Your skin synthesizes the sunlight's ultraviolet-B radiation into the fat-soluble vitamin D3, or cholecalciferol, essential for metabolic function of calcium in the liver, kidneys and bones, as well as nervous and immune system maintenance. Half of the world's population does not receive enough D3 from sunlight, and must supplement their recommended daily requirement through diet or supplements.
How Vitamin D3 Works
Two forms of vitamin D exist in nature. Cholecalciferol is processed by humans, while ergosterol, or D2, is made by plants. Vitamin D3 is inactive on its own and must be metabolized, sent through the bloodstream and processed in the liver, where the molecule hydroxyl attaches itself to D3 to form calcidiol. According to the Linus Pauling Institute, calcidiol circulates through your bloodstream, activating more than 50 genetic molecular interactions vital to human life, including serum calcium. This is why you need D3 in your body, as a catalyst to keep calcium in check and the body functioning at healthy levels.
Calcium and D3
If serum calcium levels drop too low, your parathyroid glands, located in your neck behind your thyroid, will secrete parathormone, or PTH. The rise in PTH increases the D3 enzyme in your kidneys, which in turn increases metabolized D3 production, normalizing serum calcium. Your intestines begin to better absorb calcium while your kidneys filter calcium more efficiently. If you still need a boost in serum calcium levels, your bones provide it.
D3 Insufficiency
Your physician might prescribe a D3 supplement if lab tests detect an insufficient level of vitamin D in your bloodstream. Vitamin D insufficiency, or levels that fall between 30 and 50 nmol/L that is not corrected, can lead to D3 deficiency and diseases such as osteoporosis in adults and rickets in children. The National Institutes of Health's Office of Dietary Supplements recommends vitamin D levels equal or greater than 50 nmol/L, an amount that would be adequate for people in good health. Nearly 98 percent of the world's population needs that amount to be D3-sufficient.
D3 Deficiency
Vitamin D levels less than 30 nmol/L are considered D3 deficient. At this point, you might benefit from supplementation with prescription or over-the-counter D3 formulations. Side effects might include feeling tired or thirsty, with diarrhea or constipation and a poor appetite leading to weight loss. If you take cardiac medicine, have kidney or heart disease, high blood calcium or phosphorus, consult your doctor before adding a D3 supplement to your diet. Salmon, mackerel, cod liver oil and eggs are nature's best sources of vitamin D.
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