Everything You Need to Know About Vitamin D

By Katie Trant | Last Updated: August 8, 2016

Everything You Need to Know About Vitamin D

Everything You Need to Know About Vitamin D
The sun is shining these days, but as they say, winter is coming. It’s time to think about vitamin D.

What is Vitamin D?

Here’s a bit of party trivia for you: vitamin D, it turns out, isn’t a vitamin at all – it was misclassified when it was first discovered in the 1920’s, and the name stuck. Vitamin D is, in fact, a pro-hormone: precursors of hormones that amplify the effects of existing hormones.

Almost all cells and tissues in the body are able to convert vitamin D into its active hormone form – there are 2800 known vitamin D binding sites on our DNA!

Why is Vitamin D important?

Vitamin D helps form our bones and teeth, maintains bone health, regulates blood calcium levels, and contributes to our metabolism, nervous system, and immune system function.

We know the most about vitamin D as it relates to bone health, as it helps the body to absorb calcium. A vitamin D deficiency leads to nutritional rickets, a condition that causes deformed and weak bones in infants and children – this is why vitamin D drops are usually recommended from birth. In adults not getting enough Vitamin D can increase the risk of developing osteoporosis.

Aside from bone health, vitamin D has been linked with diabetes, cardiovascular disease, depression, breast, colon, and prostate cancer, autoimmune diseases, influenza, and the common cold.

What’s the deal with D2 vs D3?

In nutrition terms, vitamin D is used to refer to either D2 (ergocalciferol) or D3 (cholecaliferol). D3 is synthesized from cholesterol in our skin when sun exposure is adequate (with enough UVB). D3 can also be found in some foods, such as fatty fish and egg yolks, in fortified foods such as milk and orange juice, and in supplements.

D3 supplements are manufactured through the UV irradiation of a substance derived from sheep’s wool. This means that unless you’re getting your D3 from sun exposure, it isn’t considered vegan.

D2 is the vegan version, made from mushrooms or yeast irradiated under UV light and is used to fortify non-dairy beverages such as soy and almond milk, and is also found in some supplements. It is generally accepted that D2 is less potent than D3.

Can I get adequate vitamin D from sunlight?

This really depends on where you live, and other lifestyle factors. For example, anything that blocks UVB rays will also block vitamin D production by our skin. This includes sunscreen, clothing, complexion, windows, etc.

If you live above 42° North latitude (think Portland, Oregon or just north of Rome, Italy) you could stand outside buck-naked all winter long and never produce enough vitamin D. In these latitudes it’s safe to assume your skin can’t make any vitamin D from about October to April due to lack of UVB. And really, most of us aren’t outside in shorts and a t-shirt until around June. That’s a good chunk of the year we’re not any vitamin D from the sun.

Vitamin D and vegetarians

Some studies have found vegans to have lower vitamin D intakes than lacto-ovo vegetarians or omnivores, yet any person who does not include good sources of vitamin D in their diet or take supplements can be at risk for not getting enough, especially in northern climates where sunlight exposure is limited.

If you’re found to be deficient in vitamin D and choose to take the vegan supplement D2, you may be advised to take a higher dose than if you were to take D3, which is not vegan but is generally believed to be more potent.

How much do I need?

For adults the recommended daily intake of Vitamin D from all sources including sunlight, fortified, foods, and supplementation is 15 micrograms (mcg)/600 international units IU. More recent research on the role of vitamin D suggests that higher intakes may be beneficial, and some experts are recommending 800 IU or more per day for the average adult, with higher intakes recommended to treat deficiency.

If you’re concerned about vitamin D deficiency, speak to your doctor about getting tested.

Can I take too much?

Yes, but it’s pretty unlikely that you will. Vitamin D is one of the fat soluble vitamins (along with vitamins A, E, and K) which means that we store rather than excrete the excess.

Excess vitamin D can cause the body to absorb too much calcium, which in turn can lead to kidney damage. Exactly how much is too much is a matter of debate. Some researchers report using up to 10,000 IU per day without observing problems, however the tolerable upper limit has been set at 4000 IU per day for those over 9 years of age. A conservative recommendation is to stay below 2000 IU per day.

Despite the all of these claims regarding the benefits of vitamin D there is still a lot of disagreement amongst the scientific community regarding it’s efficacy as a supplement. The only proven benefit is in helping calcium to build strong bones, but we do know that vitamin D helps regulate the immune system and neuromuscular system. Exactly how this happens is not yet well understood.

The Bottom Line

The vast majority of research continues to show that vitamin D does reduce the risk of many chronic diseases. More research is needed, but future research will likely shed light on the exactly how and why vitamin D is beneficial.

Vitamin D image via Shutterstock

About Katie Trant

Katie is a university-trained nutritionist and professional writer based in Stockholm, Sweden. She is a vegetarian of more than two decades, and is passionate about real food. Her blog The Muffin Myth is all about approachable nutrition.

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