Lecture 11: Micronutrients - Vitamins A, C & E and Vegetables Flashcards
What are 2 forms of vitamin A?
-
Retinol – pre-formed vitamin A
- Sources include: liver, fish liver oil, eggs and dairy products -
Carotenoids – pro vitamin A (pigments in fruit and veg many of which are antioxidants)
- Sources include: spinach, carrots, red and green capsicum, other leafy green vegetables
What are the 5 main functions of vitamin A?
- vision (retinol helps the eye adjust to dim and bright lights)
- protein synthesis and cell differentiation
- cell growth, reproduction and development including at DNA level
- immunity; production of white blood cells
- important antioxidant (CVD and cancer prevention)
How is the vitamin A consumption among NZ adults and why? And how does it look in different age groups?
NZ adults are not consuming enough to meet the RDI, largely because they do not eat enough veggies.
There is a trend where vitamin A consumption gradually goes up from younger to older age groups.
What are symptoms of vitamin A deficiency?
- Night blindness
- Corneal drying
- Bitot’s spots
- Build up of keratin
- Macular degeneration and blindness; damages sharp and central vision
- Impaired immunity, e.g. assists in preventing infectious diseases
What does vitamin A deficiency look like?
- Fat soluble vitamin, stored in the liver
- Symptoms include: birth defects, liver abnormalities, osteoporosis, hair loss, dry skin
- Not common result of food consumption, most cases result from supplement use
What are some sources of vitamin C?
- Brussel sprouts
- Red capsicum, raw
- Red capsicum, cooked
- Kiwi fruit
- Orange, raw
- Broccoli, cooked
- Broccoli, raw
Why are raw vegetables/fruits a better source of vitamin C?
Because vitamin C is water soluble and therefore disappears more when the vegetables are cooked
What are the 5 main functions of vitamin C in the body?
- Synthesis of collagen; healthy bones, teeth, tendons, blood vessels, scar tissue
- Antioxidant
- Vital for good immune function, strengthens resistance to infection
- Enhances absorption of non-haem iron when consumed in the same meal
- Inhibits the conversion of nitrates into carcinogenic compounds (eg in processed meat)
How is the vitamin C intake in NZ adults?
Good, people are meeting the requirements
What do vitamin C deficiency and toxicity look like?
Deficiency
Scurvy:
- Symptoms include: weakness, fatigue, bleeding gums, impaired wound healing, skin hemorrhages, depression
- Uncommon in populations unless prolonged shortage of fruits and vegetables together with overall reduced food supply
Toxicity = low because it is water soluble so any excess will just leave the body through fluids
What is the role of vitamin C in the common cold?
Vitamin C cannot reduce the incidence of colds but it can reduce the duration and severity
What 4 forms of vitamin E are there, and which ones are more common?
- alpha
- beta
- gamma
- delta
Alpha is most common, alpha and gamma’s main form is in foods
–> bioavailability of each form varies
–> fat soluble
What are dietary sources of vitamin E?
- Sunflower oil
- Safflower oil
- Tomato paste
- Pine nuts
- Peanut butter
- Avocado
- Spinach, cooked
- Cashew nuts
What are the 3 main functions of vitamin E?
- Antioxidant; reduces oxidation of lipid membranes
- Protects cells, muscles and tissues from free radical damage
- Cancer, stroke, heart disease, respiratory disease prevention; real food sources likely to be best
What are symptoms of vitamin E deficiency and toxicity?
Deficiency:
- Loss of red blood cells
- Adrenal gland malfunction
- Neurological problems due to poor nerve conduction
Toxicity:
- Rare
- Symptoms: headache, nausea, blurred vision
- Can cause hemorrhage as interferes with Vit K’s blood clotting mechanism – those who are Vit K deficient or taking aspirin most at risk
What do studies say about the consumption of fruits and vegetables and the results?
- Higher consumption of fruit and veg = lower risk all cause
mortality - Higher consumption of fruit and veg = lower risk CHD,
CVD, cancer, all cause mortality
What is the WHO recommendation for consumption of vegetables?
Eat at least 400g (five portions) of fruit and vegetables per day
When should we take supplements?
For:
- Correct deficiencies (B12 if vegan)
- Support increased nutrient needs (folate in pregnancy)
- Improve the body’s defences (Vit C common cold)
- Reduce disease risks
Against:
- Toxicity
- Life-threatening misinformation (treat cancer)
- Unknown needs (may not be
deficient)
- False sense of security (easier than having healthy diet
- Cost
What are free radicals?
= atoms or molecules that are highly reactive with other cellular structures because they contain unpaired electrons
- Natural by-products of biochemical reactions in body
- Can cause damage to parts of cells be stealing electrons through oxidation
- Antioxidants (free radical scavengers) reduce the formation of free radicals or neutralize them
- Vitamins and other substances (eg phytochemicals) can act as antioxidants, but if consumed in large amounts can be free radicals
What do studies say about the use of dietary supplements?
Study 1:
- Ever-use of dietary supplements not associated with mortality outcome
- Adequate intake of Vit A, K associated with reduced all-cause or CVD mortality (nutrient intake from food)
Study 2:
- Antioxidant supplements increased mortality (beta-carotene, vitamin E), high dose of vitamin A
