When Vitamin D Supplements May Be Necessary

I recently attended the first-ever International Sports and Exercise Nutrition Conference in Newcastle England, and I’m nearly bursting at the seams with new information to share! One of the most interesting presentations was on vitamin D, a current “hot” topic in nutrition. Dr. Enette Larson-Meyer, a renowned dietitian and researcher at the University of Wyoming, shed light on the issue in her presentation.

There is a lot of buzz about this nutrient right now because research has linked it to many aspects of health (see below). Though the research isn’t 100% conclusive (is it ever?), there are many dietitians and other health care professionals who now recommend vitamin D supplements for many of their patients. Let’s talk about the reason behind these recommendations.

Why do we need vitamin D? It helps maintain immune function and prevent against illness, which is especially important during the winter cold and flu season. It is also crucial for muscle function and helps maintain bone strength by increasing the absorption of calcium from our diets.


Photo: Flickr via Guillaume Cattiaux


What are the sources? Our bodies can make vitamin D by absorbing it through sunlight (specifically UVB rays), but this is not possible during the winter months in locations greater than 35 degrees latitude North or South. In addition, covering the skin with clothing or sun screen blocks absorption, so it’s often difficult for people to get enough vitamin D just from the sun. The other source of vitamin D is food, but the options are rather limited (especially for those who don’t like fish)! Here is a list of the best sources, according to the NIH’s Office of Dietary Supplements:


IUs per serving

Cod liver oil, 1 tablespoon


Swordfish, cooked, 3 ounces


Salmon (sockeye), cooked, 3 ounces


Tuna fish, canned in water, drained, 3 ounces


Orange juice fortified with vit D, 1 cup (check product labels, as amount of added vit D varies)


Milk, nonfat, reduced fat, and whole, vitamin D-fortified, 1 cup


Yogurt, fortified with 20% of the DV for vitamin D, 6 ounces (more heavily fortified   yogurts provide more of the DV)


Margarine, fortified, 1 tablespoon


Sardines, canned in oil, drained, 2 sardines


Liver, beef, cooked, 3 ounces


Egg, 1 large (vitamin D is found in yolk)


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)


Cheese, Swiss, 1 ounce



Who needs a supplement? Well, take a look at the list above— if you don’t eat the foods listed very often, and you don’t get out in the sunshine much, then you may need to consider a supplement. Even many athletes, who generally spend significant amounts of time outdoors and eat more food than their non-athletic counterparts, may still be at risk. Older adults, breastfed infants, and those with dark skin are also higher-risk groups.

Taking a vitamin D supplement can be an effective way to manage a lack of dietary or solar vitamin D intake. However, you should always talk to your health care providers before starting a new supplement!

How much should I take? In the USA, the recommended dietary allowance for adults is 600IU (international units), or 15mcg, per day. A dose of 50-100% the daily recommended intake (which would be 300-600 IU’s or 7-15mcg) is probably enough for most people. But the mantra of “more is better” doesn’t apply here! Taking too much vitamin D can be harmful. Check the label of any product to make sure that it doesn’t exceed 4000 IU (100mcg), which is the upper limit for safe intake of vitamin D. And again, ask a professional before you start any supplements!

UPDATE: Winter making you sleepy?  It might not just be the short days and cold.  It could be your vitamin D status.  A recent study found that people with low vitamin D levels were more likely to experience significant daytime sleepiness compared to people with sufficient levels.  While the study didn’t investigate whether improving vitamin D deficiency fixed sleepiness, it does hint at a connection.  In winter, with much less sunlight, vitamin D production in skin is severely impaired.  If you feel like you need a long nap every day, have your vitamin D checked.


NIH’s Office of Dietary Supplements

Larson-Meyer, E. (Dec 14, 2012). Vitamin D: is there really a deficiency epidemic? At the International Sports and Exercise Nutrition Conference; Newcastle, England.

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