Skills to Develop
- Summarize the role of the B vitamins in blood functions.
- Explain how Vitamin K supports a life-saving function of blood.
In addition to being essential for metabolism, many vitamins and minerals are required for blood renewal and function. At insufficient levels in the diet, these vitamins and minerals impair the health of blood and consequently the delivery of nutrients in and wastes out, amongst its many other functions. In this section, we will focus on the vitamins that take part in metabolism and blood function and renewal.
Vitamins: Functions in Blood
Folate (pteroylglutamic acid)
Folate is a water-soluble vitamin and its primary form is tetrahydrofolate (THF). It is a required coenzyme for the synthesis of the amino acid methionine, and for making RNA and DNA. Therefore, rapidly dividing cells are most affected by folate deficiency. Red blood cells, white blood cells, and platelets are continuously being synthesized in the bone marrow from dividing stem cells. A consequence of folate deficiency is macrocytic, also called megaloblastic, anemia. Macrocytic and megaloblastic mean “big cell,” and anemia refers to fewer red blood cells or red blood cells containing less hemoglobin. Macrocytic anemia is characterized by larger immature red blood cells and fewer mature red blood cells. It is caused by red blood cells being unable to produce DNA and RNA fast enough—cells grow but do not divide, making them large in size.
Figure 10.3.1: Spina bifida is a neural-tube defect that can have severe health consequences.
Folate is especially essential for the growth and specialization of cells of the central nervous system. Children whose mothers were folate-deficient during pregnancy have a higher risk of neural-tube birth defects. Folate deficiency is causally linked to the development of spina bifida, a neural tube defect that occurs when the spine does not completely enclose the spinal cord, and anencephalopathy (no brain). Spina bifida can lead to many physical and mental disabilities (Figure 10.3.1). Observational studies show that the prevalence of neural-tube defects was decreased after the fortification of enriched cereal grain products with folate in 1996 in the United States (and 1998 in Canada) compared to before grain products were fortified with folate (Figure 10.4.3). Additionally, results of clinical trials have demonstrated that neural-tube defects are significantly decreased in the offspring of mothers who began taking folate supplements one month prior to becoming pregnant and throughout the pregnancy. In response to the scientific evidence, the Food and Nutrition Board of the Institute of Medicine (IOM) raised the RDA for folate to 600 micrograms per day for pregnant women. Some were concerned that higher folate intakes may cause colon cancer, however scientific studies refute this hypothesis.
A deficiency in folate can manifest with a variety of different symptoms including mental confusion, headache, glossitis (smooth, red tongue), weakness, fatigue, dyspnea (shortness of breath), and elevated blood levels of homocysteine. Smokers, individuals who consume large amounts of alcohol, oral contraceptive users, pregnant women, infants fed goats' milk, cancer patients receiving some type of chemotherapy, antibiotic users, and chronic consumers of aspirin and antacids are at risk of developing a folate deficiency. Folate can mask a vitamin B12 deficiency.
See Table 10.3.1 for a list of foods rich in folate. Folate is easily destroyed by heat and air, so one should be careful when cooking folate-rich foods. Fresh is best.
Vitamin B12 or cobalamin is water-soluble and the biggest vitamin by weight and size. Cobalamin contains cobalt, making it the only vitamin that contains a metal ion. Cobalamin is an essential part of coenzymes. It is necessary for the maintenance of nerve cells, energy metabolism, hormone production, fat and protein catabolism, for folate coenzyme function (removes methyl group), and for hemoglobin synthesis. An enzyme requiring cobalamin is needed by a folate-dependent enzyme to synthesize DNA. Thus, a deficiency in cobalamin has similar consequences to health as folate deficiency. In children and adults cobalamin deficiency causes macrocytic anemia, and in babies born to cobalamin-deficient mothers, there is an increased risk of neural tube defects.
In order for the human body to absorb cobalamin, the stomach, pancreas, and small intestine must be functioning properly. Cells in the stomach secrete a protein called intrinsic factor that is necessary for cobalamin absorption, which occurs in the small intestine (illeum). Impairment of secretion of this protein either caused by an autoimmune disease or by chronic inflammation of the stomach (such as that occurring in some people with H.pylori infection), can lead to the disease pernicious anemia, a type of macrocytic anemia. Vitamin B12 malabsorption is most common in the elderly, who may have impaired functioning of digestive organs, a normal consequence of aging. Only a small amount of vitamin B12 is absorbed passively without the intrinsic factor complex. Pernicious anemia is treated with large oral doses of vitamin B12 or by putting the vitamin under the tongue, where it is absorbed into the bloodstream without passing through the intestine. In patients that do not respond to oral or sublingual treatment, vitamin B12 is given by injection.
People with stomach dysfunction, vegans and people with bariatric surgery or ileum problems are at risk of developing a vitamin B12 deficiency. It can take up to 20 years for the deficiency to manifest if your dietary intake is inadequate but only 3 to 7 years if you are missing intrinsic factor. Dietary folate can disguise a vitamin B12 deficiency until irreversible neurological problems develop.
A summary of the prominent functions of the folate and vitamin B12 their deficiency syndromes is given in Table 10.3.1.
|B Vitamin||Function||Deficiency: Signs and Symptoms|
|Folate||Coenzyme; amino acid synthesis, RNA, DNA, and red blood cell synthesis||Diarrhea, mouth sores, confusion, anemia, neural tube defects|
|B12 (cobalamin)||Coenzyme; fat and protein catabolism, folate function, red-blood-cell synthesis||Muscle weakness, sore tongue, anemia, nerve damage, neural tube defects|
The USDA has an interactive database of nutrient contents in food. To view reports of single nutrients simply click on the one you are interested in and view the report. http://www.ars.usda.gov/Services/docs.htm?docid=20958
Dietary Sources Rich in Folate and Vitamin B12
To assist you in getting all the folate you need to support blood cell synthesis look over Table 10.3.2 for good dietary sources of these micronutrients. Fifty to ninety percent of folate in foods can be destroyed by food processing and preparation, unltraviolet light, and oxidation.
Vitamin B12 is produced by the bacteria in your gut and you can find it in fermented foods, nutritional yeast, and soil contaminants. Foods tend to be a secondary source of vitamin B12 with gut microbes being the primary source. A list of foods considered good sources of vitamin B12 are shown in Table 10.3.3.
|Food||Micrograms per Serving||Percent Daily Value|
|Liver||185 (3 oz.)||45|
|Calf liver||650 (3 oz.)||160|
|Fortified breakfast cereals||400 (¾ c.)||100|
|Spinach||100 (½ c., boiled)||25|
|Northern beans||100 (½ c., boiled)||25|
|Asparagus||85 (4 spears, boiled)||20|
|Vegetarian baked beans||60 (1 c.)||15|
|Broccoli||45 (2 spears)||10|
|Avocado||45 (½ c.)||10|
|Bread (enriched)||25 (1 slice)||6|
Source: National Institutes of Health, Office of Dietary Supplements. “Dietary Supplement Fact Sheet: Folate.” Last reviewed April 15, 2009. http://ods.od.nih.gov/factsheets/Folate-HealthProfessional/.
|Food||Micrograms per Serving||Percent Daily Value|
|Liver||48 (1 slice)||800|
|Clams||34.2 (3 oz.)||570|
|Organic calf liver||31 (3 oz.)||520|
|Fortified breakfast cereals||6.0 (1 serving)||100|
|Trout (wild)||5.4 (3 oz.)||90|
|Trout (farmed)||3.5 (3 oz.)||58|
|Salmon (sockeye)||4.8 (3 oz.)||80|
|Yogurt (plain)||1.4 (1 c.)||23|
|Beef (top sirloin)||1.4 (3 oz.)||23|
|Milk||0.9 (1 c.)||15|
|Egg||0.6 (1 large)||10|
Source: National Institutes of Health, Office of Dietary Supplements. “Dietary Supplement Fact Sheet: Vitamin B12.” Last reviewed June 24, 2011. http://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/.
Vitamin K: Functions in Blood
Vitamin K is a fat-soluble vitamin that is critical for the formation of the blood clotting factors, thrombin, and fibrin. Blood-clotting proteins are continuously circulating in the blood. Upon injury to a blood vessel, platelets stick to the wound forming a plug. The clotting factors circulating close by responding in a series of protein-protein interactions resulting in the formation of the fibrous protein, fibrin, which reinforces the platelet plug (Video 10.3.2) for an animation of the blood-clotting cascade of events). Vitamin K is also needed for the formation of the bone matrix proteins osteocalcin and matrix Gla.
Video 10.3.1: How Does Blood Clot? This video gives a brief description of the blood-clotting process (click to see video).
A deficiency in vitamin K causes bleeding disorders. It is relatively rare, but people who have liver or pancreatic disease, celiac disease, or malabsorption conditions are at higher risk for vitamin K deficiency. Signs and symptoms include nosebleeds, easy bruising, broken blood vessels, bleeding gums, and heavy menstrual bleeding in women. The function of the anticoagulant drug warfarin is impaired by excess vitamin K intake from supplements. Calcium additionally plays a role in activation of blood-clotting proteins as discussed in the previous chapter. Vitamin K also plays a role in bone mineralization and a deficiency in this vitamin prevents bone mineralization. People who have fat malabsorption, some infants at birth, and people taking a large amount of non-absorbable antibiotics for a long time are at risk of developing a deficiency.
The rat poison, Warfarin, blocks blood clotting by inhibiting vitamin K. It is used to treat strokes and heart attacks. If one's vitamin K intake is high, this reduces the effectiveness of these drugs. Fluorescent light and sunlight destroy vitamin K.
Dietary Reference Intakes and Sources of Vitamin K
The RDA for vitamin K for adult males is 120 mcg/day and for adult females is 90 mcg/day. Vitamin K is present in many foods and most highly concentrated in green leafy vegetables. See Table 10.3.4 for a list of dietary sources of vitamin K. Bacteria in our large intestine synthesize vitamin K.
|Food||Micrograms per Serving||Percent Daily Value|
|Broccoli (½ c.)||160.0||133|
|Asparagus (4 spears)||34.0||28|
|Cabbage (½ c.)||56.0||47|
|Spinach (½ c.)||27.0||23|
|Green peas (½ c.)||16.0||13|
|Cheese (1 oz.)||10.0||8|
|Ham (3 oz.)||13.0||11|
|Ground beef (3 oz.)||6.0||5|
- The water-soluble B vitamins are involved as coenzymes in the breakdown of nutrients and in the building of macromolecules, such as protein, RNA, and DNA.
- B-vitamin deficiencies are relatively rare especially in developed countries; although the health consequences can be severe as with folate deficiency during pregnancy and the increased risk of neural-tube defects in offspring.
- Vitamin K is necessary for blood clotting.
- Discuss how the actions of B vitamins are interdependent; meaning the level of one affects the function of another.
- Have a classroom debate on whether it is prudent for the federal government to regulate claims on micronutrient supplements, such as those containing B vitamins.