 degrees north, or below a latitude of 35 degrees south, you will need to take advantage of the summer sun by spending plenty of time outdoors between March and October. This will help you to refill your body’s stores of Vitamin D.

If you plan on spending more time outside, make sure that you take adequate precautions. Exposure to too much UVB radiation carries an increased risk of skin cancer, and a chance of sunburn.

Try to leave your arms, lower legs, hands and feet exposed, but cover up your torso and make sure that your head is covered too. Making sure that you never spend more than 30-40 minutes in direct sunlight can help to protect you too.

Sunscreen will slow the rate at which you make vitamin D, but wearing at least an SPF 15 sunblock can provide additional protection, and this is essential for children and babies.

Eating more vitamin-D-rich foods

Adding more oily fish, egg yolk or dairy produce to your diet is a simple and straightforward way of providing your body with more vitamin D.

For people living in the northern hemisphere, and particularly those areas with low levels of winter sunshine, adding more dietary vitamin D is also a fantastic way of keeping your levels topped up in the Oct-Feb period.

It’s important to remember that most foods contain very little vitamin D though. Even the dietary sources recommended by most doctors contain between 30-10% of your recommended daily intake (800 IU/day).

This means that you have to eat a good variety of vitamin-D-rich foods to ensure that you’re providing your body with enough vitamin D.

The best dietary sources of vitamin D are listed below:

Choosing a vitamin D supplement

Taking a vitamin D supplement can also help to boost the levels of vitamin D in your blood. These supplements are normally supplied as tablets or capsules, and need to be taken at least once per day.

If you struggle to get enough sunlight, and can’t eat enough of the foods mentioned earlier in this article, a vitamin D supplement may be the simplest way of addressing a deficiency.

When it comes to choosing a supplement, you may notice that there are two types: Vitamin D2 supplements, and Vitamin D3 supplements.

Both types function by providing the ingredients needed to help your body create more vitamin D, but D2 comes from plant sources, while D3 is often derived from animals. D2 will provide adequate levels of vitamin D, but

studies published in the American Journal of Clinical Nutrition
have shown that a D3 is much more effective in boosting or maintaining vitamin D levels compared with D2 supplements.

If you are not vegan or vegetarian, it is recommended that you take a vitamin D3 supplement. If you would prefer not consume a supplement that could be derived from animal sources, your safest bet is to opt for D2.

Can I take too much Vitamin D?

Getting the correct dosage when taking a vitamin D supplement is very important. You may have seen for yourself that vitamin D supplements come in a range of different strengths, from 400 IU (or international units) up to 10,000 IU. It can be tempting to assume that higher strength tablets are better, but too much vitamin D has been associated with the build up of too much calcium in the blood, which can cause:

  • Vomiting
  • Weakness
  • Frequent urination

Research published by the American Journal of Clinical nutrition
also shows that chronic hypercalcaemia (a high calcium level in the blood) has been linked to the development of kidney stones.

Advice published by the Royal National Orthopaedic Hospital
states that 400 IU is sufficient for most adults, while children between one month and eighteen years of age should aim for 600-1000 IU per day.

It is best to take regular doses of vitamin D too, so try to pick out a tablet that provides the recommended dosage. This will allow you to take one per day, without putting you at risk of taking too much vitamin D.

Preventing vitamin D deficiency

If you fall into one of the

high-risk groups
listed earlier in this article, you may want to consider taking extra steps to make sure that you get enough vitamin D - even if you’re not currently deficient.

This could include taking a regular supplement, or making sure that you add plenty of vitamin D-rich foods to your diet.

It is important to check your vitamin D levels regularly too. They will fluctuate based on the amount of sunlight that you receive, and some people can develop a vitamin D deficiency without developing symptoms.

If you’re in the UK, you can use a service like

to track the amount of vitamin D in your blood. Alternatively, your doctor will be able to check your vitamin D levels at regular intervals.

If you find that you have been suffering from a vitamin D deficiency, it is also important to remember that your body won’t have been getting enough calcium either. Vitamin D is needed to absorb calcium from your food, and a long term deficiency can make your bones weak or fragile.

If you are trying to prevent this, you may also be interested in reading more about the things you can do to strengthen your bones. Eating more calcium-rich foods may also help.

If you are over 65, you may need to take extra steps to protect your bones.

Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.