Vitamin D Deficiency Fatigue: What you need to know

Vitamin-D-Mangel Müdigkeit: Was du wissen musst

Do you suffer from persistent fatigue that cannot be attributed to insufficient sleep? Among other possible causes, you may be suffering from a vitamin D deficiency. Vitamin D is essential for our body and ensures, among other things, a balanced metabolism, a strong immune system and mental well-being.

According to the Robert Koch Institute, more than 60 percent of Germans suffer from a vitamin D deficiency (1). Persistent tiredness, depression, concentration problems, a weak immune system - there are numerous indications of a vitamin D deficiency. In this article we would like to explain how you can find out whether your tiredness indicates a vitamin D deficiency and what you can do about it can. We also show other causes of persistent fatigue.

the essentials in brief

  • Vitamin D is both a fat-soluble vitamin and a hormone and ensures an intact immune system, a healthy metabolism and mental well-being. With sufficient sunlight, the body produces the vitamin D it needs itself.
  • Persistent tiredness, symptoms of exhaustion and many other - mostly very unspecific - symptoms can indicate a vitamin D deficiency. To be on the safe side, you should have a blood test done if you suspect it. If a vitamin D deficiency is confirmed, you can improve the value by taking vitamin D supplements.
  • In addition to a vitamin D deficiency, there are other causes of fatigue. To find out the cause, you should examine your diet and lifestyle. Enough sleep, a healthy diet and sufficient exercise are important to feel alert and fit.

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Vitamin D Deficiency Fatigue: What you should know

In the following, we explain the most important things you should know about vitamin D deficiency and fatigue. After reading the guide, you will have more clarity about whether your fatigue indicates a vitamin D deficiency and what you can do about it.

What is vitamin D?

Vitamin D is a fat-soluble vitamin that has a hormone-like effect. For this reason and because we cannot get it primarily through food, it is also referred to as a hormone. The body needs sunlight to produce vitamin itself. There are two forms of vitamin D: vitamin D₂ (ergocalciferol) and vitamin D₃ (cholecalciferol) (2) With sufficient sunlight, the body can produce most of the vitamin D it needs (80 to 90 percent) itself. The body then converts it into a hormone called calcitriol. With only 10 to 20 percent, diet has a relatively small share in the supply of vitamin D.

Does fatigue indicate a vitamin D deficiency?

Do you suffer from insomnia, tiredness and symptoms of exhaustion? These could be the first signs of a vitamin D deficiency. The main issue here is a chronic feeling of tiredness, which does not decrease even with sufficient sleep. Symptoms such as lack of motivation, lack of concentration and lack of energy can also occur(3).

These symptoms are fairly non-specific and may indicate other diseases as well. To be on the safe side, you should talk to your family doctor and have your blood tested, including your vitamin D level.

There are now test kits for use at home. You take blood by pricking your finger and send the sample to the specified laboratory. A few days later you will get the result.

A 2017 study examined the impact of vitamin D on sleep quality. The participants (aged 20 to 50 years) with insomnia each received a vitamin D supplement or a placebo. As a result, the participants who received vitamin D had significantly better sleep quality, longer sleep duration, and less time to fall asleep compared to the placebo group (4.5">.

What other signs are there of a vitamin D deficiency?

Tiredness and exhaustion can have different causes. In connection with other typical symptoms, a vitamin D deficiency is very likely. As already mentioned, you should still contact your family doctor first if you suspect this.

Other signs of a vitamin D deficiency are:

  • depression
  • weak immune system
  • dizziness and circulatory problems
  • nervousness
  • hair loss
  • Cravings for sweets
  • lack of motivation
  • lack of concentration
  • muscle weakness
  • persistent joint or bone pain
  • Headache

What are the causes of vitamin D deficiency?

In winter, the solar radiation in our latitudes is often too weak for sufficient vitamin D production.

In addition, nowadays we spend most of our time indoors and cover our bodies completely with clothing, especially in the colder months. As a result, fewer UVB rays reach the skin, which are necessary for the production of vitamin D (7).

Other factors that can cause vitamin D deficiency include (2):

  • Disorders that affect fat digestion and absorption (for example, celiac disease, bile acid deficiency, or pancreatic insufficiency)
  • certain medications such as antihypertensives, antiestrogens, cytostatics, antiepileptics and phytopharmaceuticals malnutrition
  • increased vitamin D requirement (pregnancy and lactation, children) increased excretion of vitamin D via the kidneys (renal insufficiency, nephrotic syndrome)
Woman is tired in bed

Persistent tiredness and feelings of exhaustion can be the first signs of a vitamin D deficiency (Image sources: Kinga Cichewicz / unsplash)

Should I take vitamin D supplements?

Whether taking vitamin D supplements is right for you depends first on what is causing the vitamin D deficiency. If not spending enough time in the sun is the cause, it can help if you stay in the sun regularly. The skin should get enough sun, but not too much, so as not to increase the risk of skin cancer.

We can only cover a small proportion of the required vitamin D requirement through food. However, you can support your vitamin D level by regularly eating foods that are rich in vitamin D.

If your vitamin D level is so low that you cannot improve it with additional sunlight or certain foods, vitamin D supplements can be useful. Before you reach for such preparations, please talk to your doctor whether or which preparations are suitable for you and which dosage is the right one.

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How much vitamin D do people need?

The amount of vitamin D required depends on height, weight and metabolism. For "healthy men" (approx. 80 kg body weight) the daily requirement is around 4000 IU (100 µg)(9). This requirement has to be covered almost exclusively by the sun - on average, only about 160 IU (4 µg) of vitamin D per day is absorbed through food.

The German Society for Nutrition (DGE) recommends, depending on the skin type, the following duration of sun exposure in our latitudes to ensure sufficient vitamin D production:

season Skin type I/II Skin type III
March to May 10 to 20 minutes 15 to 25 minutes
June to August 5 to 10 minutes 10 to 15 minutes
September to October 10 to 20 minutes 15 to 25 minutes

Which dosage and which preparation are correct for a vitamin D deficiency?

The dosage should be high enough to compensate for vitamin D deficiency, but not too high to risk overdosing. Please talk to your family doctor about this. In the following you will find an overview of various preparations and their dosage, which can serve as a guide(8,10">.

Goal dosage
Filling up if there is a shortage 1 x 50,000 IU then 10,000 IU per day for 4 weeks
Maintaining vitamin D levels in summer 400 to 2000 IU
prevention in winter 3000 to 5000 IU

The German Society for Nutrition (DGE) recommends 20 micrograms (800 international units IU) per day when there is insufficient sun exposure (especially between October and February)(11). There are studies that consider this value too low and recommend that adults between the ages of 19 and 50 need at least 600 IU of vitamin D per day. In order to have enough vitamin D in the long term, it is recommended to take 1,500 - 2,000 IU daily.

In the case of an existing deficiency, a short-term intake of up to 10,000 IU daily may be advisable (12).

What side effects can occur if I take too much vitamin D?

Before you reach for vitamin D preparations, you should be sure through a medical report that you have a deficiency. If you take additional vitamin D even though your body is sufficiently supplied, an overdose can occur because it is not excreted in the urine. Overdose can cause nausea, vomiting, abnormal heart rhythms, and impaired consciousness, and in the long run, cause weight loss, kidney stone formation, and organ damage (11,12).

Vitamin D capsule in hand

For the right dosage, you should talk to your doctor. This is the only way you can be sure that there will be no overdose. (Image sources: Daily Nouri / unsplash)

What alternative causes are there for fatigue?

If you suffer from persistent fatigue, there are other factors in addition to a vitamin D deficiency that can be the cause. Sometimes just making small lifestyle changes can be enough. If you have persistent symptoms and other symptoms, you should consult a doctor.

Below are some factors that can cause tiredness and symptoms of fatigue:

  • Diet: A wrong diet can lead to tiredness and listlessness. Fatty, high-calorie food, obesity and malnutrition can be the cause of sleep problems and tiredness.
  • Sleep quality: Sleep disorders and a lack of enough sleep can lead to severe fatigue. Therefore, you should clarify the causes of insufficient sleep. Toxic and pollutants in the environment and various diseases (such as respiratory diseases, sleep apnea) can affect the quality of your sleep.
  • Lack of exercise: Regular exercise and sports are not only important for your health, cardiovascular system and body, but also contribute to restful sleep.
  • Psyche, stress: (Psychic) ​​stress, anxiety disorders or even depression can lead to sleep disorders and feelings of exhaustion. If the problems persist, you should speak to a family doctor or psychotherapist.
  • Alcohol, nicotine, caffeine: If you are persistently tired or have poor sleep, you should avoid alcohol, nicotine and caffeine, at least for a while. Make sure you drink enough water or tea.
  • Physical causes: If you are tired and have additional symptoms such as impaired physical/mental performance, night sweats, dry mucous membranes, blood in the stool or swollen lymph nodes, you should consult a doctor. This can rule out the possibility of serious illnesses.

Overall, you should spend as much time as possible in the fresh air and in the sun. You should also ensure a healthy lifestyle, a balanced diet and sufficient exercise.

If you suspect that you are suffering from a vitamin D deficiency, you should first talk to your doctor before you take vitamin D supplements on your own. Overdose can cause side effects and long-term damage.


In our latitudes, many people suffer from a vitamin D deficiency because the body needs sufficient sunlight to meet the vitamin D requirement. Persistent tiredness combined with other symptoms can generally indicate a vitamin D deficiency. Other symptoms are, for example, listlessness, difficulty concentrating, depression, a weak immune system, etc. The symptoms are usually very unspecific and can also have other causes.

If you suspect it, you should go to your family doctor and have a blood test done to be on the safe side. If the vitamin D value is too low, the doctor can prescribe you appropriate preparations. Otherwise, he will carry out further investigations to find the cause of the tiredness. In general, a healthy lifestyle (exercise, fresh air, enough sleep) and a balanced diet contribute to your well-being. The symptoms are usually very unspecific and can also have other causes.


  1. Robert Koch Institute (2016). Vitamin D status of adults in Germany
  2. HK Biesalski, P Grimm, and S Nowitzki-Grimm (2017). Pocket Atlas Nutrition
  3. Nowak A, Boesch L, Andres E, et al. (2017). Effect of vitamin D3 on self-perceived fatigue: A double-blind randomized placebo-controlled trial
  4. MS Majid, HS Ahmad, H Bizhan, HZM Hosein, and A Mohammad (2018). The effect of vitamin D supplement on the score and quality of sleep in 20–50 year-old people with sleep disorders compared with control group
  5. J. Massa et al. (2015). Vitamin D and actigraphic sleep outcomes in older community-dwelling men: the MrOS sleep study
  6. DAK Health (2017). Tired Germany: Sleep disorders are increasing significantly
  7. M.F. Holick (2008). Deficiency of sunlight and vitamin D
  8. Heaney RP, Davies KM, Chen TC, Holick MF, Barger-Lux MJ (2003). Human serum 25-hydroxycholecalciferol response to extended oral dosing with cholecalciferol
  9. Stamp TC, Haddad JG, Twigg CA (1977). Comparison of oral 25-hydroxycholecalciferol, vitamin D, and ultraviolet light as determinants of circulating 25-hydroxyvitamin D
  10. German Nutrition Society (2020) Vitamin D
  11. MF Holick et al. (2011). Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline
  12. A Schek (2013). Nutritional science compact: Compendium of nutritional science for students of nutritional science
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