Sometimes called the "sunshine vitamin," many people think of vitamin D as the nutrient they absorb from the sun. The sun rays themselves don’t actually contain any vitamin D; instead, skin that is penetrated by specific ultraviolet rays works to synthesize this energy into vitamin D, starting a process involving the liver and kidneys to create the essential hormone calcitriol.
Vitamin D functions as a precursor to the hormone calcitriol, which current research finds plays a major role in how cells are developed and maintained. This makes vitamin D different from other vitamins that fuel bodily processes rather than direct them. As a fat-soluble vitamin, excess vitamin D is stored in the body’s fatty tissues rather than being excreted through the kidneys like water-soluble vitamins, such as vitamin C and the various B vitamins.
The Effects of Sunlight & Fresh Air on the Body
Vitamin D plays many roles in the body, primarily promoting the uptake of calcium in the small intestine during the digestive process. Without vitamin D, proper mineralization of the bones cannot occur, including the building and remodeling of bones 1. Deficiencies can lead to rickets in children and osteomalacia and osteoporosis in adults. Vitamin D helps regulate the amount of calcium and phosphorus in the blood, reduce inflammation, support immune function and modulate the development of proteins involved with gene encoding.
- Vitamin D plays many roles in the body, primarily promoting the uptake of calcium in the small intestine during the digestive process.
- Vitamin D helps regulate the amount of calcium and phosphorus in the blood, reduce inflammation, support immune function and modulate the development of proteins involved with gene encoding.
Vitamin D Sources
Specific sunlight kicks off the vitamin D synthesis process. According to the National Institutes of Health’s Office of Dietary Supplements, "Ultraviolet (UV) B radiation with a wavelength of 290-315 nanometers penetrates uncovered skin and converts cutaneous 7-dehydrocholesterol to previtamin D3, which in turn becomes vitamin D3." Other non-sun sources include:
- sockeye salmon
- cod liver oil
- fortified dairy
- as well as supplements
- since vitamin D doesn’t naturally occur in significant amounts in other forms
How to Get It
Which Vitamin Do Humans Get From the Sun?
The best way to receive sufficient UVB rays to facilitate vitamin D synthesis requires a balance of enough sun, but not so much as to increase the risk of skin cancer. Just a few minutes of exposure a day provide enough UVB to kick off the vitamin D process. People with darker skin need more time in the sun than those with fair skin, due to their skin’s melanin, which impedes absorption. Researchers suggest spending five to 30 minutes in the sun between the hours of 10 a.m. and 3 p.m. twice a week, to replenish your vitamin D stores. For people at higher risk of skin cancer, or for people with sedentary, indoor lives, supplements work as well.
- The best way to receive sufficient UVB rays to facilitate vitamin D synthesis requires a balance of enough sun, but not so much as to increase the risk of skin cancer.
What Prevents Absorption
Location, season and physical blocks can prevent UVB absorption. Regions north of latitude 40, running horizontally from northern California to New York City do not receive sufficient sun rays from September through May. In addition, anything physically blocking the sun’s rays impedes vitamin D synthesis, such as:
- sunscreen with a sun protection factor higher than 15
- coatings on windows
- clouds in the sky
People with darker skin also require more sunlight, as their higher amount of melanin reduces their UVB exposure.
The Effects of Sunlight & Fresh Air on the Body
Which Vitamin Do Humans Get From the Sun?
The Best Vitamin for Sagging Facial Skin
How to Stop Skin From Getting Darker From the Sun
Natural Remedies for Vitamin D Deficiency
Vitamin D & Excessive Sweating
Cellphones and Hidden Radiation: Is There Evidence of Harm?
How to Protect Skin in the Sun Without Sunscreen
What Vitamins Promote Bone Healing?
Vitamin D and Melanin
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Stephanie Bird started writing and editing for publications in 1998, including the "Chico News & Review" and "Enterprise-Record." Since 1999 she has focused on nutrition and food sensitivities. She currently studies at California State University, Chico, and is a member of the Society for Nutrition Education.