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Vitamin D Deficiency: What Are the Symptoms of Low Vitamin D?

Sarah Vordermeier

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Vitamin D deficiency – also known as vitamin D3 deficiency – affects a hefty one billion people around the world. We can only acquire enough of this essential vitamin – also known as the sunshine vitamin – with sufficient exposure to the sun or by taking the right vitamin D supplements.

Hair loss, depression, fatigue, skin diseases, and cancer are some of the short-term and long-term effects associated with vitamin D deficiency. Studies have shown that vitamin D plays a role in numerous processes in the body. It impacts bone, muscle, immune system, and blood vessel function – and much more. As a result, vitamin D has been a hot topic not only among scientists and physicians over recent years, but also in the media, in weekly magazines, television programs and social media.

Despite the media hype and the new awareness surrounding vitamin D, few people manage to take in enough. It is estimated that one billion people in the world have low vitamin D intake. According to the National Health and Nutrition Examination Survey (NHANES), low vitamin D levels were found in 41.6 percent of 4,495 US participants in a vitamin D deficiency study,[1] so it’s possible that almost half of US citizens are vitamin D deficient. 

What is the function of vitamin D in our body, and how does a deficiency affect us? We’ll cover all this and tell you more about vitamin D deficiency symptoms, vitamin D testing, optimal vitamin D intake, and which supplements you can take to ensure that you are optimally supplied with vitamin D.

What Is Vitamin D?

Vitamin D is a fat-soluble vitamin, with experts also referring to it as a hormone. This is because it has a hormone-like effect, and we don’t consume it primarily through our diet, as is otherwise normal with other vitamins. Instead, our body produces vitamin D itself, but requires UVB radiation from the sun to produce it. It is therefore not for nothing that vitamin D is also called the sunshine vitamin.

The two most important forms of vitamin D are vitamin D₂ (ergocalciferol), which is found in plants, and vitamin D₃ (cholecalciferol), also called 25-(OH)-D.[2] The latter form of vitamin D is found in animal tissue. Our bodies produce vitamin D when sunlight breaks down the chemical bonds of the chemical precursor of vitamin D, 7-dehydrocholesterol, which, itself, is found in our skin.

There, the active form of the vitamin – namely, vitamin D3 – is produced, and this in turn becomes 25-hydroxy-cholecalciferol (25-OH-D), the storage form of vitamin D, which is then stored in our muscles and adipose tissue. In the kidney, 25-OH-D is converted to 1,25-(OH)2-D, which is transported through our blood to our intestine, bones, muscles, immune system, and cells where it carries out further important bodily functions.[5]

What Is the Function of Vitamin D in Our Body?

Vitamin D is involved in numerous processes within the body, attributable particularly to its dual role as both a vitamin and a hormone. Among its most important tasks is its role in bone metabolism and muscle development and function. In addition, vitamin D boosts our immune system health and protects blood vessels.[2]

Other functions of vitamin D include:

  • controlling calcium and phosphate absorption in the small intestine;
  • regulating more than 200 genes;
  • promoting heart muscle function;
  • functioning as a hypotensive mediator; and
  • promoting skeletal development in children.
graphic explaining the function of vitamin D in our body

How Much Vitamin D Do I Need?

With vitamin D, it is important to maintain sufficient levels, and a reliable daily dose is difficult to determine because we also receive different amounts of vitamin D in different seasons. The best way is to measure vitamin D levels in your blood. You can have your 25-(OH)-D blood levels measured – this might be given, for instance, in nanograms per milliliter.[34]

  • Your vitamin D levels are sufficient if your concentration of vitamin D is 30 nanograms per milliliter of blood.
  • Values below 11 nanograms per milliliter are considered to be critical and can encourage disorders such as bone loss – also known as osteoporosis.
  • Some researchers argue that 60 nanograms or more of vitamin D per milliliter of blood will ensure you enjoy all health benefits the sunshine vitamin has to offer.

Is Vitamin D Deficiency Serious?

It is estimated that about one billion people globally are affected by vitamin D deficiency.[9, 10] Various studies have linked vitamin D deficiency to chronic diseases such as osteoporosis, diabetes, cancer, depression, cardiovascular disease, and a weakened immune system.[14–17]

Who Is Affected by Vitamin D Deficiency?

In general, vitamin D deficiency occurs in all age groups and social groups, and in areas as diverse as Europe, South America, and the Middle East. That being said, you should be aware that there are certain risk groups. If you belong to one of these groups, you should regularly check your vitamin D levels and, if necessary, take supplements.

The risk groups include:[18]

  • people who are predominantly indoors or who cover their bodies when they are outdoors;
  • pregnant women, since they also have a higher vitamin D requirement
  • people with a dark skin type because their bodies produce less vitamin D than people with fair skin
  • elderly people, since vitamin D production decreases significantly in old age – and they may often not be outdoors, for mobility reasons
  • babies, since the vitamin D content in breast milk is low and they should not be exposed to direct sunlight

To find out more about the ideal diet during breastfeeding and pregnancy – as well as which other important vitamins and minerals your body needs – head over to our dedicated Health Portal blog article.

banner to vitamin D deficiency test

Vitamin D Deficiency Causes: What Do I Need To Know?

Low vitamin D levels occur because we do not get enough sun. While our ancestors stayed primarily outdoors, we spend most of our time indoors. And we also cover our bodies with clothing and protect ourselves with sunscreen. All of this reduces the effects of UVB on the skin – and that’s precisely what our body needs to produce vitamin D.[19]

Did you know that by applying a sunscreen with a sun protection factor of 30, vitamin D synthesis in our skin is reduced by more than 95 percent?[31]

Several other factors can also interfere with our body’s vitamin D production. These vitamin D deficiency causes, include – for example:[2]

  • diseases that impair fat digestion and ingestion, such as celiac disease, bile acid deficiency, or pancreatic insufficiency; and
  • certain medications such as antihypertensives, antiestrogens, cytostatics, antiepileptics, and herbal medicines.

Vitamin D Deficiency Causes: Does Vitamin D Deplete with Age?

Elderly gentleman sat outside on a bench in the sunshine

From 60 years onwards, vitamin D deficiency is particularly common. This is not always because older people rarely go outdoors – their body in fact produces down to four times less vitamin D than younger people. If you are over 60, you should regularly check your vitamin D levels and counter any deficiencies with supplements.[22-25]

Taking the right dosage of vitamin D supplements is incredibly beneficial, as it can prevent or alleviate many health complaints encountered frequently in old age. Positive effects confirmed in studies include:[22, 26-29]

  • reduced risk of bone fractures;
  • better cardiovascular health;
  • reduced cancer risk, such as colon cancer;
  • better balance; and
  • greater muscle power.

What Are Common Vitamin D Deficiency Symptoms?

Vitamin D deficiency symptoms are rarely noticeable; they are often generic and hidden, and include fatigue, muscle fatigue, musculoskeletal pain, and headaches.[1] As a result, many people do not notice they suffer from low vitamin D levels until it develops into more serious health conditions. A common consequence of chronic vitamin D deficiency is osteomalacia (bone softening).[19]

Those who have a severe chronic vitamin D deficiency are at an increased risk of:[19]

  • osteomalacia and osteoporosis
  • rickets in children
  • pain and weakness in the bones (osteoarthritis)
  • bone fractures in seniors over 65 (broken bones)

In addition, recent study results have associated a vitamin D deficiency with a number of diseases. The diseases often occur together with the deficiency, and researchers are still investigating how strongly vitamin D deficiency is connected with the following conditions:[20, 21]

  • hypertension and heart disease,
  • diabetes,
  • depression,
  • serious infections such as tuberculosis and chronic kidney disease, and
  • hair loss.

What Diseases Can Be Caused by Vitamin D Deficiency?

dangers of vitamin D deficiency

In recent years, scientists have spent considerable time studying how vitamin D levels impact our overall health. We’ll now present you with a series of studies that show the links between vitamin D and various diseases and health problems.

Vitamin D and Depression: How Does Vitamin D Affect Mood?

Studies have shown that vitamin D deficiency impacts mental health. Among other things, depression, stress, mood swings, and anxiety can all be linked to low vitamin D levels.[48]

The relationship between low vitamin D levels and depression has already been studied. People with depression have significantly lower vitamin D levels than people who aren’t depressed.[48] Some studies suggest that vitamin D supplements might improve depressive symptoms in people with vitamin D deficiency, but evidence gathered to date does not allow for any specific recommendations to be made.

Does Vitamin D Help with Sleep?

In 2017 Iranian scientists investigated the effect of vitamin D on sleep quality. A total of 89 participants with sleep disorders aged 20 to 50 years were administered either a vitamin D supplement or a placebo.

The result was that the participants who received vitamin D found that the quality of their sleep significantly improved, they slept for longer, and it took them less time to fall asleep compared with individuals who did not receive the vitamin D supplement. In another study, people with low vitamin D levels endured a poorer sleep quality.[49]

Besides vitamin D, there are other sleep supplements that have been proven to boost the quality of your sleep – including melatonin, magnesium, 5-HTP, and valerian – among many others. If you’re struggling with sleeping, you can discuss taking these supplements with your doctor.

Are Vitamin D and Hair Loss Linked?

For some time it has been known that vitamins and minerals affect hair growth. For instance, iron, biotin, and zinc are important for healthy hair roots.[50] Studies conducted in test tubes suggest that vitamin D might also be involved in active hair growth.

Vitamin D as such promotes the production of receptors in hair roots, which then stimulate growth. Up until now, however, no conclusive and informative clinical studies have been published that can confirm this theory.

Can Vitamin D Help Migraines?

A migraine is a severe headache that keeps on coming back. Experts now believe that migraine episodes develop as a result of inflammation in the nerves and blood vessels.[51] Researchers are currently investigating whether vitamin D supplements can inhibit the inflammatory factors that contribute to migraines. The fact that vitamin D is anti-inflammatory has been confirmed in other studies.[52]

However, at present, there are still relatively few studies in this area and the research results are still inconsistent. Some have revealed a connection between vitamin D and migraines, and in one study it was shown that taking vitamin D could reduce the frequency of headaches.[52] In other studies, however, vitamin D did not have an impact on migraines.

How Does Vitamin D Affect the Skin: Vitamin D Deficiency and Eczema

Vitamin D also seems to play a role in our skin health. The vitamin clearly contributes to wound healing and allowing our epidermis to develop properly. vitamin D deficiency may therefore contribute towards the development of skin diseases such as eczema (atopic eczema), psoriasis, and white spot disease (vitiligo).[53]

Studies have shown promising results regarding vitamin D supplementation and atopic (neuro)dermatitis. Eczema patients are very susceptible to bacterial skin infections – in one study, patients with low vitamin D levels were particularly likely to suffer from such infections.[54] Researchers are also investigating how vitamin D supplements can positively impact psoriasis and vitiligo (white spot disease).[55]

What Are the Effects of Vitamin D on Cardiovascular Health?

Vitamin D, according to research, can strengthen the heart muscle. In addition, vitamin D carries out an important role when it comes to calcium and phosphate metabolism. The sunshine vitamin ensures that calcium and phosphate are stored in the bones. If you suffer from vitamin D deficiency, calcium in particular is not stored properly and instead settles in the blood vessels, which can sometimes lead to calcification.[46]

A study published in the American Journal of Cardiology in 2012 revealed that vitamin D deficiency may increase the risk of dying from cardiovascular disease. Vitamin D supplements reduced this risk in the same study. The study authors assumed that vitamin D deficiency is a risk factor for heart disease, cardiac muscle problems, and high blood pressure.[56]

These results were confirmed by another study involving over 40,000 patients. Subjects with vitamin D levels of less than 15 nanograms per milliliter were more likely to experience hypertension, elevated blood lipid levels, heart defects, and strokes than those with vitamin D levels of 30 nanograms per milliliter.[56]

Another supplement that is known to boost your heart health is omega fatty acids. This nutrient can also be found in certain foods, such as fatty fish and coconut oil. To read more about the benefits of omega 3, head over to our Health Portal article.

Does Vitamin D Help with Osteoporosis?

Not only calcium but also vitamin D are crucial for optimal bone health. When it comes to preventing osteoporosis and bone loss or fractures, calcium and vitamin D supplementation are considered absolutely vital.

A function of vitamin D is that it regulates calcium absorption and stimulates bone resorption. If you don’t treat your vitamin D deficiency, calcium continues to be pulled from your bones, leading to rickets can occur in children and osteomalacia and osteoporosis in adults.

Bone loss generally occurs without symptoms – and osteoporosis is considered a silent disease. Fractures or injuries that have occurred due to osteoporosis or bone softening can lead to chronic pain, disability, and psychological symptoms, such as depression.[60] For more information about preventing osteoporosis and the symptoms and causes of osteoporosis, visit our Health Portal blog article.

How Does Vitamin D Affect Cancer?

Vitamin D is considered by many to be a ray of hope when it comes to preventing cancer. Study results until now, however, have proven ambiguous. Individual studies found links, for instance, between vitamin D levels and the risk of colon cancer and breast cancer.[57]

Current large-scale studies, however, found that vitamin D intake had no influence on the development of tumors. Many scientists say that more research is required before anything more concrete can be stated. Studies dealing with this topic are currently ongoing, some of which are also investigating the effects of high-dose vitamin D supplements on cancer development.

COVID-19 and Vitamin D: Is vitamin D important for the immune system?

You’ve no doubt heard a multitude of times from various sources that the global pandemic has transformed our lives in unprecedented ways. As frustrated as we may be with hearing this phrase, it is certainly true when it comes to our vitamin D levels. 

Dermatologists have warned that our new routines require vitamin D supplements. With more people working from home these days – and therefore less people commuting than before the pandemic – it is essential for us to make sure we are getting that all-important exposure to the sun. Even during the winter months! Don’t forget that travel restrictions and fear to venture abroad have meant that fewer people are willing to go on their usual summer vacation. Those vital annual vitamin D reserves might therefore be lower than normal for some people.

So, what about the importance of vitamin D supplements in the fight against the coronavirus itself? Studies are currently being conducted to inspect in further detail just how effective vitamin D could be in terms of fighting COVID-19. Currently, there only seems to be reported and unverified links between a vitamin D deficiency and the severity of the virus; however, a study published in January 2021 by BMJ Nutrition, Prevention and Health has revealed that there is no evidence of vitamin D being protective against COVID-19.[58]

Can You Test Your Own Vitamin D Levels?

Many factors are involved in regulating your supply of vitamin D and avoiding a deficiency. Without a test, it’s difficult to say how you should best optimize your intake. In order to find out if and how you should supplement vitamin D, a vitamin D Test is certainly worthwhile – especially if you belong to one of the at-risk groups.

The most common measurements are blood tests performed by a doctor. With a home health test, you can also check your levels from the comfort of your home. To do this, take a blood sample yourself by pricking your finger and sending it to a specialist laboratory. The laboratory will then analyze the level of 25-(OH)-D in your blood serum. Afterward, the lab usually sends you a results report telling you where your values are at and how to get your vitamin D levels back on track (and keep it on track) using vitamin D supplements.

You should not take any vitamin D supplements without first having a blood test. Unlike other vitamins, you cannot get rid of vitamin D through your urine. If your vitamin D levels are already good, and you still take long-term high-dose supplements, you might overdose on vitamin D. Too much vitamin D can trigger symptoms such as nausea, vomiting, cardiac arrhythmia, and dysregulation – and in the long term, weight loss, kidney stones, and organ damage.[2, 5]

What Is the Best Treatment for Vitamin D Deficiency?

what influences our vitamin D intake?

How long we need to lie in the sun to produce enough vitamin D depends on many factors, including our skin type, the latitude we live in, the time of day, and the time of year. According to experts, over summer, it usually suffices to expose our face, hands, and arms to direct sunlight three times a week for ten to twenty minutes.

To produce 400 IU of vitamin D, a person with medium-light skin (one who tans slowly and rarely gets sunburn) on the 42nd line of latitude from April to October (for example, in southern France) should expose a quarter of their skin (for example, arms, face, neck) for about three to eight minutes at midday in the sun.

Many people across the globe are not able to expose themselves to enough sun in the summer – and this is even more impossible in the winter. In winter, the sun rarely shines in northern latitudes, and its light also contains too little UVB radiation. It is barely possible to produce adequate vitamin D.[1]

Researchers and professional institutions are therefore discussing how much vitamin D we should consume via dietary supplements if an adequate supply cannot be guaranteed due to insufficient sun exposure.

Please note: do not overdo it while sunbathing. A few minutes without UV protection are useful for boosting vitamin D production, but too much direct sunlight can lead to sunburn and increase the risk of skin cancer. Curious about the ideal summer skin care regime? Check out our blog article on summer skin care and sun allergy.

Vitamin D in Our Diet: What Foods Are Highest in Vitamin D?

Our small intestine can absorb up to 80 percent of the fat-soluble vitamin D3 consumed in food.[5] Despite this, our body only absorbs relatively small amounts of vitamin D into the body this way; we only cover about 10 to 20 percent of our  daily vitamin D requirement through our diet.

This is partly due to the fact that few foods contain vitamin D, and when they do, they only contain small quantities. Vitamin D3, which is important for the body, is found almost exclusively in animal foods, and more specifically in:[2, 5]

  • fatty fish such as herring or kippers;
  • margarine and butter; and
  • milk and egg yolk.

Mushrooms and avocados also contain vitamin D – but in a form that the body can only poorly absorb. You would actually need to consume large amounts of these foods to even get close to the the lowest recommended daily requirement. For the 600 International Units recommended by the National Institutes of Health – that is, 20 micrograms, you would need for example 2,400 grams of mushrooms, four kilos of beef liver, four kilos of butter, or 80 eggs.[2]

In summary, with food alone, it is not possible to meet your daily requirement for vitamin D. Our bodies have to produce the largest proportion of vitamin D ourselves – and this simply does not work without sunlight.

Does Vitamin D Affect Vitamin K?

Vitamin K is thought to have a similar protective effect to vitamin D. Its role is to primarily prevent and treat bone and vascular diseases. Vitamin K1 is found, for instance, in green vegetables, while vitamin K2 is produced by our gut microbiome. How much vitamin K we need exactly has not yet been fully researched[41].

Again and again it has been written that when consuming vitamin D, you may find that this leads to low vitamin K levels, since both vitamins are involved in bone formation and mutually influence one another. However, this idea has not been scientifically proven.[40] Medical experts currently recommend taking supplements containing both vitamin D and vitamin K to specifically treat osteoporosis and prevent bone fractures occurring in older people.[41–43]

Vitamin D Deficiency: Symptoms and Treatment – at a Glance

What Is Vitamin D?

Vitamin D is both a fat-soluble vitamin and a hormone at the same time. It is involved in many processes in the body, including bone metabolism, muscle function, the immune system, and vascular protection.

Where Do People Get Vitamin D from?

Our body produces 80 to 90 percent of vitamin D all by itself – but to do this, it needs the UVB radiation from sunlight. To maintain our vitamin D levels, we must expose our face, hands, and arms to the sun three times a week for 10 to 20 minutes during the summer months. The remaining 10 to 20 percent we get from our diet – that is, from fatty fish, eggs, dairy products, and edible mushrooms.

Who Is Affected by Vitamin D Deficiency?

Around one billion people across the world are not adequately supplied with vitamin D. The risk groups include the elderly, pregnant women, people with darker skin types, and people who hardly ever go outdoors or cover most of their body when doing so.

What Are Typical Long-Term Vitamin D Deficiency Symptoms?

Vitamin D deficiency can have a particularly negative impact on bone health where it may promote osteomalacia and osteoporosis. Other illnesses associated with a deficiency include depression, cardiovascular disease, hair loss, skin diseases, and migraines.

How Can I Test My Vitamin D Levels?

Using a blood test, you can determine the concentration of 25-(OH)-D in your blood. This is the most significant parameter that describes your supply of vitamin D. You can measure your vitamin D levels with a home self-test. Most scientific sources recommend levels of at least 30 nanograms per milliliter of blood.

What Can I Do about a Vitamin D Deficiency?

If you have a vitamin D deficiency, it is difficult to counteract it with diet and sunbathing alone, especially during fall and winter. Dietary supplements are more effective. A daily dose of 1,000 to 2,000 International Units (IU) is recommended to maintain its levels. To correct a deficiency, higher doses may be useful.


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