When some of our family moved to the Pacific Northwest, they were advised to start taking large dosages of Vitamin D.  Not only did the lack of sunshine curtail the necessary sun exposure so that the skin cells were able to make its own, the American Academy of Pediatrics (AAP) doubled its Vitamin D recommendations to 400 IUs per day back in 2008.

Vitamin D deficiency was first linked to rickets - a childhood malady where bones form improperly, typically causing bone weakness and breakage - back in the early 1900s.  Some blame the increase in rickets on the amount of smoke pouring from factories (thus obscuring the sun's rays).  Whatever the reason, scientist realized Vitamin D, which is also called calciferol, was necessary for skeletal health.  More recent studies have shown that low levels of Vitamin D may exacerbate depression and seasonal affective disorder (SAD), cystic fibrosis, diabetes and some forms of cancer.

The risks associated with low levels of Vitamin D are still being explored, but it's already clear that getting a minimum amount is important for one's health.  A word of warning about Vitamin D: as with all fat-soluble vitamins, it is important not to get too much because of the problems associated with toxicity (symptoms include nausea, vomiting, poor appetite, constipation, weakness, and weight loss as well as excessive blood levels of calcium, which can cause confusion and heart rhythm abnormalities). 

So how do you get enough?  In the late 1800s, German scientists promoted a tablespoon of codfish liver oil every day.  It's still one of the best sources of Vitamin D.  But here's the kicker: those German scientists were also promoting (albeit unknowingly) increased amounts of Omega-3 fatty acids that help with brain development and eye function.  Lesson from this: take your codfish liver oil supplement!

Here's a table from National Institute of Health's Office of Dietary Supplements:

Table 3: Selected Food Sources of Vitamin D [30]

Food	IUs per serving*	Percent DV**
Cod liver oil, 1 tablespoon	1,360	340
Salmon (sockeye), cooked, 3 ounces	794	199
Mushrooms that have been exposed to ultraviolet light to increase vitamin D, 3 ounces (not yet commonly available)	400	100
Mackerel, cooked, 3 ounces	388	97
Tuna fish, canned in water, drained, 3 ounces	154	39
Milk, nonfat, reduced fat, and whole, vitamin D-fortified, 1 cup	115-124	29-31
Orange juice fortified with vitamin D, 1 cup (check product labels, as amount of added vitamin D varies)	100	25
Yogurt, fortified with 20% of the DV for vitamin D, 6 ounces (more heavily fortified yogurts provide more of the DV)	80	20
Margarine, fortified, 1 tablespoon	60	15
Sardines, canned in oil, drained, 2 sardines	46	12
Liver, beef, cooked, 3.5 ounces	46	12
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)	40	10
Egg, 1 whole (vitamin D is found in yolk)	25	6
Cheese, Swiss, 1 ounce	6	2
*IUs = International Units. **DV = Daily Value. DVs were developed by the U.S. Food and Drug Administration to help consumers compare the nutrient contents of products within the context of a total diet. The DV for vitamin D is 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. The U.S. Department of Agriculture's Nutrient Database Web site, http://www.nal.usda.gov/fnic/foodcomp/search, lists the nutrient content of many foods and provides a list of foods containing vitamin D: http://www.ars.usda.gov/SP2UserFiles/Place/12354500/Data/SR22/nutrlist/sr22a324.pdf. A growing number of foods are being analyzed for vitamin D content. Simpler and faster methods to measure vitamin D in foods are needed, as are food standard reference materials with certified values for vitamin D to ensure accurate measurements [31].