For elderly people and patients with osteoporosis, the recommendation is to extend this to 30 minutes.

In both cases, sunblock with an SPF between 15 and 30 should be used, depending on the latitude and intensity of UV (ultraviolet) radiation.

Dietary intake is also necessary.

Good dietary sources of vitamin D include oily fish (especially salmon and trout), full-fat dairy products, margarines and fortified vegetable drinks.

Some common health choices may be behind the growing vitamin D deficiency.

These include the increasingly frequent use of sunscreen and the reduced consumption of fatty foods.

Supplements: when should we take them? Currently, vitamin D levels are assessed by determining the serum concentration of 25(OH)D, though results can vary depending on the analytical method used.

In general, values above 20 nanograms per millilitre (ng/mL) are considered optimal for the general population.

They should be above 30 ng/mL for people over 65 years of age, patients with bone conditions, or those undergoing chronic drug treatments such as corticosteroids or anticonvulsants.

Values between 12 and 20 ng/mL are considered insufficient, and anything below 12 ng/mL is considered a deficiency.

There is also concern about the risks of too much vitamin D, known as hypervitaminosis D, which occurs at 25(OH)D levels above 100 ng/mL.

For people with adequate 25(OH)D serum levels, there is debate over whether vitamin D supplements should be prescribed in order to improve their immune response.

To address this question, a 2022 meta-analysis evaluated the effects of supplements of 1,000-2,000 international units (IU) per day in healthy individuals.

The analysis concluded that the supplements did not lead to significant improvements in immune system function, nor did they help prevent illnesses such as acute respiratory diseases, influenza, or COVID-19 infection.

However, other authors have observed positive effects of this intervention in individuals with respiratory diseases, especially in those with vitamin D deficiency.

There are also conflicting results regarding its benefits in patients with metabolic diseases and neurodegenerative conditions.

Too much vitamin D? The intake of vitamin D from food is unlikely to cause problems.

However, indiscriminate use of supplements in people who are not deficient can lead to chronic toxicity.

For example, the administration of vitamin D supplements in doses exceeding 4,000 IU/day for prolonged periods can raise serum 25 (OH)D concentrations to values above 50 ng/ml.

This leads to a risk of excessive levels in the body, known as hypervitaminosis.

The most common manifestation of hypervitaminosis D is hypercalcaemia.

This is characterised by gastrointestinal symptoms (anorexia, nausea, vomiting and constipation) alongside weakness and fatigue.

In the most severe cases, it can cause polyuria (excessive urine production), polydipsia (abnormal increase in thirst), renal failure, ectopic calcifications (outside the normal areas), depression, confusion, bone pain, fractures, and kidney stones.

Due to increased consumption of supplements, cases of toxicity have risen significantly in recent years.