Hi friends! Today we are chatting about Vitamin D, another common nutrient of concern for people on plant-based diets. Heck, this is a nutrient lots of people are concerned about, and the vitamin often comes up in the popular media. So what is Vitamin D? What is the “vitamin D controversy?” How do you know if you are vitamin D deficient? Read on for more vitamin D information!
Disclaimer: As always, this is general information intended for healthy adults. Your needs may vary based on medical status, lifestyle, or life-stage. Please never replace generalized health information you’ve read online with individualized clinical care.
What is vitamin D?
Vitamin D is a fat-soluble vitamin that is found naturally in a very small number of foods. Most people get their vitamin D from fortified foods, and/or the sun.
There are two main dietary forms of vitamin D: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol), which differ in their side-chain structure.
Vitamin D2 is manufactured by UV radiation of ergosterol in yeast, and D3 is manufactured via irradiation of 7-dehydrocholesterol from lanolin. Lanolin is a sheep product, and thus, some do not consider this form of vitamin D purely vegan*.
Both D2 and D3 are well-absorbed. It seems many believe that D3 is somehow superior; in reality, both are considered to be well-absorbed and effective at raising serum levels of vitamin D, with the only major difference being that at very high doses, D2 may be less potent than D3.
*This is why some people do not consider fortified cereals like Cheerios to be 100% vegan; If you are vegan and confused on what to think on the topic, as I am no moral authority on the topic, I encourage you to make the judgement that feels right to you.
What does vitamin D do?
Vitamin D has many functions in the body. It helps promote calcium absorption in the gut by up-regulating a transcription factor that leads to more calcium receptors to rise to the surface of the intestinal tract, and take in calcium. This helps the body maintain adequate blood levels of calcium and phosphate, which support normal mineralization of bones.
Vitamin D is also important for bone growth and remodeling, as well as cellular growth, immune and neuromuscular function. It can also help play a role in reducing inflammation, and many genes that encode proteins that regulate cell proliferation, differentiation and apoptosis are modulated in some capacity by vitamin D.
How much vitamin D do you need?
The RDA for vitamin D is listed in IU and mcg below. For reference, 40IU is equivalent to 1mcg.
- 0-12 months: 400IU (10mcg)
- 1-13 years: 600IU (15mcg)
- 14-70 years: 600IU (15mcg)
- >70 years: 800IU (20mcg)
- Pregnant/breastfeeding: 600IU(15mcg)
What foods contain vitamin D?
As mentioned above, very few foods naturally contain vitamin D. Some fatty fish (like tuna, salmon, and mackerel) contain good sources of vitamin D, and small amounts can be found in egg yolks and beef liver.
Some mushrooms contain vitamin D2, although the amounts they contain varies. Treating mushrooms with UV radiation has been shown to increase their vitamin D2 content.
Most Americans get the vitamin D in their diet from fortified foods. Milk, for example, is voluntarily fortified in the United States, and contains about 100IU/cup. Plant-milks are also often fortified with vitamin D; the exact amount varies brand to brand, so be sure to check labels.
Cereal is also often fortified with vitamin D, although organic and natural brands are typically not fortified. Again, read labels to check how much your favorite products have!
Here are some food sources of vitamin D:
- Salmon (3 ounces): [447IU/112% DV]
- Fortified orange juice (1 cup, check labels as fortification values vary): [137 IU/34% DV]
- Fortified milk (1 cup): [115-124IU/29-31%]
- Mushrooms (1 cup): [~2-17IU, depending on variety, 0.3-3%]
- Swiss cheese (1 ounce): [6IU/2%]
- Fortified cereal: Example – Cheerios (1 cup): [3.4ug/10%]
Vitamin D from Sun Exposure
That’s right, vitamin D, the “sunshine vitamin,” can absolutely be obtained from the sun. In fact, a lot of people meet at least some of their vitamin D needs via sun exposure.
Vitamin D is the only vitamin you can make endogenously (meaning on your own) in your skin, which makes it a pretty neat vitamin!
How? UVB radiation with a wavelength of 290-320 nanometers can penetrate uncovered skin and covert a compound known as 7-dehydrocholesterol to previtamin D3, which then becomes vitamin D3.
Cloud cover, the season, time of day, smog, sunscreen, and melanin content of the skin can all impact the amount of vitamin D synthesized in the skin. Complete cloud cover reduces your ability to make vitamin D from sunlight by 50%, and severe pollution can reduce this ability by up to 60%. Sunscreen with SPF of greater than 8 blocks vitamin D-producing UV rays.…