(8/18/10) - Intro to Micronutrients

Unless otherwise noted, these answers came out of the lecture notes Dr. Noramly posted to the website.

Vitamins, Minerals and Antioxidants
1. Define the dietary terms: vitamin, mineral, antioxidant. List the classifications of vitamins. Distinguish between the terms: macrominerals, microminerals, and trace elements.

Vitamins
Vitamins are organic compounds required in small quantities in the diet for the maintenance of proper health. They play key roles as cofactors in metabolic reactions, or regulators of certain processes such as differentiation.

The two main classes are water-soluble vitamins (C and B-complex), which must be consumed everyday, and lipid-soluble vitamins (DEAK), which are stored in the body and so do not need to be consumed daily.

Minerals
Mineral are inorganic substances. Not all have established roles in health maintenance. They can be stored in the body, so deficiencies are rare.

Macrominerals include calcium, chloride, phosphorous, potassium, sodium. They make up a relatively large percentage of the body's weight.

Microminerals include copper, fluoride, iodide, selenium, zinc, etc. They make up a relatively small percentage of the body's weight. They are also referred to as trace elements.

Antioxidants
Antioxidants prevent oxidative injury to the body's organs and molecules due to the action of free radicals. They function by being so easily oxidized themselves, and thus spare the molecules in the body from that fate. These can be either minerals or vitamins, or neither, and include vitamin C, vitamin E, beta-carotene, and selenium.

Vitamin Stability, Solubility, Transport, and Role in Metabolism
2. For the following vitamins relate the essential structural features of each vitamin to its stability, lipid solubility, transport, coenzyme form, and role in metabolism: Vitamin C, Vitamin D, Vitamin K, Vitamin B12, thiamine, folic acid (Note: this is a long-term goal and may take many curricular weeks). Know the key symptoms of their deficiency and explain their cause.

· Vit C: Water-soluble (not stored, excreted)

o Helps Ý iron absorption, anti-oxidant, resistance to infection, hormone synthesis, form collagen

· Vit D: Fat soluble (stored)

o Necessary for absorption of calcium (increases membrane permeability, induces synthesis of calbindin) o Functions as hormone in absorption of calcium & phosphorus; mobilization & mineralization of bone

· Vit K: fat soluble; synthesized in livers o Forms prothrombin for blood clothing o Large amounts are toxic

· Thiamine: water soluble o Co-enzyme for breakdown of glucose for energy o Necessary for: nerves, digestion, appetite, good mental outlook

· Folic acid: water soluble; involved in RBC maturation; fruits and vegetables contain polyglutamyl folate that is converted to folic acid at brush border

· Vit B12: water soluble

1. Gastric acid and pepsin cause release of vitamin B12 from food 2. VitB12 binds cobalophilin (from saliva). 3. In duodenum, cobalophin is hydrolyzed. 4. VitB12 then binds to intrinsic factor (secreted by parietal cells) 5. VitB12 + intrinsic factor is absorbed in distal ileum o Formation of mature RBC

· VitC deficiency: Poor wound healing, poor tooth/bone development, scurvy (bruising & hemorrhage, bleeding gums, lose teeth); GI problems, osmotic diarrhea

· VitD deficiency: Functions as hormone in absorption of calcium & phosphorus; mobilization & mineralization of bone

· VitK deficiency: prolonged clotting time, hemorrhage

· VitB12 defiency: anemia, glossitis, cheilosis, paresthesias, ataxia

· Thiamine deficiency: Beriberi, fatigue, ß appetite, depression, neuropathy, edema, angular stomatitis, etc.

· Folic acid deficiency: pallor, macrocytic anemia in pregnancy, sprue, pallor

Absorption, Transportation, Storage, and Turnover of Minerals
3. For the following minerals required in the human diet, explain how each is absorbed, transported, and stored and how its turnover is regulated: Iron and calcium. (Note: this is a long-term goal and may take many curricular weeks). Know the key symptoms of their deficiency and explain their cause.

Micronutrient Absorption and Bioavailability
4. Describe factors influencing micronutrient absorption and bioavailability.

Bioavailability refers to the access of a dietary nutrient to its tissue target. This depends on nutrient form, digestion and absorption (disorders), transport (recognition by carrier proteins), uptake by target tissue, and interfering substances (such as fiber). For instance, calcium, iron, and zinc are more likely to be absorbed in the presence of vitamin C, Heme iron (iron present in meats) is more readily absorbed than non-heme iron (iron present in vegetables), and calcium citrate is more bioavailable than calcium carbonate.

Intake differing from DRI
5. Explain how a daily vitamin or mineral intake that is greater than or less than the DRI causes common clinical symptoms or pathology. Be cognizant of the dangers of certain supplement

practices.

See Table 2 in Dr. Noramly's Lecture Notes.

An excess of Vitamin A during pregnancy can result in birth defects. Excess vitamin C over an extended period of time may result in urinary tract pathologies due to the long-term acidification of urine. A high zinc intake can decrease copper status; iron can hinder absorption of some antibiotics, vitamin E can cause bleeding problems. Significant toxicity has been identified with excess consumption of vitamin D.

RDA, DRI, AI, EAR, and UL (or, a lot of acronyms)
7. Define Recommended Dietary Allowance (RDA), Dietary Reference Intake (DRI), Adequate Intake (AI), Estimated Average Requirement (EAR); and Upper Limit (UL); explain how these values are established for different age/gender groups; and identify the population groups to which they apply.

Recommended Dietary/Daily Allowance (RDA)
The dietary intake level that is sufficient to meet the nutrient requirement of nearly all healthy individuals in a particular life stage and gender group on a daily basis.

Dietary Reference Intake (DRI)
Guidelines for the amounts of nutrients needed to maintain overall health by the Institute of Medicine.

Adequate Intake (AI)
Recommended intake value used when RDA is not set for a nutrient, based on experimentally derived levels of intake, or the mean intake by a group of apparently healthy people.

Estimated Average Requirement (EAR)
Intake value at which 50% of an age and gender specific group would not have its requirements fulfilled (i.e. the amount required for 50% of a given population to maintain health).

Upper Limit (UL)
The highest level or usual intake that is not likely to pose risk of adverse health effects for nearly all individuals in the age and gender group.

Micronutrient Deficiencies in Populations
8. Identify types of individuals, populations or communities at risk for specific or general dietary vitamin and mineral deficiencies or imbalances as a result of genetic, environmental, or sociocultural influences. In pregnant women, potential nutrition problems include insufficient folate, B12 and B6, which could cause fetal neural tube defects, and iron, which can cause maternal anemia and failure to build up fetal iron stores.

Premature infants do not have adequate iron stores and are at risk for anemia. All infants should receive vitamin K at birth to prevent severe bleeding. Older infants may need more iron and vitamin D may be a problem for some breastfed infants.

Teenagers may take supplements to change weight or body compositions. They also need to ensure they have adequate calcium as it can indicate bone health later in life.

Older adults (older than 65) need to ensure they have adequate calcium, vitamin D, and B12 intake. Low levels of calcium and Vitamin D can put these individuals at a higher risk for osteoporosis and bone fractures. A low B12intake leads to polyneuropathy and mental impairment.

Vegans and other vegetarians may be at risk for some vitamin and mineral deficiencies due to low intake.

Those with a generally low intake of food (whether because of socioeconomic reasons or due to eating disorders) should take a supplement, as should alcoholics (as alcohol can interfere with absorption of B-complex vitamins), as should physically or mentally challenged individuals.