Vitamin D is a fat-soluble vitamin essential for numerous processes in the body. Vitamin D participates in and regulates the metabolism, allowing it to function properly. Among many other functions, vitamin D is responsible for the regulation of bone development, muscle function, optimum immune function, insulin activity, calcium balance and phosphorus balance. Vitamin D comes in two elemental types: ergosterol, the basic building block of vitamin D in plants, and cholesterol - the basic building block of vitamin D in humans. When ultraviolet light from the sun hits the leaf of a plant, ergosterol is converted into ergocalcifero. In the same way, when ultraviolet light hits the surface of the human skin, one form of cholesterol found in the skin cells converts into cholecalciferol, a form of vitamin D.
Causes of low vitamin D levels
One of the most significant causes of low levels of vitamin D is insufficient sun exposure. However, the simple sunlight is not all that it takes to get sufficient levels of vitamin D from the cholesterol. Conversion of cholesterol to vitamin D is possible only if the UVB light is present. The intensity of this light varies with geographical location, time of the year, time of day, degree of cloud cover and other factors.
Skin pigmentation is another important factor in synthesis of vitamin D. People with darker skin will receive less vitamin D synthesis per minute exposure to UVB light.
Under optimal circumstances, human skin can synthesize between 10,000-20,000 IU of vitamin D in 30 minutes of sun exposure. Spending a lot of time outdoors in the sun increases one's chances of getting enough vitamin D. In correlation, spending a lot of time indoors, in the office, or wearing protective clothes and sunscreens, drastically decreases synthesis of vitamin D.
Pregnant and lactating women may also have low levels of vitamin D, as they must supply their infants with sufficient amounts.
Insufficient dietary fat or inability to absorb dietary fat, may also interfere with vitamin D levels. Vitamin D is fat-soluble vitamin and diet lacking in fats may reduce synthesis of vitamin D and overall vitamin D levels in the body.
Diseases that affect the parathyroid gland, liver and kidneys may weaken the synthesis of the active form of vitamin D.
Age is also an important factor for vitamin D synthesis as the production of vitamin D precursors in the skin decreases with age.
Public Health Recommendations
The adequate intake levels for vitamin D are: Infants and children: 5 micrograms (200 IU) Teenagers: 5 micrograms (200 IU) Adults up to 50 years of age: 5 micrograms (200 IU) Adults 51-70 years: 10 micrograms (400 IU) Adults above 70 years: 15 micrograms (600 IU) Pregnant and lactating women: 5 micrograms (200 IU)