Vitamin D Part 1—Basics 2


by Jack Norris, RD

More Information on Vitamin D

Contents

Healthy Vitamin D Levels

Vitamin D is important for bones because it can increase calcium absorption when the body signals that it needs calcium. Research has shown that in populations whose calcium intakes are similar to omnivores in the United States, vitamin D is more important than calcium for preventing osteoporosis.

In recent years, vitamin D levels have been associated with many other diseases and some researchers have suggested that the recommended vitamin D levels are too low and many laboratories adjusted their recommended levels upward. The Institute of Medicine has reviewed the research and concluded that the recommended levels shouldn’t be adjusted upward. The controversy has resulted in many people thinking they are deficient in vitamin D when they are not.

Make sure that you’re not trying to raise your levels beyond what the Institute of Medicine says is adequate (50 nmol/l or 20 ng/ml) as there’s no sense in worrying if you cannot seem to get your vitamin D levels twice as high as necessary!

Sources of Vitamin D

Most people get a significant amount of their vitamin D from the action of UV rays on their skin. While the body can store vitamin D made in the sunnier months for use during less sunny months, this does not work for everyone. In fact, some people, even those living in sunny climates, develop extremely low levels of vitamin D. This can manifest itself through fatigue and bone pain.

The only significant, natural, dietary sources of vitamin D are fatty fish, eggs (if chickens have been fed vitamin D), and mushrooms (if treated with UV rays). Most Americans get their dietary vitamin D through fortified milk and fortified margarine.

The vegan diet contains little, if any, vitamin D without fortified foods or supplements. On average, vegans’ vitamin D levels are adequate, but somewhat lower than non-vegans.

There are two forms of supplemental vitamin D: ergocalciferol (D2) and cholecalciferol (D3). Vitamin D2 is always vegan, made from exposing fungi to UV rays. Vitamin D3 normally comes from fish oil or sheep’s wool, but there is a vegan version made by Vitashine.

A great deal of research has compared vitamin D2 to D3. Vitamin D2 is effective at increasing bone mineral density (when given to people who are deficient). Vitamin D2 can also increase vitamin D levels temporarily but is not as effective as vitamin D3 at keeping vitamin D levels raised when taken only weekly.

Thus, if you take vitamin D on a daily basis, D2 should be fine, whereas if you’re only going to take it sporadically, without getting sun in the interim, or find that your vitamin D levels will not increase on D2, then you should opt for D3.

Daily Needs

Please see our list of Daily Needs for how to obtain adequate vitamin D.


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  • If you have a question about whether it's okay to cut supplements in half or combine supplements to achieve the dose we recommend, the answer is “Yes.” Be aware that nutrient recommendations are only estimates—it's not necessary to consume the exact amount we recommend every single day.
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2 thoughts on “Vitamin D Part 1—Basics

  • Martin

    I am currently taking a Deva Multivitamin, which has 400 IU Vitamin D2. Your daily needs page recommends 600 IU. Should I take another Vitamin D supplement in addition to this? My last blood test showed low Vitamin D levels (17 ng/mL). I didn’t take any supplements at that time.

    • Reed Mangels

      The Recommended Dietary Allowance (RDA) for people age 9-70 years old is 600 IU/day of vitamin D. Vitamin D is stored by our bodies so you may want to think about how much you should get over a longer time period than a day – a week, say – and how much of the supplement you would need to take to achieve this. 600 IU/day x 7 days/week = 4200 IU/week. Taking 1 tablet 3 days a week and 2 tablets the other 4 days would give you 4400 IU (not exactly 4200 IU but close enough). Also consider if you’re regularly getting other vitamin D sources like plant milks fortified with vitamin D. They often supply 100 IU or more in 8-ounces so could add to the vitamin D from the supplement. Sunlight exposure is also an option but it sounds as if your sun exposure wasn’t adequate to keep your blood vitamin D levels in an acceptable range.