Vitamin D
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Vitamin D
In recent years there has been a considerable increase in vitamin D supplements, and today we try to understand why.
Vitamin D forms naturally in the body in the skin through irradiation, and is then converted in the liver and subsequently in the kidneys.
Functions of vitamin D
The main role of vitamin D is to regulate the intestinal absorption of calcium and phosphorus, supporting the normal formation and mineralisation of bone. Vitamin D is also involved in the process that ensures normal muscle contraction, and it interacts with the immune system, exerting an immunomodulatory effect.
How to find out your vitamin D levels
A blood test will tell you your vitamin D levels. The table below gives the reference values:
What does a vitamin D deficiency lead to?In many people vitamin D deficiency causes no symptoms at all. A severe deficiency causes rickets in children and osteomalacia in adults. Low vitamin D levels can also lead to reduced muscle strength and widespread pain.
§IU: International Units *Adapted from Saggese et al. 2018
When is vitamin D used to prevent or treat deficiency?
Vitamin D is recommended:
• for elderly residents of care homes
• for pregnant or breastfeeding women
• for people with osteoporosis from any cause, or with confirmed bone diseases for which remineralising therapy is not indicated
Use after measuring 25(OH)D is recommended:
• for people with serum 25(OH)D levels < 20 ng/mL and symptoms attributable to hypovitaminosis (weakness, muscle pain, widespread or localised pain, frequent unexplained falls)
• for people diagnosed with hyperparathyroidism secondary to vitamin D deficiency
• for people with osteoporosis from any cause, or with confirmed bone diseases, for whom correcting the deficiency should come before starting remineralising therapy.
• in the case of long-term therapy with drugs that interfere with vitamin D metabolism (anti-epileptics, glucocorticoids, antiretrovirals, antifungals, etc.).
• in the case of diseases that can cause malabsorption in adults (cystic fibrosis, coeliac disease, Crohn's disease, bariatric surgery, etc.).
The absorption of vitamin D involves organs such as the liver and kidneys, which can be affected by various diseases (e.g. alcoholic liver disease or renal osteodystrophy), and/or the need to follow a special diet: this explains why supplementation may be necessary. Not to mention that tanning itself, which would be the main source of vitamin D, is now under scrutiny because of skin cancers linked to UV rays.
Our recommended supplements
Vitamin D VOLCHEM 100 tablets contains only the active form of vitamin D, namely cholecalciferol or vitamin D3, of pharmaceutical grade, meaning 100% purity.
It is obtained by synthesis from dehydrocholesterol from sheep's wool, not from plant extracts. It contains no fats, artificial preservatives, gluten, lactose or sugars. Its only carrier is natural plant fibre such as cellulose.
The dose per tablet varies and takes into account:
The daily doses of one Vitamin D tablet have been approved by Europe's leading scientific authority (EFSA) for supporting bones, muscles and the immune system itself, and for reducing the risk of falling in older people.
How much vitamin D?
The daily dose recommended for the general population by EFSA - EU and FDA - USA (2023) is:
Daily oral administration of vitamin D3 can raise blood vitamin D levels by 1 ng/mL for every 100 IU - 2.5 mcg given over 2 months. In people of normal weight, 2000 IU a day would therefore be enough to bring even a significant deficiency back to normal (> 20 ng/mL) within 2-4 months.
Where this dose is not sufficient, even higher doses (e.g. 10,000-100,000 IU) could be used, taken under medical supervision.
Once normal blood levels (20-40 ng/ml) have been reached, the maintenance dose can drop to 400 - 800 IU 10-20 mcg.
Why are there also products on the market with higher IU doses of vitamin D?
As mentioned above, the maximum daily dose set by law is 2000 IU. There are medicines (not supplements) on the market with higher doses, but they should always be taken on prescription according to the person's specific deficiencies. These products are also usually taken at intervals of at least one or two weeks, unlike a supplement, which relies on regular intake to provide a continuous supply of vitamin D, but which must be lower in order to avoid possible toxic effects.
Why is it important to follow the correct dosage? What adverse health effects can an excess of vitamin D cause? Why should you always consult a doctor before taking vitamin D medicines?Vitamin D is fat-soluble and therefore tends to accumulate in the human body. Taking high doses for long periods can cause serious health effects, such as hypercalcaemia and nephrolithiasis (kidney stones), and can also increase the risk of fractures in the months following the administration of vitamin D boluses (Sanders KM et al. 2010) and the risk of some cancers in populations with 25(OH)D levels > 40-50 ng/mL (IOM 2011).
For these reasons you should always consult a doctor before taking vitamin D medicines and follow the correct prescribed dosage. It should also be remembered that vitamin D overdose during the first 6 months of pregnancy can have toxic effects on the foetus, so in this case too these medicines must only be taken during pregnancy on medical prescription.
Would you like to try a vitamin D supplement?
Discover the complete range of vitamin D tablets.
In recent years there has been a considerable increase in vitamin D supplements, and today we try to understand why.
What is vitamin D?
Vitamin D is a fat-soluble prohormone produced in the skin through the action of UVB rays. Sun exposure is the main natural source of vitamin D; however, it can also be obtained through the diet. Vitamin D forms naturally in the body in the skin through irradiation, and is then converted in the liver and subsequently in the kidneys.
Functions of vitamin D
The main role of vitamin D is to regulate the intestinal absorption of calcium and phosphorus, supporting the normal formation and mineralisation of bone. Vitamin D is also involved in the process that ensures normal muscle contraction, and it interacts with the immune system, exerting an immunomodulatory effect.
How to find out your vitamin D levels
A blood test will tell you your vitamin D levels. The table below gives the reference values:
| Blood levels of vitamin D | Treatment (ISS 2018) |
| < 10-12 ng\mL | "Intensive" replacement therapy (vitamin D supplementation required) |
| 10-12 ng\mL | Replacement therapy recommended |
| 20-40 ng\mL | Normal levels (do not change the current status: do not start therapy, or continue the therapy in progress) |
| 40-50 ng\mL | Do not start therapy, or reduce it as a precaution |
| >50 ng\mL | Reduce the therapy dose or stop it |
What does a vitamin D deficiency lead to?
What are the natural sources of vitamin D?
Effective exposure to sunlight and dietary intake of vitamin D are the main factors that determine serum levels of 25(OH)D.
Effective exposure to sunlight and dietary intake of vitamin D are the main factors that determine serum levels of 25(OH)D.
- Sun exposure
The skin produces vitamin D when stimulated by UV rays with a wavelength between 290 and 315 nm. Exposure must be direct, not through glass.
Sun exposure does not cause hypervitaminosis, because excess vitamin D is destroyed in the skin.
Exposure in a swimsuit that leads to mild erythema is equivalent to taking 10,000–25,000 IU of vitamin D (NB - NRV = 5 mcg = 200 IU).
In young adults, exposing about 25% of the body surface (face and arms) to the summer sun without sunscreen for 15 minutes 2-3 times a week is equivalent to an oral dose of 25 mcg or 1000 IU of vitamin D.
UV-generating devices (sunbeds) are available on the market that emit 2 to 6% beta-type radiation at a wavelength useful for producing vitamin D.
Study results are not consistent, and there are significant risks regarding the development of skin cancers.
The FDA recommends caution: it favours oral intake of vitamin D over exposure to sunbeds.
Sun exposure does not cause hypervitaminosis, because excess vitamin D is destroyed in the skin.
Exposure in a swimsuit that leads to mild erythema is equivalent to taking 10,000–25,000 IU of vitamin D (NB - NRV = 5 mcg = 200 IU).
In young adults, exposing about 25% of the body surface (face and arms) to the summer sun without sunscreen for 15 minutes 2-3 times a week is equivalent to an oral dose of 25 mcg or 1000 IU of vitamin D.
UV-generating devices (sunbeds) are available on the market that emit 2 to 6% beta-type radiation at a wavelength useful for producing vitamin D.
Study results are not consistent, and there are significant risks regarding the development of skin cancers.
The FDA recommends caution: it favours oral intake of vitamin D over exposure to sunbeds.
- Dietary intake
Most foods contain only small amounts of vitamin D, so diet alone cannot be considered an adequate source. Vitamin D is relatively stable and is little affected by storage and cooking. The table below lists a number of foods with their vitamin D content:
| Table 2. Vitamin D content (IU/100 g or IU/l) of some foods*. | Average vitamin D content |
| Cow's milk | 5-40 IU/L |
| Butter | 30 IU/100 g |
| Yoghurt | 2.4 IU/100 g |
| Cream | 30 IU/100 g |
| Cheese | 12-40/100 g |
| Pork | 40-50 IU/100 g |
| Beef liver | 40-70 IU/L |
| Dentex, cod, gilthead bream, smooth-hound, sole, trout, salmon, herring | 300-1500/100 g |
| Cod liver oil | 400 IU/5ml (1 teaspoon) |
| Egg yolk | 20 IU/100 g |
When is vitamin D used to prevent or treat deficiency?
Vitamin D is recommended:
• for elderly residents of care homes
• for pregnant or breastfeeding women
• for people with osteoporosis from any cause, or with confirmed bone diseases for which remineralising therapy is not indicated
Use after measuring 25(OH)D is recommended:
• for people with serum 25(OH)D levels < 20 ng/mL and symptoms attributable to hypovitaminosis (weakness, muscle pain, widespread or localised pain, frequent unexplained falls)
• for people diagnosed with hyperparathyroidism secondary to vitamin D deficiency
• for people with osteoporosis from any cause, or with confirmed bone diseases, for whom correcting the deficiency should come before starting remineralising therapy.
• in the case of long-term therapy with drugs that interfere with vitamin D metabolism (anti-epileptics, glucocorticoids, antiretrovirals, antifungals, etc.).
• in the case of diseases that can cause malabsorption in adults (cystic fibrosis, coeliac disease, Crohn's disease, bariatric surgery, etc.).
The absorption of vitamin D involves organs such as the liver and kidneys, which can be affected by various diseases (e.g. alcoholic liver disease or renal osteodystrophy), and/or the need to follow a special diet: this explains why supplementation may be necessary. Not to mention that tanning itself, which would be the main source of vitamin D, is now under scrutiny because of skin cancers linked to UV rays.
Our recommended supplements
Vitamin D VOLCHEM 100 tablets contains only the active form of vitamin D, namely cholecalciferol or vitamin D3, of pharmaceutical grade, meaning 100% purity.
It is obtained by synthesis from dehydrocholesterol from sheep's wool, not from plant extracts. It contains no fats, artificial preservatives, gluten, lactose or sugars. Its only carrier is natural plant fibre such as cellulose.
The dose per tablet varies and takes into account:
- the requirements of the general population, from the young athlete to the over-70s, equal to 800 IU or 20 micrograms (mcg)/day;
- 2000 IU, equal to 50 mcg, is the maximum daily dose recommended by the Italian Ministry of Health;
- the risks of excessive doses of vitamin D from prolonged intakes above 2000 IU. In these cases, increased calcium absorption and bone resorption can cause hypercalcaemia, which can lead to metastatic calcification with consequent damage to the heart, blood vessels and kidneys.
The daily doses of one Vitamin D tablet have been approved by Europe's leading scientific authority (EFSA) for supporting bones, muscles and the immune system itself, and for reducing the risk of falling in older people.
How much vitamin D?
The daily dose recommended for the general population by EFSA - EU and FDA - USA (2023) is:
- 400 IU – 10 mcg for infants < 12 months
- 400 - 800 IU 10-20 mcg from 1 to 70 years of age, and during pregnancy and breastfeeding.
- 800 IU 20 mcg per day > 70 years
- 1600-2000 IU 40-50 mcg per day in the presence of hypovitaminosis (< 20 ng/ml) or predisposing conditions (see above).
Daily oral administration of vitamin D3 can raise blood vitamin D levels by 1 ng/mL for every 100 IU - 2.5 mcg given over 2 months. In people of normal weight, 2000 IU a day would therefore be enough to bring even a significant deficiency back to normal (> 20 ng/mL) within 2-4 months.
Where this dose is not sufficient, even higher doses (e.g. 10,000-100,000 IU) could be used, taken under medical supervision.
Once normal blood levels (20-40 ng/ml) have been reached, the maintenance dose can drop to 400 - 800 IU 10-20 mcg.
Why are there also products on the market with higher IU doses of vitamin D?
As mentioned above, the maximum daily dose set by law is 2000 IU. There are medicines (not supplements) on the market with higher doses, but they should always be taken on prescription according to the person's specific deficiencies. These products are also usually taken at intervals of at least one or two weeks, unlike a supplement, which relies on regular intake to provide a continuous supply of vitamin D, but which must be lower in order to avoid possible toxic effects.
Why is it important to follow the correct dosage? What adverse health effects can an excess of vitamin D cause? Why should you always consult a doctor before taking vitamin D medicines?Vitamin D is fat-soluble and therefore tends to accumulate in the human body. Taking high doses for long periods can cause serious health effects, such as hypercalcaemia and nephrolithiasis (kidney stones), and can also increase the risk of fractures in the months following the administration of vitamin D boluses (Sanders KM et al. 2010) and the risk of some cancers in populations with 25(OH)D levels > 40-50 ng/mL (IOM 2011).
For these reasons you should always consult a doctor before taking vitamin D medicines and follow the correct prescribed dosage. It should also be remembered that vitamin D overdose during the first 6 months of pregnancy can have toxic effects on the foetus, so in this case too these medicines must only be taken during pregnancy on medical prescription.
Would you like to try a vitamin D supplement?
Discover the complete range of vitamin D tablets.
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