B₁₂/Folate Problem set

Function

Vitamin B₁₂ and folate are distinct nutrients that differ in their synthesis and uptake from the diet. However, they have roles in the body that overlap in one crucial respect- both are cofactors of the enzyme methionine synthase, a key enzyme in the synthesis of the amino acid methionine and the multifunctional cofactor S-adenosyl methionine (SAM). As a result, a deficiency in one of these nutrients can mimic a deficiency in the other. These two "vitamins" are therefore often considered together.

Sources

Humans obtain both vitamin B₁₂ and folate from their diets, and thus the USDA has set minimum daily requirements for each of these essential nutrients. Sources of these vital nutrients are summarized in the table below.

Nutrient	Sources
Vitamin B12	Meat, fish, poultry, fortified cereals
Folate	Leafy green vegetables, whole-grain breads, enriched breads and cereals
Source: USDA Food and Nutrition Information Center (url: http://www.nal.usda.gov/fnic/index.html), viewed June 27, 2006.

Biosynthesis will not be considered in detail for either nutrient. However, it should be noted that biosynthesis of folate in bacteria is a target for antibiotic action.

Effects of Vitamin Deficiencies

In all people, vitamin B₁₂ deficiency leads to impaired red blood cell production and a condition called megoblastic anemia. In addition, approximately 30% of patients with vitamin B₁₂ deficiency have neurological disorders. In infants and small children, vitamin B₁₂ deficiency can also cause developmental defects. There are no natural plant sources of vitamin B₁₂, therefore a strict vegetarian diet, devoid of vitamin-fortified breads and cereals, can lead deficiencies. Vitamin B₁₂ deficiency can also occur in people who eat a healthy diet. For example, pernicious anemia is an autoimmune disorder that affects dietary uptake of vitamin B₁₂, resulting in vitamin B₁₂ deficiency.

Folate deficiency also leads to megoblastic anemia. In addition, folate is vital during fetal development, thus folate deficiency in pregnant women can lead to neural tube defects in their offspring. In addition to lack of folate in the diet, folate deficiency is also caused by malabsorption of this essential nutrient.

Problems

The student is referred to an excellent module on vitamin B₁₂ and its role in metabolism prepared by Dr. Louise Canfield.

	B12Uptake Animation (3.4MB) Uptake of folate is not treated in detail in this course.