Vitamin D acts as a hormone that influences the process of intestinal calcium and phosphorous absorption. Indirectly, it contributes to bone mineral density, and regulates inflammation and immune system activities. Only a small part of the amount we need comes from food, exposure to the sun is the main source, this creates the active form of vitamin D. Although vitamin D benefits the body in numerous ways, the Italian Medicines Agency (AIFA) only recommends supplements in people with Vitamin D deficiency or specific medical conditions. Generally healthy people just need to ensure they have a varied, balanced diet and spend time in the open air; supplements, whether dietary or pharmacological, may be necessary for people who seldom leave the house, such as infants and the elderly.
10-20 percent of our daily intake requirement comes from food. As well as fortified foods such as many breakfast cereals, it can be found in fatty fish (like salmon, mackerel and herring), egg yolks and liver, for example.
All the rest is formed in the skin from a cholesterol-like fat that is transformed by exposure to UVB rays. Once produced in the skin or absorbed from food, vitamin D passes into the blood where a binding protein transports it to the liver and kidneys, here it is turned into the active form the body needs.
Over the years, vitamin D deficiency has been associated with various types of disease, from diabetes to cancer, Alzheimer’s, multiple sclerosis, and more recently with severe forms of Sars-CoV-2 infection.
Although the cause-and-effect relationships have yet to be demonstrated, a theory has developed that low levels of this vitamin could be detrimental to the health, while supplementing it may have a protective and therapeutic effect against several diseases, such as Covid-19 infection and cancer. However, in light of the results of recent epidemiological studies, the Italian Medicines Agency stated in Note 96 of February 2023 that vitamin D supplements are not effective for the treatment and prevention of either cancer or Covid-19.
Vitamin D should therefore only be supplemented when there are specific symptoms or a severe deficiency. A doctor’s prescription is also needed to buy medical products that contain vitamin D, because taken in excess it can be toxic. The Italian Medicines Agency states that vitamin D supplementation is recommended when the levels measured in a patient are below 12 ng/mL (30 nmol/L). Above these levels it is only recommended in the case of specific conditions, such as osteoporosis. People who do not suffer from any particular disorder just need to spend a bit more time in the open air, without having to monitor their vitamin D levels by means of repeated blood tests.
The Italian Medicines Agency has also provided guidelines on when a doctor may recommend taking vitamin D and the cases in which it is not appropriate.
A persistent sense of weakness, widespread or local muscle pain, falling frequently for no reason are all signs of vitamin deficiencies (hypovitaminosis), especially vitamin D. Anyone suffering from these symptoms is advised to consult a doctor and consider taking a blood test to measure their vitamin D levels. Taking supplements is only recommended if levels are below 12 ng/mL (or 30 nmol/L) even without symptoms, and a doctor’s prescription is always necessary.
Patients being treated with antiepileptic drugs, glucocorticoids and other medicines that interfere with vitamin D metabolism, or adults who suffer from diseases that interfere with absorption, such as Chron’s disease or cystic fibrosis, should take supplements if vitamin D levels are below 20 ng/mL (or 50 nmol/L).
In the case of osteoporosis or hyperparathyroidism, vitamin D supplements are required when levels fall below 30 ng/mL (or 75 nmol/L).
A prescription still needed, but the administration of supplements doesn’t take vitamin D levels into consideration for people who are institutionalised, those suffering from severe motor impairment or who are bedridden, women who are pregnant or breastfeeding, and those who have osteoporosis but cannot undergo treatment involving mineralisation.
Although the results of early epidemiological studies suggested that vitamin D could protect against cancer, more recent research has not confirmed this.
The European Prospective Investigation into Cancer and Nutrition (EPIC) was among the first studies to demonstrate that people with higher levels of vitamin D in their blood run a roughly 40 percent lower risk of colon cancer than those who have low levels of it. However, these results obtained in the laboratory have not been fully confirmed in clinical trials, i.e., studies involving patients.
According to the findings of various studies, such as the US Women’s Health Initiative that studied some 36,000 women for an average of seven years, taking vitamin D supplements does not seem to produce any protective effects. It can therefore be assumed that high levels of this vitamin in the blood are not directly responsible for the lower risk of cancer, they simply reflect healthier habits that are credited with protecting individuals from this disease.
Even the most recent research has not found vitamin D to have clear anti-cancer effects. No reduction in mortality or reduced likelihood of developing cancer was observed in those who took vitamin D supplements compared to those who did not.
The same is true for Covid-19. The data collected so far are not robust enough to be able to state that vitamin D can protect against severe forms of Sars-CoV-2 or other respiratory infections.