Most of the vitamin D in your body is created by exposure to sunlight.
"During exposure to sunlight, the high-energy UV photons (290-315 nm) penetrate the epidermis and photolyze 7-dehydrocholesterol (provitamin D3) to previtamin D3. Once formed, previtamin D3 undergoes a thermally induced isomerization to vitamin D3 that takes 2-3 days to reach completion." (Photosynthesis of vitamin D in the skin: effect of environmental and life-style variables )
That is to say, the sunlight hits your skin and you photolyze vitamin D3. Actually, it is previtamin D3. This is the important part as to why you can not obtain the same benefits by taking a vitamin D supplement. Previtamin D is not the only part of the chemical equation you produce while photosynthesizing. There are photo proteins, melatonin, other hormones, and important ingredients your body needs to maintain a healthy immune system (among other things.) Some of these ingredients have unique biologic properties. Unique means you can not obtain them any other way than through sunlight.
"Sunshine may play a role in regulating hormones and sleep patterns by affecting the melatonin circadian rhythm. Melatonin is a hormone produced in the pineal gland, from the chemical melanin. Melanin is produced in the skin through sun exposure. Melatonin helps with inducing sleep." (Sleep, sunshine & vitamin D)
The complex process of photosynthesis and metabolism starts in your skin. Most of the immune system benefits happen from the start of the process (skin) and continue for 2 to 3 days on the way to the blood stream. After a couple days, a small piece of the process makes it into your blood as Vitamin D3. When you take Vitamin D3 supplements, you miss all the benefits of the photosynthesis process, as well as, the "good gut bacteria" process.
IMPORTANT NOTE: There are great risks to exposing your skin to sunlight. Exposure to Ultraviolet (UV) Radiation can cause premature aging of the skin and signs of sun damage such as wrinkles, leathery skin, liver spots, actinic keratosis, and solar elastosis. UV rays can also cause eye problems. Most skin cancers are a result of exposure to the UV rays in sunlight. There are also many people that need to take vitamin D supplements for other reasons. You should talk to your doctor. "Vitamin D supplements have potential harms, such as a risk of hypercalcemia and kidney stones, when given at high doses." (Vitamin, Mineral, and Multivitamin Supplementation to Prevent Cardiovascular Disease and Cancer)
In some cases, vitamin D supplements may be advised by your doctor. Listen to your doctor. For people that can not obtain their Vitamin D from sunlight, you can mimic the Inuit. The Inuit are dark skinned people living out of direct sunlight most of the year. Their bodies have adapted to eating fatty fish to supplement their sun exposure -- Fatty fish and Seafood / Trout 645iu per serving.
For most people, sunlight is the best thing to do. It only takes 30 seconds to a minute-and-a-half of sunlight per day for your body to make enough Vitamin D. The crucial elements of the equation are: how direct the sunlight and how dark the skin. (e.g. If you have dark skin and live in Canada during the winter, you will need a lot more sunlight.) Some studies suggest that once skin is exposed to the sun it becomes increasing less effective at producing D. I try to remember to expose my wrists from time-to-time. The more virgin to sunlight the skin, the better the skin is at creating vitamin D through photosynthesis. It also reduces the amount of time needed exposing the skin to dangerous radiation.
Learn More About Vitamin D and Sunlight
Vitamin D, Health, and Wellness
Good Gut Bacteria (Gut Microbiome)
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