What is Vitamin D deficiency? Symptoms, causes and prevention

What is vitamin D?

Despite its name, vitamin D is not a vitamin but a prohormone (precursor of a hormone) made in our skin, and a nutrient found in certain foods. Its key role is to help regulate the amount of phosphate and calcium in the body, which is needed to keep bones, teeth and muscles healthy. Additionally, there is some evidence that vitamin D is needed to support immune, brain, cardiovascular, and nervous system health, as well as normal lung function.

Why is vitamin D important?

Vitamin D’s role in promoting optimal calcium absorption is essential to maintain good musculoskeletal health in both adults and children. In fact, it protects children from various conditions including rickets, and adults from osteomalacia – which are both conditions causing soft, weak, and sometimes painful bones. Such disorders can lead to osteoporosis, which is the loss of bone density, and can in turn result in fractures.

Research also suggests that vitamin D might be beneficial in the treatment or prevention of certain conditions, such as cardiovascular disease, cancer, infections and neurological conditions – though this is more controversial.

How much vitamin D do I need?

The Department of Health and Social Care (DHSC) recommends that adults in the UK need 10 micrograms (400iu) of vitamin D a day.

During the autumn and winter, we need to get vitamin D from our diet as the sunlight is not strong enough for the body to produce a sufficient amount of vitamin D. However, as it is difficult for people to get enough vitamin D from food alone, the DHSC recommends that everyone aged one and above should consider taking a daily supplement containing 10 micrograms of vitamin D during the autumn and winter.

Most people can get all the vitamin D they need through sunlight on their skin and from a balanced diet between late March/early April to the end of September, so you may choose not to take a vitamin D supplement during these months. However, the DHSC recommends taking a daily supplement of 10 micrograms of vitamin D throughout the year if you are at risk of vitamin D deficiency due to having a dark skin, not going outdoors regularly, and/or covering up most of your skin when outside.

Can you have too much vitamin D?

Vitamin D surplus occurs when there is an excess of vitamin D in the body. This usually stems from taking too many supplements.

It is essential to note that taking vitamin D supplements may not be safe if you suffer from certain pre-existing medical conditions, so always consult your GP if you are in doubt. If your doctor has recommended you take a different amount of vitamin D, you should follow their advice.

An excess of vitamin D is a rare but potentially serious condition. It can damage the kidneys, heart and bones and occurs when you have excessive amounts of vitamin D in your body. This can only be caused by large amounts of vitamin D being taken in supplement form, as the body is able to regulate the amount of vitamin D gained through sun exposure, and foods do not contain enough vitamin D to cause a surplus.

What is vitamin D deficiency?

Vitamin D deficiency can be caused by a number of medical and more individual reasons pertaining to age, lifestyle and diet. Therefore, some of us are more inclined to developing a deficiency and may need to take certain necessary steps to increase their intake.

What are the causes of vitamin D deficiency?

Medical causes

Vitamin D deficiency can be caused by certain medical conditions, such as:

Vitamin D levels can also be negatively affected by certain medications, including laxatives, steroids, seizure-control drugs, cholesterol-lowering drugs, tuberculosis drugs, and weight-loss drugs.

Individual causes

In addition to medical causes, certain personal factors can also contribute to vitamin D deficiency.

  • Age: as we age, our skin’s ability to produce vitamin D lessens.
  • Sunlight exposure: not getting enough sunlight can lead to vitamin D deficiency. People at greater risk of having this lack of sun exposure include those with reduced mobility (such as frail people and those living in care homes), people who always wear clothes that cover up most of their skin when outdoors, and people who are located in countries where the sunlight can be limited, such as Nordic countries. Consistently wearing high factor sunscreen can also reduce vitamin D levels.
  • Skin colour: the pigment melanin, which is more prevalent in darker skin, reduces the skin’s ability to make vitamin D in response to sunlight exposure.
  • Diet: certain diets such as strict vegan diets may cause a deficiency, as most vitamin D gained from food comes from animals.
  • BMI (Body Mass Index): A BMI greater than 30 is commonly associated with lower vitamin D levels. This is due to fat cells keeping vitamin D isolated, which means it is not released for the body to use.

What are the symptoms of vitamin D deficiency?

It is common for people to be unaware that they are vitamin D deficient until they start experiencing related health problems, particularly since it is not standard medical practice to screen people for vitamin D deficiency.

Over an extended period of time, a lack of vitamin D can lead to complications, which predominantly comprise of skeletal disorders relating to the growth and strength of the bones. These include osteomalacia (softening of the bones – also called ‘rickets’ in children) and osteoporosis (increased bone fragility). This increases the likelihood of breaking a bone at any age.

Vitamin D deficiency prevention & treatment

Vitamin D can be gained through many common, easily-accessible sources.


Although it is difficult to get sufficient vitamin D from diet alone, there are certain foods which are a good source of it. Foods high in vitamin D include:

  • Fatty, oily fish like salmon, sardines, mackerel and fresh tuna
  • Egg yolks
  • Liver
  • Red meat
  • Fortified foods, for example foods that have had vitamins or minerals added that weren’t originally in the food. These may include certain spreads, orange juice, and breakfast cereals.

Being on a restricted diet such as a strict vegan diet makes it more challenging to increase vitamin D intake through diet. However, newer food nutrition labels can be used for guidance as they show the amount of vitamin D contained in a particular food item.


Determining how much sunlight an individual needs is difficult because it depends upon a number of factors including how much skin is exposed, skin colour and strength of the sun light. However, most people can make enough vitamin D from being out in the sun daily for short periods (20-30 minutes) with their forearms, hands or lower legs uncovered and without sunscreen, from late March or early April to the end of September.

It is important not to have too much sun though and ensure that your skin does not burn or turn red.


Vitamin D intake can be increased with supplements, which are widely available from chemists and supermarkets in tablet form. Vitamin D drops are also available for infants, which can be obtained free of charge through the NHS’s ‘Healthy Start Scheme’ for qualifying households.

It is recommended that you consult your GP before taking supplements, particularly if you have pre-existing medical conditions or are currently on medication.

How long does it take to recover from vitamin D deficiency?

The strength and length of treatment depends on age, blood vitamin D levels, and the cause for low levels. In general, treatment dosage can be reduced after 6 to 8 weeks of treatment.

Can low vitamin D cause neurological symptoms?

Low vitamin D levels may be associated with neurological symptoms such as body pains, muscle weakness, and cognitive decline. Although the evidence is not strong some clinical studies have highlighted that low vitamin D levels can lead to an increased risk of diseases pertaining to the central nervous system (CNS).

Can lack of vitamin D cause weight gain?

Vitamin D deficiency itself is unlikely to cause weight gain. However, certain symptoms such as fatigue, muscle pain, and joint and bone weakness can lead to decreased levels of physical activity, which can in turn result in weight gain.

Vitamin D and coronavirus

Most of the population has been spending a lot more time indoors than usual due to COVID-19 and the various restrictions associated with the outbreak. This means our vitamin D levels will most likely be affected due to the lack of direct exposure to sunlight. Therefore, now is a crucial time to think about increasing our intake of vitamin D.

Additionally, there have been some reports about vitamin D reducing the risk of virus infections including coronavirus.  However, there is not enough evidence to recommend taking vitamin D to prevent or treat COVID-19.

How can I test my vitamin D levels?

As it is not standard medical practice to screen people for vitamin D, it can be difficult to get your levels tested unless you suffer from serious associated health complications. However, we at Bluecrest offer a range of packages that include vitamin D readings so you can easily find out and monitor your vitamin D levels.

At Home

You can test your vitamin D levels from the comfort of your own home with our Total Home Test Kit, which also includes 33 key readings including a full blood count, key blood markers, immunity readings, as well as thyroid, liver and kidney function. All you need to do is order your kit, take your own sample, send it back in our pre-addressed return envelope, and wait to receive your results online within 8 days.

At a clinic

Alternatively, you can book a health check with one of our Certified Healthcare professionals at one of over 2,000 mobile clinics nationwide. We have two packages that include vitamin D readings:

  •       Essential Energy & Fatigue Plus: includes advanced vitamin deficiency checks (including vitamin D), a full blood count, and an advanced thyroid function check to help assess the impact your lifestyle and diet is having on your energy levels.
  •       Nutritional Therapy Plan: focuses on a “Eat Yourself Healthy” approach tailored to your health check results. We recommend this plan if you are also struggling with weight management, Irritable Bowel Syndrome, low mood and anxiety, fertility problems or chronic fatigue.