Vitamin D specifically the form D3 is the only vitamin your body makes itself. Its fat-soluble, which means your body stores vitamin D in its adipose tissue in its fat. And, if you want to be specific about things, this vitamin is actually a hormone.
Why we need exposure to the sun daily for vitamin D
Vitamin D helps the body absorb calcium, increase bone density and reduces the risk of soft, weak bones, as well as bone fractures. It also helps with the bodys bone development and muscle function, helps keep the immune system healthy, and helps keep insulin, calcium and phosphorus levels in balance. And emerging research is finding promising associations between our vitamin D consumption and decreased our risk of developing a variety of conditions including autoimmune diseases, cardiovascular disease, chronic inflammation, certain cancers and diabetes.
Sun Exposure &Vitamin D | Skin Care Guide
While vitamin D is all of these things, it might best be known as the sunshine vitamin. How much sunshine your body needs to boost vitamin D levels and how best to get it is up for debate.
Since 2010, the recommended daily allowance (RDA) of vitamin D falls between 600 and 800 International Unit (IU) per day (based on age), but new research suggests adults may actually need at least 2,000 IU of vitamin D every day to maintain a healthy level in the body and reap the most benefits [source: MayoClinic, Holick].
There are two ways we get our D other than exposure to sunlight: Diet and supplements.
In your diet, you can get a natural form of vitamin D3 from foods such as egg yolks (one yolk has 20 IU of vitamin D) and fatty fish (youll get 400 IU of vitamin D from 5 ounces of salmon). Alternatively, look for cereals, juices and other D-fortified foods to supplement your D intake. Milk, for example, is fortified with 100 IU per cup.
Realistically, though, not many of us can count on getting all our vitamin D needs from diet alone. Enter supplements. But the most efficient way to ensure your body gets the right amount? Let it make the D itself.
How Your Body Converts Sunlight Into Vitamin D
Your body is able to produce its own vitamin D3 whenyour skin is exposed to the suns ultraviolet rays, specifically ultraviolet (UVB) radiation. When UVB rays hit your skin, a chemical reaction happens: Your body begins the process of converting a prohormonein the skin into vitamin D. In this process, a form of cholesterol called 7-dehydrocholesterol (7-DHC), naturally found in your skin, absorbs the UVB radiation and gets converted into cholecalciferol. Cholecalciferol is the previtamin form of D3. Next, the previtamin travels through your bloodstream to your liver, where the body begins to metabolize it, turning it into hydroxyvitamin D, which is also known as 25-hydroxyvitamin D or 25(OH)D. The kidneys then convert the 25(OH)D into dihydroxyvitamin D, also called 1,25-dihydroxyvitamin D or 25(OH)2D this is the hormone form of vitamin D your body can use [sources: The George Mateljan Foundation, Holick].
Its estimated that we get or should get more than 90 percent of our vitamin D from casual, daily sun exposure [source: Holick]. Lets figure out what casual, daily sun exposure means. There are variables, which well talk about, but some studies have found that between five and 30 minutes of sun exposure to your unprotected face, arms, legs or back between the hours of 10 a.m. and 3 p.m. two to three times every week is enough for your body to produce all the D3 it needs [source: National Institutes of Health - Office of Dietary Supplements].
Under picture-perfect conditions, the human body is able to produce as much as 10,000 IU to 20,000 IU of vitamin D3 in just 30 minutes [source: The George Mateljan Foundation]. Yet vitamin D deficiencies are rising among all age groups in the U.S. Its estimated as many as half of all children, teens and young adults are vitamin D deficient, as are as many as 25 to 57 percent of American adults [source: Lee]. We dont often encounter those perfect conditions for vitamin D production, so lets look at some of the reasons we might not be making enough D3.