Vitamin D3, or cholecalciferol, is synthesized by the skin after exposure to sunlight and is added to many foods as a supplement. It interacts with approximately 2,000 genes in the human genome and is linked to diseases such as cancer, hypertension, and osteoporosis. Both deficiency and excess can cause disease, with deficiency leading to rickets and hypovitaminosis D, and excess leading to hypervitaminosis D.
Cholecalciferol, also called vitamin D3 or calciol, is a form of vitamin D and is synthesized by the skin after exposure to sunlight. This form of vitamin D is also added to many foods as a supplement, and is prescribed as a medication for people who are unable to maintain adequate levels of vitamin D. Although called a vitamin, cholecalciferol is technically a steroidal dry hormone, and is structurally similar to hormones like testosterone and cholesterol.
In terms of its importance in the human body, vitamin D is virtually unmatched. The metabolic product of this vitamin, called calcitriol, is known to interact with approximately 2,000 of the 20,000 genes in the human genome. Vitamin D deficiency has been correlated with more than a dozen cancers, as well as other serious diseases such as high blood pressure, type 2 diabetes, stroke, and heart disease.
In the presence of ultraviolet B sunlight, cholecalciferol forms from a precursor molecule called 7-dehydrocholesterol. In the liver, cholecalciferol is metabolized to calcifediol, which is further modified in the kidneys to become calcitriol. The conversion of 7-dehydrocholesterol to calcitriol is regulated by several mechanisms. For example, the conversion of calcifediol to calcitriol in the kidneys is regulated by parathyroid hormones secreted by the parathyroid glands.
With the exception of supplemented foods, vitamin D can be obtained from very few foods. The richest natural sources of vitamin D include fish oils, fatty fish such as salmon, catfish, tuna, eggs, and beef liver. Doctors often recommend supplements or fortified foods for people who don’t get the recommended minimum of vitamin D each day. The recommended minimum is generally between 200 and 600 international units per day, depending on the age of the individual.
Both deficiency and excess of cholecalciferol or other forms of vitamin D can cause disease. Vitamin D deficiency, also known as hypovitaminosis D, can cause a childhood disease called rickets, which leads to malformed development of long bones such as those in the legs. This disease is rare in countries where milk is fortified with vitamin D. Hypovitaminosis D is a major risk factor for osteoporosis and is linked to chronic diseases such as hypertension, autoimmune diseases, and various types of cancer.
An excess of vitamin D is called hypervitaminosis D. Symptoms include nausea, vomiting, constipation, loss of appetite, increased thirst, dehydration, fatigue, and nervousness. Severe toxicity can lead to kidney failure and heart disease due to high levels of calcium in the blood, but this toxicity can be effectively treated with a low-calcium diet and steroid medications. It is extremely rare for vitamin D toxicity to occur as a result of dietary modifications or supplement use. Almost all cases of vitamin D toxicity have resulted from industrial accidents that have led consumers to buy fortified foods or supplements that contain extremely high levels of the vitamin.
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