Lecture 8: Micronutrient - Vitamins B & K Flashcards
What are vitamins and what are two forms of them?
= Vitamins are organic substances which are sensitive to heat, UV light, and oxygen.
- water soluble (B group & C)
- fat soluble (A, D, E, K)
Explain bioavailability
= Refers to the rate at which, or extent to which, a nutrient is absorbed and used by the
body. Can be influenced by cooking methods, the food matrix, and nutrient-nutrient interactions.
What are 3 possible relationships between dose levels and effect for vitamins
- More = better; Better effects with greater intakes, with no end in sight (hardly ever like this!)
- More –> better –> plateau; Effect reaches a maximum with greater intakes, followed by a plateau.
-
More = better until max, then worse; The effect reaches an optimum at an intermediate dose, and then declines. More is better up to a point and then harmful.
Represents the dose-response effect for most nutrients.
What are 8 B vitamins and their general function and other (if special) and source?
-
B1 - Thiamin
Source: Wholegrains, vegetables -
B2 - Riboflavin
Source: Dairy, wholegrain, vegetables -
B3 - Nicotinic acid
Function: Protein and fat synthesis
Source: Widespread -
B5 - pantothenic acid
Source: Vegetables, widespread -
B6 - Pyridoxine
Function: Nervous system acitivity
Source: Widespread -
B7 - Biotin
Source: Vegetables, meat, eggs -
B9 - Folate
Function: DNA synthesis
Source: Wholegrains, vegetables, supplemental -
B12 - Cobalamin
Function: DNA synthesis
Source: Dairy, meat, only in animal-based foods
What is the function of B vitamins in metabolic processes?
Metabolic reactions require enzymes, which need ‘enzyme helpers’ called coenzymes. B vitamins serve as coenzymes in energy metabolism, but do not provide energy themselves.
What does B group vitamin deficiency look like?
- Usually results from inadequate intakes, and tend to occur in groups not isolation.
- Classical deficiency diseases are very rare in high income countries today, as most B vitamins are spread widely throughout the food supply.
At-risk populations include those living in poverty, those with poor-quality food choices, or those with restricted energy intake (e.g., older adults). - Alcoholism increases the risk of B vitamin deficiencies. Alcohol can displace food, AND we use more B vitamins in metabolising alcohol.
What does B group vitamin toxicity look like?
- B group vitamins are water soluble, which means that toxicity is not particularly common.
- Toxicity can result from high doses of niacin (flushes) and pyridoxine (nerve damage) through supplements not food.
Explain Pellagra
= Deficiency disease associated with Niacin, which has widespread roles in energy metabolism.
- 4Ds - Dermatitis, Diarrhoea, Dementia, Death
- Major problem in early 1900s, and many thought that Pellagra was caused by an infectious agent
- Historically appeared in places where maize was the dominant food crop. Niacin in corn is NOT bioavailable.
- Widespread fortification followed, and Pellagra is now a disease of the past.
- Soaking ground maize in an alkaline solution (e.g., lime) water makes niacin bioavailable. This is why some populations were protected from Pellagra, even with corn as a staple of the diet!
Explain the vitamin interaction between folate and B12
Folate and vitamin B12 are inter-dependent - folate needs vitamin B12 for its activation and vice versa. This means that a deficiency in one will exacerbate a deficiency in the other.
Explain folate deficiency
- Folate deficiency is one of the most wide-spread micronutrient deficiencies around the globe. Unlike some other micronutrient deficiencies, this is still a problem in many high income countries.
- Folate deficiency can lead to megaloblastic anemia. Without folate, DNA damage destroys RBCs as they attempt to divide and mature.
- Long-term suboptimal folate intake can also lead to cardiovascular diseases and cognitive impairment. This is a global issue for ageing populations.
Explain B12 deficiency
- Vitamin B12 deficiency is often caused by inadequate absorption (pernicious anemia), not inadequate intakes. The main reasons are;
1. A lack of hydrochloric acid (cannot be released from food)
2. Inadequate intrinsic factor (cannot be absorbed) - Vitamin B12 also plays an important role in DNA synthesis and repair. Like folate, vitamin B12 deficiency can cause megaloblastic anemia.
In what two main forms do vitamin K come?
- K1: green leafy vegetables, soy/canola oil, carrots, pumpkin
- K2: microbial production, egg yolks, full-fat dairy, meat
What is the main function of vitamin K?
Activate proteins:
- Activate blood clotting factors
- Activate proteins which enable calcium to bind to bone, muscle and kidneys
What happens when there is a vitamin K deficiency and what is a population that can be at risk?
Deficiency: bleeding disorders, bruising, hip fractures
–> not very common, diets are usually assumed to have an abundance
At risk population: newborns, surgical patients, long-term fat malabsorption, long-term antibiotic use
What are the recommendations considering the intake of thiamin?
They are based on thiamine role in enzyme activity; generally, thiamin needs will be met if a person eats enough nutritious foods to meet energy needs
Explain beriberi
= Thiamin deficiency
Two versions:
- Dry beriberi = reflects damage to the nervous system and is characterised by muscle weakness in the arms and legs
- Wet beriberi = reflects damage to the cardiovascular system and is characterised by dilated blood vessels, which cause the heart to work harder and the kidneys to retain salt and water, resulting oedema
–> typically the two forms appear together
Explain niacin flush
= Niacin toxicity: occurs when nicotinic acid is taken in doses only three to four times the RDI, it dilates the capillaries and causes a tingling sensation that can be painful
What is the secretion that vitamin B12 binds to called?
Intrinsic factor
What are the recommendations considering the intake of vitamin B12?
2.4 micrograms a day (two-millionths of a gram)
Who are more likely to develop vitamin B12 deficiency and what does that look like/what is it called?
Adults using heartburn medications to suppress gastric acid production and older adults.
Many people, especially those over 50, develop atrophic gastritis, a common condition that damages the cells of the stomach. Without healthy stomach cells the production of hydrochloric acid and intrinsic factor diminishes. The vitamin B12 deficiency caused by atrophic gastritis and a lack of intrinsic factor is called pernicious anaemia.
Vitamin B12 is also required to convert folate into its active form, so anaemia of folate deficiency can also occur, characterised by large immature red blood cells, indicating slow DNA synthesis and inability to divide.
