Dry Eye: Why Does It Get Worse in Winter?

Vitamin D is a fat-soluble molecule that forms in our skin through the action of sunlight. Indeed, when the sun hits our skin, it induces a photolysis reaction that converts a cholesterol precursor into the inactive form of Vitamin D (previtamin D3). This previtamin is then subsequently metabolized and activated.

The importance of Vitamin D is now widely documented by scientific literature, and it represents a crucial vitamin for our body's well-being. The biological action of this vitamin is evident on bone tissue, where the molecule regulates calcium levels, and on the pancreas, where it regulates the normal secretion of insulin and simultaneously promotes calcium reabsorption in the kidneys. It also plays an important role in mammary glands, salivary glands, and the thyroid gland. Vitamin D's role also gains importance in the immune system, where it reduces the synthesis of inflammatory mediators. For this reason, a Vitamin D deficiency is often at the root of autoimmune diseases.

Vitamin D contributes to the well-being of not only structures like the intestines, bones, and kidneys, but also our eyes. Many structures on the ocular surface have receptors, specialized proteins present on our cells, to which the vitamin binds to perform its biological functions. The basal production of estrogen hormones is also strongly regulated by Vitamin D. The same Vitamin D-sensitive receptors present on the conjunctiva and Meibomian glands are also sensitive to fluctuations in hormone levels that are found especially in females during the menopausal period. Consequently, low levels of Vitamin D in the body are reflected on the ocular surface through the appearance of symptoms attributable to dry eye. Vitamin D also shows reparative effects in improving the junctions between cells, strengthening the cell-to-cell barrier while stimulating the production of specific proteins (cathelicidins D) that induce the healing of inflammatory processes. A recent scientific study confirms how Vitamin D on the ocular surface can decrease inflammatory mediators. Dry eye is a multifactorial condition because it depends on a variety of environmental factors, lifestyles, and predisposing health conditions. A characteristic of Dry Eye is the presence of an inflammatory state on the ocular surface caused by a tear film imbalance. Here, the action of Vitamin D plays an important role, allowing for the decrease of inflammatory cells through the same mechanisms involved in immune conditions (rheumatoid arthritis). Inflammation of the ocular surface, in fact, is often the first sign that leads to tear evaporation from the cornea, leaving the eyes dry. Therefore, one feels ocular burning and a foreign body sensation.

Vitamin D levels in our body physiologically tend to decrease during the autumn and winter period due to less exposure to sunlight. It's possible to replenish it through diet and by taking Vitamin D supplements.

Vitamin D synthesis is largely influenced by age, health conditions, exposure to sunlight, and lastly, but not least importantly, by diet. Following a balanced diet is fundamental for the prevention of many systemic pathologies. In particular, a proper Mediterranean diet allows for the intake, in appropriate doses, of a correct variety of nutrients such as vitamins, minerals, fibers, proteins, and carbohydrates, which should be differentiated, avoiding saturated fatty acids and refined flours as much as possible. Specifically, some foods, more than others, have a higher quantity of Vitamin D. In particular, with the intention of increasing the intake of foods with a high quantity of Vitamin D, it is appropriate to consume foods such as:

• Fish, especially herring, tuna, mackerel, salmon, swordfish, trout.

• Eggs, though Vitamin D is present in very low percentages.

• Cod liver oil, which is particularly rich in Vitamin D.

• Dairy products (yogurt) and cheeses.

• Dried mushrooms.

• Dark and large-leaf vegetables (broccoli, kale).

• Cocoa. 

It's always advisable to prefer light cooking to avoid the dispersion of important nutrients.

In cases where significant Vitamin D deficiencies manifest, it's advisable to consult your doctor and evaluate the intake of a Vitamin D supplement.

In the presence of dry eye symptoms, it's a good habit to use artificial tears. They represent a valid aid to counter the first signs of dry eye, to restore an insufficient tear film, or when the latter is not well-balanced.