Why can vitamin D levels remain low after a sunny summer?

The summer was full of sun this year, but vitamin D deficiency is diagnosed among Estonian people regardless of the weather. Dr Irina Utenko, laboratory doctor at SYNLAB, advises on what affects the absorption of vitamin D and the right time to check the storages obtained over the summer in your body.

"There is certainly hope that we received sufficient vitamin D in the summer, but our daily tests show that the vitamin reserves of Estonian people still need to be replenished," says Dr Irina Utenko, laboratory doctor at SYNLAB.

According to her, it is recommended to evaluate the vitamin D reserves collected in the summer in your body at the end of September, beginning of October, or two or three weeks after returning from a trip to the sun. The sun is not enough if the body has an increased need for vitamin D. It is also good to keep in mind the reasons that can prevent vitamin absorption.

Higher vitamin D need: pregnancy, breastfeeding and sports

According to Dr Utenko, the need for vitamin D is higher in pregnant women and breastfeeding mothers, who should regularly take more vitamin D to cover the body’s increased need. According to a study by the University of Tartu "Serum level of vitamin D in the second pregnancy trimester has an impact on pregnancy outcome and maternal health", low levels of vitamin D are common among pregnant Estonian women, and its main risk factors include pregnancy during calendar months with low solar intensity as well as pre-pregnancy obesity. The level of vitamin D in the body affects the course of pregnancy and the health indicators of the mother and child. Research shows that the reserves of vitamin D stored in Estonia during the summer months are not sufficient for our future mothers to cover the winter period.

According to Dr Utenko, there could be a higher supply of vitamin D in people who regularly do heavy sports so that the body can better cope with stress.

Weaker synthesis of vitamin D in the skin when exposed to the sun

As a person ages, the skin no longer synthesises vitamin D as efficiently as before and it becomes easy to develop a deficiency. Melanin reduces the ability of the skin to synthesise vitamin D, and this is why synthesis in the skin is weaker not only in the elderly, but also in people with darker skin, and it is worth checking your reserves.

The causes of vitamin D deficiency after a hot summer are sometimes very mundane and related to our lifestyle. According to Dr Utenko, the healthiest time to be in the sun would be between 09:00 and 12:00 in the morning. But how many of us actually spend time outdoors at this time, especially on weekdays? In addition, the synthesis of vitamin D in the skin can be affected by cloudy weather, air pollution or the use of creams with a sun protection factor (higher than SPF8).

The causes of deficiency may be related to the general state of health of the person.

Absorption is difficult in the event of diseases of the small intestine, such as celiac disease or inflammatory bowel disease, after gastric bypass surgery or when taking some medications. Vitamin D deficiency is also common with chronic alcoholism.

Vitamin D is a fat-soluble vitamin absorbed throughout the small intestine, while the reserve is stored in liver tissue and adipose tissue. "Therefore, an overweight person has a large reserve of vitamin D, but the body cannot easily get it from fat tissue. If a person loses weight, it is worth reviewing the doses of vitamin D, "explains Dr Utenko.

Diet has an important influence on absorption. Absorption is reduced by food that is too rich in fibre and excessive coffee consumption. Vegetarians also tend to have a deficiency.It should be noted that other fat-soluble vitamins, such as vitamins A, E and K, compete for dissolution in the small intestine and may also prevent the dissolution and absorption of vitamin D. Therefore, it is important to pay attention to your diet as a whole.

Apart from sunlight, people get vitamin D from food or as a supplement. The main rich sources of vitamin D are cooked fish (especially herring, salmon) and boiled eggs. Milk and milk products enriched with vitamin D are suitable. According to Dr Utenko, vitamin D obtained from food or taken as a preparation dissolves equally in the small intestine. However, since vitamin D is fat-soluble, it should be taken with a meal that contains more fat. Useful fats are, for example, chia seeds, avocado, milk fat, which ensure better absorption.

Why do we talk so much about vitamin D these days?

According to Dr Utenko, vitamin D used to be known more as a children’s vitamin. This is because only part of the useful properties were known – this vitamin is the one that keeps bones and teeth in order. Advances in science and new research have given vitamin D a much broader meaning in recent decades. Today, it is known that vitamin D regulates more than 200 genes, which is why this vitamin is important in many physiological processes in the human body.

"Vitamin D not only regulates the metabolism of calcium and phosphate to keep bones and teeth in good condition, but also affects the cells of the immune system and the synthesis of the insulin hormone in the pancreas, helps regulate blood pressure, blood clotting, nerve tissue function, helps keep muscles toned and improves performance. Today, a low level of vitamin D is associated with a higher risk of developing diabetes, tumours, various infections, etc.," explains Dr Utenko and adds that the effect of the vitamin in the prevention of seasonal colds cannot be underestimated. Recent research highlights the role of vitamin D in men’s health, as a deficiency can lead to low testosterone levels. Doctors help create connections with various health indicators based on tests.