Vitamin D and Sun: Vital Balance

Detection of Low Vitamin D Levels: A Growing Reality

The detection of low levels of vitamin D is increasingly common in our population. The causes of this deficiency are not completely clear, which generates controversy between the recommendation of rigorous sun protection and the reduction in vitamin D synthesis that this may entail. In this article, we break down the most important aspects of this relationship to clarify relevant doubts for both our patients in the dermatology consultation and in the pharmacy office.

Introduction to Vitamin D

Vitamin D is a fat-soluble vitamin that acts through intracellular receptors, activating the synthesis of proteins involved in the absorption of calcium. It occurs in different forms in the body, with 25-hydroxyvitamin D being the majority circulating form, and 1,25-dihydroxyvitamin D being the active form, which is activated in the kidney. Vitamin D is present in few foods such as fatty fish (e.g. salmon) and fortified foods (cereals, milk). The primary source of vitamin D is cutaneous synthesis, where the dermis produces provitamin D3 from 7-dehydrocholesterol during exposure to ultraviolet (UV) radiation from the sun, which is then converted to 25-hydroxyvitamin D in the liver.

Desirable serum levels of 25-hydroxyvitamin D are not clearly established. The National Academy of Medicine in the United States considers that levels higher than 20 ng/mL are sufficient, while other associations focused on osteoporosis and endocrinology recommend levels higher than 30 ng/mL for adequate bone metabolism.

Implications of Vitamin D Deficiency

In addition to its role in bone metabolism, vitamin D deficiency can affect other organs and systems. This is because the vitamin D receptor is expressed in all nucleated cells, giving it endocrine and paracrine functions. It has been noted that low levels of vitamin D may increase the risk of cardiovascular disease, certain cancers (e.g., colon cancer), autoimmune diseases (e.g., multiple sclerosis), and pregnancy complications.

Vitamin D and UV Radiation

The synthesis of provitamin D in the skin occurs thanks to the sun's UVB rays, which can cause mutations in the DNA of skin cells, initiating carcinogenic processes. Sunscreens, especially those with SPF 50+, block more than 98% of UVB radiation. People who spend a lot of time indoors (e.g., elderly people in nursing homes, prisoners) or who live at high latitudes have deficient levels of vitamin D. This raises the question of whether the rigorous use of sunscreens can cause a vitamin D deficiency. However, studies show that, even using photoprotectors, there is always a small percentage of UVB radiation that reaches the skin, sufficient for the synthesis of vitamin D.

Vitamin D and Sun Protection

Fortunately, the skin system for vitamin D synthesis is highly efficient. Studies in Spain indicate that exposing 25% of the skin for 3-8 minutes in summer is sufficient to satisfy the physiological needs of vitamin D. Studies have not shown that sunscreens cause a significant reduction in vitamin D levels. This This is because, even with the best sunscreen, 2% of UVB radiation penetrates and promotes cutaneous synthesis of vitamin D. Furthermore, suboptimal application of sunscreen by most people leaves room for some UVB to reach the fur.

Rigorously avoiding the sun through protective clothing, hats, or staying indoors can reduce vitamin D levels, but using sunscreen creams if you spend time outdoors does not. If low levels of vitamin D are detected, oral supplementation is an effective solution.

Conclusion

Vitamin D is essential for the proper functioning of the body. A proper diet and outdoor living can provide sufficient levels of this vitamin. The use of sunscreen is not directly related to low levels of vitamin D in the population that uses it. It is crucial to maintain the recommendation of photoprotection to prevent skin cancer, assuring patients that it will not be the cause of their low vitamin D levels. In case of deficiency, oral supplementation is the best option.

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