Vitamin D Deficiency: Symptoms & Treatments

[Article updated on 19/09/2023]

Rickets, osteomalacia, muscle weakness, cardiovascular disease, autoimmune diseases… These are all possible consequences of a vitamin D deficiency. This nutrient occupies an important place among the elements that make the body function. In this article, I will help you discover a little more about this very common disorder which affects more than a billion people worldwide.

Before reading on

I’m not an expert in this field, but I am passionate about nutrition and health.

The articles you’ll find on my site are the result of in-depth research that I’d like to share with you. However, I would like to stress that I am not a health professional and that my advice should in no way replace that of a qualified physician. I’m here to guide you, but it’s important that you consult a professional for specific questions or medical concerns. Your well-being is important. So be sure to consult the appropriate experts and take the best possible care of yourself.

What is vitamin D deficiency?

Vitamin D deficiency or hypovitaminosis D results in having a concentration of 1,25-hydroxyvitamin-D lower than 20 nanogram per milliliter (ng/mL) in the blood.

The sunshine vitamin is a unique nutrient. On the one hand, it acts like hormones. On the other hand, it is produced by the body itself through exposure of the skin to the sun. Once synthesized, it must still be converted into its active form called 1,25-hydroxyvitamin-D or calcitriol to be operational.

Vitamin D has two main functions:

  • It helps the body in the absorption of calcium and phosphorus;
  • It controls the secretion of parathyroid hormone, a hormone responsible for bone resorption.
Everything you need to know about hypervitaminosis D
Vitamin D is produced by the body itself through exposure of the skin to the sun.

This vitamin helps maintain normal levels of calcium and phosphorus in the blood and thus contributes to bone health. It maintains good muscle condition and improves the immune system. It also prevents certain cancers and diabetes and many others.

Possible causes

Hypovitaminosis D can occur for various reasons: medical reasons, geographic location, diet, hygiene and lifestyle.

Diet low in vitamin D

Unlike other nutrients, foods rich in vitamin D are few in number. People following a restricted diet such as vegetarians or those allergic to foods containing vitamin D are at high risk of deficiency. The same goes for infants who only consume breast milk, this nutrient being almost non-existent in the latter.

Limited sun exposure

Ultraviolet B from the sun is the main element in the production of vitamin D by the body. People who are indoors too often, always sheltered from the sun, those who always wear sunscreen or those who cover themselves from head to toe risk hypovitaminosis D. But other people are also at risk, especially those with limited access to the sun due to their geographic location or the season.

Inability of the body to absorb vitamin D

Nutrients are absorbed by the small intestine. But certain diseases such as celiac disease, cystic fibrosis or Crohn’s disease prevent the intestine from functioning properly and thus absorbing nutrients. Certain surgeries also, notably obesity interventions such as gastric bypass, reduce the quantity of nutrients that can be consumed and can lead to a deficiency.

Skin color

Studies have shown that dark-skinned individuals do not synthesize as much vitamin D as those with light skin. This is because melanin levels are higher in people with darker skin tones.

Everything you need to know about hypervitaminosis D
Studies have shown that dark skin does not synthesize as much vitamin D as light skin.

The darker the shade, the more melanin there is and the less vitamin D it produces. Therefore, people with dark skin should be exposed to the sun longer than those with fair skin.


Taking certain medications can lower the level of vitamin D in the blood. Here are some examples:

  • Laxatives;
  • Steroids: prednisone;
  • Cholesterol-lowering medications: cholestyramine, colestipol;
  • Antiepileptics: phenobarbital, phenytoin;
  • Medicines for tuberculosis: rifampicin;
  • Medications for weight loss: orlistat.

Inability of the body to convert vitamin D into its active form

The liver and kidneys are responsible for converting vitamin D into its active form by producing the corresponding enzymes. In case these organs are damaged due to disease, the transformation cannot take place. And without being in its active form, this element cannot perform its job.

Obesity and overweight

In the case of the chronic disease of obesity, vitamin D is stuck in fat cells preventing them from acting on the body. Obesity is often linked to health problems. Anyone with a body mass index greater than 30 kg/m2 is exposed there.


The body’s ability to produce vitamin D decreases with age. This is due to impaired kidney function. As a result, the body will also have difficulty absorbing calcium and phosphorus.

What are the symptoms of vitamin D deficiency?

Hypovitaminosis D may have no symptoms. The signs may vary depending on the degree of the deficiency. It can cause rickets in children or osteomalacia in adults when the deficiency is very severe. Aside from this, people suffering from vitamin D deficiency may experience the following symptoms:

  • Tiredness ;
  • Bone pain;
  • Pain, weakness and muscle cramp;
  • Weight gain ;
  • Depression and anxiety;
  • Slow healing after injury, surgery or infection;
  • Often falls ill;
  • Hair loss.
Everything you need to know about hypervitaminosis D
Hypovitaminosis D may not be accompanied by any symptoms.

What to do in case of deficiency?

If you think you are deficient in vitamin D, consult your doctor right away so that you can follow the appropriate treatment. He will guide you and prescribe supplements if necessary. Self-medication is strongly discouraged. The only thing you can do in the meantime is eat foods rich in vitamin D and get out in the sun. However, the advice of a doctor will always be necessary, even when it comes to sunbathing.

How to diagnose a shortage?

Blood testing is the only way to ensure whether an individual is deficient in vitamin D or not. For hypovitaminosis D, the test consists of analyzing the serum level of 25-hydroxyvitamin-D in the blood. The normal level of calcitriol in the blood is greater than or equal to 20 ng/mL. If the value is between 12 to 20 ng/mL, the diagnosis is vitamin D insufficiency. The doctor confirms this deficiency when the calcitriol level is less than 12ng/mL.


Treatment mainly involves taking supplements. These products exist in 2 formats: vitamin D2 called ergocalciferol, it is of plant origin and vitamin D3 called cholecalciferol of animal origin. The dosage and duration of treatment varies depending on the stage of the deficiency and the patient’s situation.

For example, for an individual with no nutrient absorption problems, the dosage is approximately 1,250 micrograms (mcg) once or twice a week, for 6 to 8 weeks. The dose is then reduced by 20 to 25 mcg.

Everything you need to know about hypervitaminosis D
Treatment mainly involves taking vitamin D supplements.

The supplement exists in several formats: tablets, liquids, powders… It is even possible to receive an injection. Taking calcium in parallel with the vitamin D supplement is also recommended. Aside from this, the doctor will also recommend consuming certain foods and going outside from time to time so that the skin can come into contact with the sun’s rays.

Blood tests may be requested throughout treatment to adjust the dosage of supplements in accordance with the level of calcitriol in the blood.

Foods to favor

Foods rich in vitamin D are mainly foods of animal origin:

  • Oily fish: mackerel, sardines, salmon, trout, tuna, herring;
  • Liver of beef ;
  • Egg yolk ;
  • Cheese (Emmental);
  • Soy milk ;
  • Mushroom ;
  • Foods fortified with vitamin D: cereals, orange juice, cow’s milk, margarine, etc.