Everything you need to know about vitamin D

vitamin-dVitamin D is commonly remembered as the vitamin we get from sun exposure.

After decades of research, scientists are still unable to pin down the true nature of this vitamin and what it can do for health, although we know Vitamin D helps the body absorb calcium.

On the one hand, vitamin D has gained a reputation in just the last few years as a “wonder” vitamin with powers over cancer, heart attack, Alzheimer’s disease, and other serious conditions.

On the other hand, numerous reports suggest the fallacy of these vitamin D health claims.

Meanwhile, some doctors argue the population is severely deficient in this important vitamin, while others warn we’re dangerously over-supplementing ourselves (1).

What’s the real story about vitamin D?

You’ll also get answers to questions like these:

  • Are we getting enough or too much vitamin D?
  • What can it really do for our health?
  • Are there side effects if you take too much?
  • What’s considered too much?

Here’s what we know for sure about vitamin D

What we do know for sure is that vitamin D helps the body absorb calcium.  For that reason alone, it’s crucial that we get enough of this important vitamin in our diets.  After all, calcium (along with phosphate) is the essential building block of bones.  If you don’t get enough calcium in your diet, or if you aren’t absorbing the calcium you do consume, bone production and bone tissue are severely impacted.

Beyond that, the role of vitamin D and its effect on health is highly debated.  That doesn’t mean there aren’t additional benefits to supplementation, however.  There simply needs to be more data (more on these possible benefits in just a bit).

Why vitamin D supplements are necessary

It’s estimated that worldwide, around a billion people don’t get enough vitamin D (2).

There are very few food sources of vitamin D, but beef liver, cheese, mushrooms, and egg yolks provide tiny amounts.

Fatty fish provide even more, but the best way to get your vitamin D is to drink fortified milk, get 15 minutes of sunshine every day, or take supplements.

In fact, it’s very difficult to get all the vitamin D from food sources.

Likewise, if you live in a northern part of the world it can be hard to get your vitamin D from sunshine, too. Not only that, but certain segments of the population have trouble getting enough of the vitamin from the sun, too: people with dark skin.

Finally, the elderly need more vitamin D than the rest of us.

For all these reasons, vitamin D supplements are among the most widely necessary supplements on the planet.

Vitamin D toxicity

Did you know there’s something called vitamin D toxicity?  Vitamin D supplementation may be necessary for much of the population, but more doesn’t always equal better.  Vitamin D toxicity almost always comes from supplements.

It’s easier to get too much vitamin D than other vitamins.  Like vitamins A, E and K,  is a fat-soluble vitamin which are easy to overdose.

Therefore, it’s important to recognize what’s officially known as the “Safe Upper Limits” for daily vitamin D intake. These are the MAXIMUM levels considered safe (400 IU is equal to 10 mcg.)

The U.S. National Library of Medicine (3) gives the following Safe Upper Limits for vitamin D:

  • Infants: 1,000 to 1,500 IU/day
  • Children 1-8 years: 2,00 to 3,000 IU/day
  • Everyone else: 4,000 IU/day

Keeping within those Safe Upper Limits, dosages of vitamin D are believed to have a wide range of health benefits.  Here’s where things get a little confusing.

Confusion over causation vs. correlation causes confusion over the benefits of vitamin D

Extra vitamin D has been attributed to a whole series of wonderful benefits, not the least of which is preventing fractures in the elderly.  While that seems to be pretty well grounded in scientific data, other health claims are a little less clear.

Ongoing research reveals many possible applications of vitamin D supplements, but this is where the confusion begins.

Every time there’s a new study, the media takes that news and runs with it.  For example, even a very a weak data link between vitamin D and lower incidences of cancer produces a flurry of reports that vitamin D is the new cancer-preventing drug.  A mere suggestion that people who live longer tend to have optimal levels of vitamin D leads to reports that D supplements will make us live longer…even though there’s no clear indication whether it’s causation or correlation between longevity and vitamin D.

What can vitamin D supplements really do for you?  

But there is actually some promising research suggesting vitamin D can help in many areas of health.  Here are the areas which show more than just a faint possibility of good things happening from taking vitamin D supplements:

  • Cancer.  30 years ago, it was discovered that people living in northern areas had higher rates of colon cancer (4).  That led to the theory that lower vitamin D levels might increase colon cancer risk.  Dozens of studies have been performed since then that strongly support the theory, but that doesn’t necessarily mean vitamin D supplements will lower the risk.
  • Heart Disease.  A 20 year study (5) found that men with vitamin D deficiencies had double the risk of having a heart attack.  There’s a strong link between D and heart health, but more research is needed.
  • Multiple Sclerosis.  MS rates are higher in the north and one study (6) showed that white people with higher vitamin D levels had a 62% lower risk of contracting MS.  That study did not find this to be the case with black people, so the link between D and MS is weak.  Nevertheless, there is hope.
  • The Common Cold. A study performed in 2012 indicates that when kids take vitamin D, their chance of getting a cold decreases by 50% (7).
  • Type 1 Diabetes.  A child in Finland is around 400 times more likely to develop Type 1 Diabetes than a child living in Venezuela (8).  Since there is less sun in Finland (therefore lower vitamin D levels), this suggests a link between vitamin D and the disease.

The bottom line

There is danger in taking too much, and beyond bone health, the disease-fighting properties are not yet confirmed by science.


  1. Wasson, Nick.  Vitamin D Supplement Dosage Warning.  Retrieved 9/1/2015 from http://abcnews.go.com/blogs/health/2013/02/11/vitamin-d-supplement-dosage-warning/
  2. Vitamin D and Health.  Harvard School of Public Health.  Retrieved 9/13/2015 from http://www.hsph.harvard.edu/nutritionsource/vitamin-d/
  3. Vitamin D.  Medline Plus.  U. S. National Library of Medicine.  Retrieved 9/13/2015 from https://www.nlm.nih.gov/medlineplus/ency/article/002405.htm
  4. Garland CF, Garland FC. Do sunlight and vitamin D reduce the likelihood of colon cancer? Int J Epidemiol. 1980; 9:227-31.  Retrieved 9/13/2015 from http://ije.oxfordjournals.org/content/9/3/227.short
  5. Giovannucci E, Liu Y, Hollis BW, Rimm EB. 25-hydroxyvitamin D and risk of myocardial infarction in men: a prospective study. Arch Intern Med. 2008; 168:1174-80. Retrieved 9/13/2015
  6. Munger KL, Levin LI, Hollis BW, Howard NS, Ascherio A. Serum 25-hydroxyvitamin D levels and risk of multiple sclerosis. JAMA. 2006; 296:2832-8.  Retrieved 9/13/2015 from http://jama.jamanetwork.com/article.aspx?articleid=204651
  7. Abrams, Kindsay.  Study: Vitamin D Supplements May Protect From Colds.  The Atlantic Monthly.  Retrieved 9/13/2015 from http://www.theatlantic.com/health/archive/2012/08/study-vitamin-d-supplements-may-protect-from-colds/261347/
  8. Gillespie KM. Type 1 diabetes: pathogenesis and prevention. CMAJ.2006; 175:165-70.  Retrieved 9/13/2015 from http://www.cmaj.ca/content/175/2/165.full
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