Vitamin D deficiency, what consequences it causes

By Cristiano Antonino Last updated May 19, 2023

It is called vitamin D, but we cannot consider it a vitamin in the strict sense. The term vitamin, in fact, identifies organic substances that are indispensable for life and that must necessarily be introduced through the diet as the body is unable to synthesise them

Vitamin D, on the other hand, is mainly synthesised through exposure to the sun’s rays, and under normal conditions it is not necessary to ingest it through food in order to reach an adequate concentration.

Vitamin D is more correctly a pre-hormone, which has the main task of regulating calcium and phosphorous metabolism

Dietary intake provides only 10-15% of the vitamin D requirement, while most is synthesised by the body through skin synthesis.

Vitamin D is found in two forms: vitamin D2, or ergocalciferol, of plant origin, and vitamin D3, or cholecalciferol, which is derived from cholesterol and produced directly by the body.

Being a pre-hormone, vitamin D must be activated by two hydroxylations, i.e. by two enzymatic reactions: the first occurs in the liver, the second in the kidney.

What vitamin D is used for

Vitamin D is a key component in the regulation of calcium and phosphorous metabolism: it promotes their absorption in the intestines and reduces their excretion in the urine.

It also acts directly on the skeleton, promoting its physiological growth and aiding its continuous remodelling, which is essential to ensure the structural properties, elasticity and strength of bone.

It is important that there is an adequate concentration of calcium in the blood, as a chronic deficiency can lead to a defect in bone mineralisation leading to the development of rickets in children and osteomalacia in adults.

Rickets is a particularly serious condition as it affects developing bones that have not yet reached peak mass and involves reduced growth associated with a pattern of specific skeletal deformities, particularly in the limbs.

Osteomalacia, on the other hand, affects an already mature bone and therefore mainly involves the weakening of the skeleton, which becomes more fragile and susceptible to fractures.

Although these conditions are still common in many developing countries, they are fortunately increasingly rare in industrialised countries, mostly presenting in a mild form and only exceptionally involving bone deformities.

In recent years, moreover, several studies have shown that vitamin D, in addition to playing a key role in maintaining skeletal health, is involved in a large number of extra-skeletal physiological functions.

The discovery of the presence of vitamin D receptors in many of the body’s cells and tissues has led to the hypothesis of possible pleiotropic functions, i.e. in the central nervous, cardiovascular and immune systems, as well as in cell differentiation and growth.

Some lines of research had suggested a possible association between vitamin D homeostasis and infectious, metabolic, tumour, cardiovascular and immunological diseases.

However, in spite of the large number of studies produced, it is important to emphasise that as yet there is no conclusive data on the protective role of vitamin D and therefore no solid and incontrovertible basis for recommending its use in these areas.

Vitamin D deficiency – what to do?

Unfortunately, in the case of a deficiency, there is no overt symptomatology; therefore, the diagnosis is mainly made by means of blood tests.

Normally, adequate vitamin D values are between 30 and 100 ng/ml: a value between 20 and 30 is therefore considered insufficient, deficiency a value below 20 and severe deficiency for values below 10.

Conversely, if the 100 ng/ml threshold is exceeded, an excess of vitamin D occurs, which can also lead to intoxication.

However, this is a very rare condition, which can in no way occur as a result of constant exposure to sunlight, whereas it can be caused by incorrect use of supplements.

For this reason, anyone with a vitamin D deficiency should follow the instructions of a specialist or general practitioner and avoid taking supplements on their own.

As a rule, it is preferable for the patient to take daily, weekly or monthly vitamin D supplements, which, under normal conditions, are taken orally.

The preferred form is the inactive form, i.e. cholecalciferol, the same form that is synthesised by the body through sun exposure.

Only in special conditions, such as malabsorption, is intramuscular administration preferred.

It is important to bear in mind that we must wait at least 3-4 months before the results of vitamin D supplementation are confirmed by blood tests.

How to take vitamin D

In our latitudes, in order to maintain an adequate level of vitamin D, exposure to sunlight of about 25% of the body surface, for at least 15 minutes 2-3 times a week, is sufficient from March to November.

In the remaining months, on the other hand, the intensity of sunlight is insufficient to convert the precursor into vitamin D, which is why sun exposure may not be sufficient.

During this period, certain groups should check their vitamin D levels and consider taking supplements with their doctor.

In addition, although their intake is not decisive, one can also resort to dietary sources rich in vitamin D, including fatty fish such as salmon, tuna or mackerel, egg yolk, bran and cod liver oil.

Vitamin D deficiency: who is most at risk?

The groups most at risk of deficiency are the elderly (in whom the skin’s capacity for synthesis is reduced), institutionalised individuals or those with inadequate sun exposure, people with dark skin (who, therefore, have more skin pigment, which reduces the absorption of ultraviolet rays), pregnant or lactating women, people suffering from obesity and those who have extensive dermatological pathologies, such as

vitiligo
psoriasis
atopic dermatitis
burns

Also at risk are patients with intestinal diseases that cause malabsorption, those suffering from osteoporosis or osteopenia, those with kidney and liver disease, and those taking drugs that interfere with vitamin D metabolism, such as chronic corticosteroid or anti-corticosteroid therapies.

These categories of patients should periodically check their vitamin D levels and, in case of deficiency, agree on a course of supplementation.

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