Vitamin D is created by your body when your skin is exposed to ultraviolet light. In areas north of the 45th parallel, the climate is cooler, days are shorter and winters are longer -- all factors leading to a decreased exposure to sunlight. (In North America, this is all of Canada and the northern-most areas of the United States: Washington, Idaho, Montana, North Dakota, much of Minnesota, northern Michigan, northern New England and Alaska.) Several studies have shown that some people living north of the 45th parallel have low serum levels of vitamin D. Another study suggested that even a multiple vitamin with 400 units of vitamin D may not be sufficient to overcome this deficiency; 800 units may be more appropriate if you live this far north. A vitamin D deficiency develops over the long term; the effects are not immediate.

Rickets is seen more frequently in African American infants who have been breast-fed but have not received vitamin D supplements. Increased skin pigmentation blocks ultraviolet (UV) light from producing vitamin D, making darker skinned infants more susceptible to rickets. All breast-fed infants should be given a vitamin supplement containing vitamin D until they are weaned and put on vitamin-D-supplemented milk.

Although polar bear might not be on your menu, it is an important source of protein among the Inuit of Canada and Alaska. Polar bear liver, however, contains high concentrations of vitamin A, sufficient to cause poisoning or even death if ingested in large quantities. Other animals with potentially toxic concentrations of vitamin A in the liver include seal, whale and grouper fish.

In high concentrations, vitamin A is considered a teratogen, meaning it causes birth defects. Vitamin A, however, is essential for the early development of the fetus, so too little vitamin A also can lead to birth defects. Although a folic acid deficiency can lead to birth defects, an excess of folic acid will not cause birth defects.

Deficiency of vitamin A results in a condition called xerophthalmia, which, if not corrected, can lead to permanent blindness. Early deficiency of the vitamin results in xerosis, a condition characterized by dryness of the membranes that cover the cornea and other parts of the eye. If the vitamin A deficiency is not corrected, keratomalacia occurs. This is a softening and ulceration of the cornea that leads to permanent blindness. Programs to provide vitamin A supplements to children in South America and Africa are now in place.

Although a lack of vitamin C had not yet been identified as the cause of scurvy, doctors noticed that supplementing sailors' diets with citrus fruits and fresh vegetables prevented scurvy from developing. Because the sailors had no way of keeping fresh fruits and vegetables during long periods at sea, the British Royal Navy provided lemon and lime juice for them to drink. Vitamin C was not identified until around 1930.

Black currants contain four times the vitamin C of citrus fruits: one cup contains 200 mg -- versus about 120 mg for a cup of orange juice. But black currants aren't widely cultivated in the United States because they are considered too tart to eat fresh. They are more popular in Europe, where they are used to make juice, jams and jellies. Unfortunately, cooking them to make jams and jellies destroys most of the vitamin C. Black currants are not the same as dried currants, which are similar to raisins in texture and nutrition.

Alcoholics may be deficient in many nutritional areas, including a severe thiamin deficiency, vitamin C deficiency, inadequate protein intake and insufficient calories. Other risk factors for scurvy are mental disorders, social isolation among the elderly and eating disorders. Because of food is abundant in the United States and much of it is "fortified" with vitamin C, even otherwise malnourished children are not likely to develop scurvy.