Low levels of vitamin D are a problem for many people today. Deficiency in this vitamin is associated with the development of certain chronic diseases and metabolic disorders. In recent years, several studies have been conducted to rediscover the various benefits of vitamin D intake. However, deficiency in the “sunshine vitamin” is extremely common on a global scale.
The recommended daily dose for optimal vitamin D intake in 2010 was 600 International Units (I.U.) for children and adults, and 800 I.U. for individuals over 70 years old. However, recent scientific studies are not unanimous regarding the recommended dosage. It varies depending on age, gender, and the person’s health condition. Some studies suggest higher doses of vitamin D, especially for groups at increased risk of deficiency. For example, the American Society of Endocrinology recommends a daily intake of 600 to 2000 International Units (I.U.) depending on age and risk factors. Other studies also suggest higher doses ranging from 1000 to 4000 I.U. per day. Despite the increase in the recommended dose, many experts believe it is still too low to maintain adequate levels of vitamin D in the blood.
Metabolism of Vitamin D
Vitamin D is naturally produced by keratinocytes in the epidermis of the skin when exposed to ultraviolet light from the sun. Small amounts can also be found in certain foods such as fatty fish, free-range egg yolks, liver, and some dairy products.
Vitamin D exists in two different forms: vitamin D2 (ergocalciferol) and D3 (cholecalciferol). The skin produces D3, and it is naturally present in animal-based foods. Vitamin D2 is found in some plants but is usually produced in the form of dietary supplements by processing yeast. Typically, vitamin D3 is of animal origin, while vitamin D2 is derived from yeast. Lichens, however, are a plant source of vitamin D3 – a very rare occurrence in the plant kingdom.
Despite the availability of dietary sources of vitamin D, it is sometimes practically impossible to maintain optimal levels of this vitamin through diet alone. For people living in specific geographical latitudes (located in the north), it may also be challenging to maintain adequate vitamin D levels. That is why dietary supplements are a means of maintaining adequate vitamin D levels throughout the year.
Difference between Vitamin D2 and D3 Supplements
The difference between vitamin D2 and D3 supplements is important when it comes to their effects on vitamin D metabolites in the blood. Interestingly, long-term intake of vitamin D3 proves to be more effective than vitamin D2 intake. However, health authorities usually do not make a clear distinction between the two forms of the vitamin in their recommendations.
Vitamin D3 is the form that most closely resembles the vitamin naturally produced in our bodies when exposed to sunlight. It is considered more biologically active and more readily absorbed by the body. On the other hand, vitamin D2 is found in some plants and can be produced synthetically. While both vitamins can increase vitamin D levels in the blood, numerous studies show that vitamin D3 has stronger effects and better bioavailability.
Deficiency of vitamin D
Vitamin D plays an important role in human health and the optimal functioning of various organs and systems in the body. Insufficient intake of vitamin D can lead to various diseases.
One of the most common problems associated with this deficiency is osteoporosis. Vitamin D is necessary for the adequate absorption of calcium from the bones, which helps maintain their strength and density. Insufficient amounts of the vitamin can lead to reduced bone mineralization and an increased risk of bone fractures.
Vitamin D deficiency is also associated with immune system disorders. It plays a crucial role in regulating the immune response and has anti-inflammatory properties. Insufficient levels of vitamin D in the blood can predispose individuals to inflammatory conditions such as rheumatoid arthritis and inflammatory skin diseases.
Deficiency is also linked to heart and cardiovascular diseases. Studies show that low levels of vitamin D are associated with an increased risk of developing hypertension, coronary artery disease, and cardiovascular events such as myocardial infarction and stroke.
Some of the diseases associated with vitamin D deficiency include:
- Osteoporosis and bone fractures.
- Immune system disorders, including rheumatoid arthritis and inflammatory skin diseases.
- Hypertension and cardiovascular diseases.
- Cancer, such as breast cancer, colorectal cancer, and colon cancer.
- Type 2 diabetes and metabolic syndrome.
- Depression and mental disorders.
- Upper respiratory tract infections and respiratory diseases.
- Autoimmune diseases like systemic lupus erythematosus and scleroderma.
- Impaired muscle function and weakness.
- Fertility problems and delayed growth in children.
Function of vitamin D
In our bodies, vitamin D3 and D2 are converted to 25-hydroxy vitamin D [25(OH)D] in the liver. This chemical substance is then transformed into the biologically active form of vitamin D, called calcitriol, by the kidneys.
Calcitriol has several important functions in the body. It acts on the small intestine to enhance calcium absorption and regulate serum calcium and phosphorus levels. These actions are linked to the influence of vitamin D on calcium balance. Interestingly, its influence is not limited to calcium metabolism alone.
Accurate measurement of vitamin D is important as numerous studies associate low levels of vitamin D with an increased risk of various diseases. New research continues to discover a wide range of potential benefits of vitamin D for the cardiovascular system, immune system, cognitive functions, and brain health. These diverse functions in the body can be explained by the mechanisms through which vitamin D operates.
Calcitriol, the active form of vitamin D, not only acts as a classical hormone but also exhibits characteristics of a steroid hormone. It binds to receptors on cell membranes and nuclei known as vitamin D receptors (VDR). This process stimulates gene transcription in various types of tissues. Interestingly, more than 50 genes are regulated by vitamin D, although the majority of them are not related to calcium metabolism.Vitamin D receptors are found in the gastrointestinal tract, brain, breasts, nervous system, and various tissues, including those not associated with bones. Calcitriol plays an important role in the immune system, cell differentiation and proliferation in the skin, muscles, pancreas, nervous system, and parathyroid gland. Additionally, vitamin D reduces inflammation and improves cellular insulin sensitivity.