Vitamin D

What is vitamin D and how do you measure it?

Vitamin D is not an ordinary vitamin. Your body produces it largely on its own through the skin as soon as sunlight hits it. Only then does the body process this substance step-by-step into the active form that cells can use. The blood test measures the form known as 25-hydroxy-vitamin D, also called calcifediol. This is the best measure of the total amount of vitamin D present in your body.

After production in the skin, vitamin D travels to the liver, where it is converted into calcifediol. Subsequently, the kidneys convert this into calcitriol, the biologically active form. It is calcitriol that actually has an effect on bones, muscles, and the immune system. By measuring 25-hydroxyvitamin D, you get a reliable picture of your total vitamin D status, regardless of whether that vitamin D was obtained from the sun, food, or supplements.

Vitamin D is also found in a handful of foods, such as fatty fish, beef liver, and egg yolk. However, the amounts are limited. For most adults, the recommended daily intake is between ten and twenty micrograms, and for many people, extra supplementation is necessary to meet that need.

Why have vitamin D measured?

A vitamin D measurement can be useful for various reasons. In the case of vague complaints such as persistent fatigue, muscle pain, or recurring infections, it is wise to check the vitamin D level. Vitamin D deficiency often causes few specific symptoms, making it easy to overlook.

People at increased risk of deficiency benefit even more from periodic checks. This applies, for example, to people who spend little time outdoors, elderly people with reduced skin production, people with dark skin, overweight individuals, and people with intestinal disorders such as Crohn's disease or celiac disease. With these conditions, the absorption of vitamin D from food and supplements may be reduced, causing blood levels to remain low unnoticed.

Are you taking vitamin D supplements on the advice of a doctor? Then a blood test helps assess whether the dosage is sufficient. This prevents both a persistent deficiency and unwanted accumulation.

What do values ​​that are too low or too high mean?

A vitamin D level that is too low is the most common abnormality. With a deficiency, the body cannot absorb enough calcium from food, which eventually affects bone strength. In children, a severe deficiency can lead to rickets, a condition in which the bones become soft and deformed. In adults, a long-term deficiency increases the risk of osteoporosis, in which bones become porous and brittle.

In addition to bone problems, low vitamin D levels can be associated with loss of muscle strength, increased susceptibility to infections, and symptoms such as fatigue, concentration problems, and a depressed mood. Research also suggests a possible link to cognitive decline in the elderly, although this connection is still being investigated.

Excessively high vitamin D levels are less common and are almost never caused by sunlight alone. It is more likely to occur with long-term use of high doses of supplements. Too much vitamin D can lead to an excess of calcium in the blood, which can cause symptoms. If a value is unexpectedly high, it is advisable to contact a doctor to determine the cause.

Which factors influence your vitamin D level?

Vitamin D is particularly sensitive to lifestyle and environmental factors. In the Netherlands, the sun is too weak during the winter months to produce sufficient vitamin D in the skin. Those who spend little time outdoors or consistently use sunscreen run a greater risk of having lower levels, even outside of winter.

The skin plays a direct role in production. People with darker skin tones have more melanin, a pigment that absorbs ultraviolet light. As a result, vitamin D production is slower. Aging skin is also less efficient at converting sunlight into vitamin D, causing older people to develop a deficiency more frequently.

Vitamin D is stored in fatty tissue. In overweight individuals, vitamin D is, as it were, diluted over a larger mass of fat, which can contribute to lower blood levels. Furthermore, liver disorders can disrupt the conversion of vitamin D, and kidney disorders its activation. All these factors combined make it clear that vitamin D status is not the same for everyone and that a blood test is the most reliable way to assess your personal situation.