A basic primer on vitamin D
The days are getting longer, the temperature is getting warmer, and the sun is getting stronger. The season of making vitamin D naturally is almost here!
Here’s a basic primer on Vitamin D.
What does it do for your body?
Vitamin D is responsible for bone and muscle health, immunity, calcium and phosphate regulation, cardiovascular health, and cognitive health. It’s a fat-soluble vitamin, meaning it should be consumed with fat to maximize its absorption in the body.
Where can it be found?
Vitamin D is found in a few foods naturally: fatty fish, liver, beef, and fortified foods such as cereals, dairy, and juice (which means the Vitamin D is added, not naturally occurring). Vitamin D is the only vitamin that your body naturally makes.
The body’s main source of vitamin D is made in the skin after outdoor sun exposure. This is a more abundant and usable source than from food.
The conversion of sunlight to vitamin D in the body is complex, but here’s a quick summary:
The sun’s UVB rays, at exactly the right wavelength, touch the skin and convert cholesterol to vitamin D3.
In the liver and kidneys, vitamin D3 is then metabolized into 25-hydroxyvitamin D3 (which is what’s measured when you get a blood test), then 1,25-dihydroxyvitamin D (which is the active form). This form of vitamin D is circulated through the body and is active in many processes.
Why aren’t you able to make vitamin D in your skin in the winter, even if it’s sunny and you’re naked?
The sun doesn’t emit the proper wavelength of UVB (290-315 nm) to activate cholesterol in the skin. This only occurs from about October to April in northern latitudes. Once you get below about Washington, D.C. on the East Coast, you don’t have to worry so much.
So, what should northern dwellers do during these months in order to get vitamin D? First, you want to check if your vitamin D levels are actually low. Studies have shown that supplementation on top of a normal vitamin D level in mostly healthy people doesn’t really do anything at all.
What if you’re low in vitamin D?
If your body is low in vitamin D stores, your choices are foods or a supplement. Relying on food sources alone can make it challenging to get the recommended 600-800 IUs per day of vitamin D. Most supplements are 1,000-4,000 IUs per day, which is recommended since the body is not able to absorb the full amount in the supplement. We think that 4,000 IUs is the upper limit, though one study found that long-term supplementation with mega-doses up to 10,000 IUs was actually harmful for long-term bone health. When buying a supplement look for vitamin D3, which is the most absorbable form in the body.
In the summer months, you can make up to 1,000 IUs of vitamin D in 15 minutes of sunlight, even with sunscreen on! It isn’t necessary to continue vitamin D supplementation in the spring and summer months if you’re getting daily sunshine. If not, it’s recommended to continue seeking out rich food sources or supplementation.
Want to learn more about vitamin D? Check out this Instagram post: You can dance naked on the streets in the winter and not make an ounce of vitamin D.