Overall, those most at risk for a vitamin-D deficiency were older, female, obese, drank milk less than once a week, and spent more than four hours a day watching TV, playing video games, or working on a computer.

CNN: Vitamin D deficiency common in U.S. children

However, a vitamin B-12 deficiency is most often due to a lack of a substance called intrinsic factor.

CNN: Vitamin deficiency anemia

Whether or not Clemens can demonstrate a vitamin B-12 deficiency, he is going to have to contend with questions about why chose injections of a vitamin that is found naturally in meat, fish and dairy products or in commercially-produced and readily-available pill form.

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Vitamin B-12 deficiency can result from a diet lacking in vitamin B-12, which is found mainly in meat, eggs and milk.

CNN: Vitamin deficiency anemia

But the scientific evidence that demonstrates such effects has been shown in individuals who have a vitamin B-12 deficiency.

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Taking too much folic acid - over 1mg a day - can mask signs of vitamin B12 deficiency.

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Sight Savers International offers treatment such as cataract operations, to those whose sight can be saved, and educates healthcare workers about potential conditions which could cause blindness - such as vitamin A deficiency in childhood.

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Some succumbed to beriberi -- caused by a vitamin deficiency and easily treatable.

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Vitamin B-12 deficiency anemia caused by a lack of intrinsic factor is called pernicious anemia.

CNN: Vitamin deficiency anemia

Vitamin B-12 deficiency can also be caused by a tapeworm ingested from contaminated fish, because the tapeworm saps nutrients from your body.

CNN: Vitamin deficiency anemia

Professors Brian Wharton and Ian Booth, from the Institutes of Child Health in London and Birmingham, warned that in people with vitamin B12 deficiency, consumption of folic acid may mask a condition called megaloblastic anaemia - which if not picked up can lead to degeneration of the spinal cord.

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Her exam revealed inordinately high levels of gastrin--an indicator of atrophic gastritis or pernicious anemia, a deficiency of vitamin B12.

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More than five million children in 15 developing countries have received sachets of vitamin and mineral powders that have been approved by UNICEF and the World Health Organization as a cost-effective treatment for iron deficiency.

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