Tuesday, May 22, 2012

The "SUNSHINE" Vitamin - Vitamin D

There has been a lot of news over the last year or two about the benefits of Vitamin D. A lot of this is potentially exciting, but medical bodies have been at odds over how MUCH exactly to recommend. A lot of the benefits are NOT YET 100% factual, but derived from observational trends.  This is potentially promising and exciting, but we physicians tend to err on the side of caution, rather than go overboard too early. (That can get embarrassing, if the evidence shows us to be wrong down the road. . .)

Let's try and sort out what's worth doing. . .

What does Vitamin D do?
Vitamin D, like all vitamins, is a nutrient that our body can NOT produce on its own, so we need to get it from outside sources.  It has a number of functions in our body:

  • Helps the gut to absorb Calcium
  • Plays a definite role in Bone strength and structure
  • May be cardioprotective. (Low levels increase risk of heart attack and stroke)
  • May DECREASE the risk of Colon Cancer
  • May Prevent Multiple Sclerosis
  • May Prevent Viral Infections like the Flu
  • May Decrease the risk of Diabetes.


Uncovered skin to sun allows UVB rays to convert Previtamin D to Active Vitamin D3. There are a lot of factors that affect the amount of conversion including the time of year, time of day, skin tone, geographic location, pollution, sunscreen etc., but scientists estimate that anywhere from 5-30 minutes of sun exposure to face, arms and legs twice a week would be more than enough to maintain adequate active Vitamin D stores. The downside is, obviously, that too much sun exposure is a significant risk factor for skin cancer!

I should make special note that in Northern Climates, (including northern U.S. States, and Canada), during winter, an adequate supply from sun is NOT available, and supplements should be considered, especially for infants and young children.

(Yes, that is Canadian Milk in a Bag on the right!)


Other than some fatty fish, very few foods contain any significant levels of Vitamin D. Given this, some foods are fortified with Vitamin D, the most important being MILK. Some juices, yogurt, cereals etc are also fortified, but you need to look carefully to ensure this.

ALL infant formulas in the US and Canada are fortified by law. (Please note, although I strongly encourage breast feeding, the amount of Vitamin D in breast milk is NOT adequate on its own).

(chart from NIH, Office of Dietary Supplements)  - NIH
Table 3: Selected Food Sources of Vitamin D [11]
FoodIUs per serving*Percent DV**
Cod liver oil, 1 tablespoon1,360340
Swordfish, cooked, 3 ounces566142
Salmon (sockeye), cooked, 3 ounces447112
Tuna fish, canned in water, drained, 3 ounces15439
Orange juice fortified with vitamin D, 1 cup (check product labels, as amount of added vitamin D varies)13734
Milk, nonfat, reduced fat, and whole, vitamin D-fortified, 1 cup115-12429-31
Yogurt, fortified with 20% of the DV for vitamin D, 6 ounces (more heavily fortified yogurts provide more of the DV)8020
Margarine, fortified, 1 tablespoon6015
Sardines, canned in oil, drained, 2 sardines4612
Liver, beef, cooked, 3 ounces4211
Egg, 1 large (vitamin D is found in yolk)4110
Ready-to-eat cereal, fortified with 10% of the DV for vitamin D, 0.75-1 cup (more heavily fortified cereals might provide more of the DV)4010
Cheese, Swiss, 1 ounce62

* IUs = International Units.
** DV = Daily Value. DVs were developed by the U.S. Food and Drug Administration to help consumers compare the nutrient contents among products within the context of a total daily diet. The DV for vitamin D is currently set at 400 IU for adults and children age 4 and older. Food labels, however, are not required to list vitamin D content unless a food has been fortified with this nutrient. Foods providing 20% or more of the DV are considered to be high sources of a nutrient, but foods providing lower percentages of the DV also contribute to a healthful diet.

How Much Should I Take?

Various Governing Medical Bodies have come out with recommendations based on the available incomplete evidence and studies. Many studies are currently underway trying to come out with an appropriate safe number while maximizing benefit. Given that toxicity is unlikely to occur below an intake of 10,000 IU Vitamin D a day, I believe the Canadian Guidelines (CMAJ, Sept 7, 2010) of 1000 IU of Vitamin D/ day is an appropriate place to start. Here is the equivalent link for the U.S. (US Preventive Task Force, Dec 2011)

Bottom Line: Get a little bit of sun, drink your milk, and in the wintertime take 1000 IU Vitamin D supplement.

Please let me know what you think of the blog so far. Loving the comments and suggestions!

(Special Thanks to the SE Water Cooler)

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