Normal vitamin D level in the blood

Vitamin D, also called calciferol, is a fat-soluble vitamin essential for the normal development of bones and teeth.

Despite its name, vitamin D is not actually a vitamin but a hormone with several important roles in the body:

• It is required for the absorption of calcium and phosphorus by the intestinal tract (and magnesium to a lesser degree).
• It protects against muscle weakness
• It is involved in regulating heartbeat

Vitamin D is obtained in two ways:

• Endogenously: Produced by the skin when exposed to sunlight.
• Exogenously: Absorbed from foods and supplements..

Vitamin D is often called the "sunshine vitamin" because it is produced when the skin is exposed to sunlight.

There are two forms of vitamin D:

• Vitamin D3 (cholecalciferol): Obtained from animal sources and produced in the skin when exposed to ultraviolet sunlight.
• Vitamin D2 (ergocalciferol): Found in plants and yeasts.

Only a few foods contain significant amounts of vitamin D, including fish liver oils, fatty fish (such as sardines, mackerel, trout, and salmon), egg yolks, liver, and dairy products. Some foods, like cereals, are also fortified with vitamin D.

In the body, vitamin D is first metabolized in the liver to its main circulating form, 25-hydroxyvitamin D [25(OH)D], and then in the kidneys to its biologically active form, 1,25-dihydroxyvitamin D [1,25(OH)2D], which acts as a hormone regulating calcium and phosphate metabolism.

Taking a multivitamin with vitamin D can maintain better bone health. The recommended daily intake of vitamin D varies by age: 400 international units (IU) for infants up to 12 months, 600 IU for individuals aged 1 to 70 years, and 800 IU for those over 70.

A deficiency in vitamin D impairs bone formation, leading to rickets in children and osteomalacia in adults.

The vitamin D blood test typically measures the level of 25-hydroxy vitamin D [25(OH)D], which is the main circulating form of vitamin D in the blood. The 25(OH)D levels do not fluctuate much from day to day, even with changes in sunlight exposure or dietary intake, making this measurement relatively stable and easy to assess.

The vitamin D blood test is often requested in cases of:

• Bone problems or diseases (osteoporosis, bone fractures, etc.)
• Hypocalcemia (low calcium levels in the blood))
• Low or limited exposure to sunlight

High levels of vitamin D in the blood are uncommon and may be a sign of vitamin D toxicity, usually caused by excessive daily intake of high-dose vitamin D supplements.

Low levels of vitamin D in the blood may be due to insufficient dietary intake of vitamin D or inadequate sunlight exposure.

Each laboratory must establish its own normal ranges for vitamin D in the blood. These ranges depend on the makeup of the local population, the technologies used and the accuracy of the measurement. There may be also slight differences in the normal levels, according to age, gender, race or ethnic origin, geographic region, diet, type of sample and other relevant status.

Your doctor will study the results along with your medical record, screenings, physical condition, symptoms and any other relevant information about your situation.

Vitamin D levels depend on sunlight exposure. They show seasonal variation, with the highest concentrations typically in summer or fall and the lowest in winter or spring. Additionally, the body's production of vitamin D has been reported to decrease with age.

The values shown above refer to the 25-hydroxy vitamin D [25(OH)D] test which is the main circulating form of vitamin D in the blood. However, there is also a test to measure the 1,25-dihydroxyvitamin D [1,25(OH)2D] in the blood and the normal ranges for it are 15 to 60 pg/mL (36 to 144 pmol/L).

The following values are considered to be normal values:

IMPORTANT: These levels are expressed in ng/ml. They are an example of a healthy adult of about 45 years old with no known disease with an adequate sunlight exposure and not taking any medication. The ranges can be different depending on the laboratory or on your personal circumstances.