Vitamin D and sunshine: benefits, precautions and what to do in winter

Vitamin D, of which the best-known forms are vitamin D2 and vitamin D3, refers to a series of compounds that can be minimally taken through diet and food supplementation, being synthesised in adequate quantities by the body through exposure to direct sunlight.

Vitamin D performs several useful functions for the wellbeing of the entire body: for example, it plays an important role in healthy bones and teeth, contributes to the intestinal absorption of calcium and phosphorus, and promotes the proper functioning of the immune and muscular systems. This explains why a vitamin D deficiency is related to disorders that can particularly undermine bone health.


Vitamin D is also called the ‘sunshine vitamin’ because it’s produced by the body when sunlight hits the skin directly.

At the latitude of Italy, 80% of vitamin D intake is provided by UVB exposure, with the remaining 20% generally provided by food.

How long should we expose ourselves to the sun to produce adequate amounts of vitamin D? The factors that influence the skin’s production of vitamin D are mainly UVB radiation and individual characteristics.

UVB ultraviolet rays of a specific wavelength are required for vitamin D synthesis to be activated. These radiations reach the atmosphere, and are therefore available to exposed skin, only for a limited number of hours, which varies according to season and latitude. In Italy, in the winter months the proportion of UVB responsible for vitamin D production decreases due to the increased angle of the sun’s rays with the earth. Solar radiation is also influenced by weather conditions (in particular the presence of clouds) and air pollution, which lead to an increase in the ozone layer, which can absorb UVB rays.

The synthesis of vitamin D also varies from person to person, depending on the state of pigmentation of the skin: those who have darker skin, therefore richer in melanin, are able to synthesise, with the same amount of sun exposure time, less vitamin D than those with lighter skin. Age can also influence its synthesis: the elderly, all things being equal, produce up to 30% less vitamin D than young people. In addition, creams with sunscreens, which are important and essential for protecting the skin during direct sun exposure, can reduce vitamin D production.

According to the Italian Society of Osteoporosis, Mineral Metabolism and Skeletal Diseases (SIOMMMS), it’s sufficient to expose the face, arms, legs or back to the sun for about 15-30 minutes, between 10 am and 3 pm, at least twice a week and without protection, to stock up on vitamin D and cover the body’s requirement. It’s important to remember that exposure must be direct, because UVB rays don’t pass through glass.

Direct sunlight helps produce vitamin D, but overexposure to solar radiation can cause acute and chronic adverse effects on the health of the skin, eyes and immune system.

Excessive exposure to the sun, in fact, in addition to promoting lesions such as redness and skin burns, can also contribute to premature skin ageing phenomena.

You therefore need to be cautious when spending time outdoors and exposing yourself to the sun properly, always following some simple precautions:

  • In summer, limit as much as possible direct exposure to the sun during the central hours of the day, between approximately 11 a.m. and 4 p.m. Even in the shade, ultraviolet rays can reach the skin, reflected by surrounding surfaces (water, sand) or passing through tissues
  • When exposure is unavoidable, it’s important to apply protective sun creams (with protection factors of at least +15 and in any case suitable for your phototype) with anti-UVA and UVB sun filters to skin not covered by clothing. In order to be useful and effective, these products must be used correctly, in the right quantities, repeating the application every two hours and even more often where there is intense sweating or after a bath or shower
  • Protect your eyes from the sun with appropriate glasses.

Particular attention should be paid to children and infants. Experts generally advise against direct sun exposure in the first year of life.

Normal exposure to sunlight from March to September is sufficient to provide the necessary amount of vitamin D in adults. This vitamin can be stored in the adipose tissue in large quantities, and be used by the body when needed.

Data from many studies has shown that vitamin D deficiency is quite frequent in Italy, especially in the elderly and during the winter months. Estimates suggest that 86% of women over the age of 70 have lower-than-normal vitamin D values at the end of winter, and the situation is particularly significant in all those people who cannot, for various reasons, spend time outdoors and thus synthesise vitamin D.

According to the LARN (reference intake levels for the Italian population) drawn up by SINU (the Italian Society of Human Nutrition), the daily requirement of vitamin D is 15 micrograms per day in adults, corresponding to 600 IU (international units).

In order to assess a possible vitamin D deficiency (for example during menopause), it’s advisable to contact your GP, who’ll be able to request vitamin D blood level tests and assess the possible need to take vitamin D supplements.


Based on the results collected and the examination, your doctor may suggest doses and timing of vitamin D supplementation.

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