Vitamin D is a fat-soluble vitamin essential for good health. Two primary types of vitamin D exist. Vitamin D2 is plant-synthesized ergosterol, a steroid, converted into a vitamin by ultraviolet light. Vitamin D3 is generated by the skin or consumed in food or supplements. Vitamin D3 provides the most biologically available benefits for humans. According to Dr. John Whitcomb, physician at Aurora Sinai Medical Center, vitamin D3 is the number one public health advance in medicine in the last 20 years.
Biochemistry
Vitamin D3 is synthesized in the skin when exposed to ultraviolet-B rays from sunlight. Vitamin D3 is produced endogenously by the body, meaning there is no dietary requirement for this vitamin. Fifteen minutes of direct sunlight daily can produce enough vitamin D to sustain good health, according to Harvard School Public Health. However, individuals with dark skin have more difficulty producing vitamin D3 in the skin and possess lower vitamin D3 levels. Vitamin D3 acts similar to a hormone in that it is biologically inactive until metabolized. Once vitamin D3 enters the body, it is transported to the liver and then to the kidneys before activation. From there, it travels to the nucleus of cells, where it begins functioning biologically.
Nutrition
Individuals can also obtain vitamin D3 through dietary sources, although few foods are naturally rich in vitamin D3. Those foods are salmon, tuna, herring, mackerel and sardines. Some foods are fortified with vitamin D3, such as dairy foods and cereals. Due to the difficulty of getting adequate amounts of vitamin D3 from your diet, the Harvard School of Public health recommends everyone take a vitamin supplement. The National Institutes of Health recommends everyone from ages 1 to 70 consume at least 600 IU of vitamin D3 daily and those older than 70 consume 800 IU daily.
Function
Vitamin D3 primarily functions to sustain normal blood levels of phosphorus and calcium. Vitamin D3 assists in the absorption of calcium, aiding in the formation and maintenance of healthy bone. According to MayoClinic.com, vitamin D3 protects against osteoporosis, high blood pressure and some autoimmune diseases. Additionally, an association between colorectal cancer and low vitamin D3 levels has been established, according to Harvard School of Public Health. Osteomalacia and rickets are disorders associated with vitamin D3 deficiency. In children, rickets leads to skeletal deformities. Among adults, osteomalacia leads to muscular weakness and brittle bones.
Warnings
Vitamin D3 is generally a very safe vitamin and difficult to acquire toxic levels. However, doses greater than 50,000 IU per day may cause hypercalcemia, a disorder with toxic levels of calcium in the blood, and nephrocalcinosis, a decrease in renal function. The National Institutes of Health set the maximum daily intake of vitamin D3 at 4,000 IU. If you are consuming more than the aforementioned amount, monthly blood tests to monitor calcium serum and thyroid hormone levels should be conducted to protect against vitamin D3 toxicity.
References
- MayoClinic.com: Vitamin D
- Harvard School of Public Health: The Nutrition Source: Vitamin D and Health
- Linus Pauling Institute at Oregon State University; Micronutrient Information Center: Vitamin D
- Vitamin D Council: Vitamin D Quotes
- Office of Dietary Supplements: National Institutes of Health; Dietary Supplement Fact Sheet: Vitamin D
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