Lecture 12: Micronutrients - Iodine, Selenium & Iron Flashcards
How much is the total body content of iodine, where is the majority of it and what are the bodily functions?
- Total body content is approx 15 to 50mg
- Over 70 to 80% in the thyroid gland
Key role in the body:
- Metabolism of iodine is closely linked to thyroid function
- The only known function for iodine is the synthesis of thyroid hormones (regulate body temperature, metabolic rate)
What are 6 sources of iodine?
- Seaweed
- Iodised salt
- Fish and shellfish
- Milk
- Eggs
- Bread fortified with iodised salt
What do the iodine levels of meat/dairy and fruits/vegetables depend on?
The iodine content of the animal feed or the soil
What does iodine deficiency look like?
- Goitre, enlargement of the thyroid gland due to insufficient iodine, occurs where intakes are less than 50 μg/day
- Cretinism (severely stunted physical and mental growth) occurs where maternal intakes are less than 30 μg/day
Is iodine a major problem in public health?
Yes, the WHO estimates 2 billion people have inadequate iodine nutrition
- ~20 million may suffer mental defect preventable by correction of iodine deficiency
- Major cause is inadequate dietary iodine from foods grown in soils from which iodine has been leached by glaciation, high rainfalls, or flooding
What does the history of iodine deficiency look like in NZ?
Glaciation causes low levels of iodine in the soil
1920s: Goitre widespread in NZ: dressmakers used to make necklines larger to make room for enlarged thyroid glands
1924: Table salt iodised at a low level but little effect
1938: Table salt iodised at 40-80mg/kg goitre rate fell swiftly
1958: Only 0.1% of population had goitre
1960s: Dairy factories using iodine-based sanitizer
1980s: Re-emergence iodine deficiency
- Sanitiser phased out
- Concerns with high salt intake and hypertension
- More highly processed food which doesn’t use iodised salt
- Trend towards non-iodised salts eg sea salt, rock salt
How does one assess the iodine status?
- Urinary iodine excretion;
- Assessment of thyroid size
- Serum level of thyroid hormones
What was a change in NZ that increased the iodine levels of adults and children?
Mandatory iodisation of salt in bread in 2009
What does iodine toxicity look like?
- Excessive intakes cause enlargement of the thyroid gland, hyperthyroidism (if
deficient) and hypothyroidism, autoimmune thyroid disease - Unlikely to occur by consumption of natural foods, unless diet is exceptionally rich in marine fish or seaweed
What are 5 functions of selenium?
- Antioxidant defense
- Thyroid metabolism
- Immune function
- Reproductive function
- DNA synthesis
What are dietary sources of selenium?
- Meat, eggs, diary, bread main sources in NZ
- Seafood and organ meats best source
- Plant sources vary with the geography (reflects selenium content of the soils)
- Some plants (garlic, mushrooms, broccoli) have developed the ability to accumulate selenium from the soils and may contain higher levels of selenium
What does selenium deficiency look like?
- Pure selenium deficiency is rare
- May only occur when low selenium status is linked with additional stress such as vitamin E deficiency (–> minerals working together)
- Low blood selenium values may be associated with:
Immune system
Cancer
Cardiovascular Disease
What does the selenium of NZ soil look like?
- 1950s: White muscle disease in cattle and sheep due to selenium deficiency
- NZ farm animals drenched with selenium-enriched products
- Meal fed to poultry has selenium added
- South Island bread lower in selenium as made from SI wheat
- North Island bread uses more Australian wheat which is selenium rich
Is selenium deficiency a problem in NZ?
- Otago University conducted studies on consequences of selenium status of NZ, metabolism and effects of supplementation
- Selenium intake and status of New Zealanders is low
- BUT: No clinical signs of deficiency
Selenium-iodine interrelationship; selenium is part of thyroid hormone production (–> minerals working together)
What is the main role of fluoride in the body?
Reduces prevalence of dental caries
What are 3 sources of fluoride?
- Beverages, but contribution depends on fluoride concentration of water supply
- Plant foods generally supply more than animal foods
What are the effects of high intake of fluoride?
Dental fluorosis:
- Occurs with too much fluoride during the first 8 years of life
Skeletal fluorosis:
- Occurs with chronic high levels of fluoride intake (water 4-12ppm)
- Causes bone and joint abnormalities
What is the role of iron in the body?
- Iron part of haemoglobin (RBC) and myoglobin (muscles)
- Oxygen transport to lungs and return of CO2 for excretion
- Part of many enzymes, some proteins and compounds important in energy production
- Immunity
- Brain function
- Bone health
What are two kinds of iron?
Haem Iron:
- Derived from haemoglobin and
myoglobin in meat
- Better absorbed and higher bioavailability
Non-haem iron:
- Found in wide variety of plant and animal foods
- Lower bioavailability
What are sources of iron for NZ adults?
- Bread
- Breakfast cereals
- Vegetables
- Grains and pasta
- Beef and veal
What are 2 enhancers and 3 inhibitors of iron absorption?
Enhancers:
- Foods with vitamin C
- MPF factor: meat, poultry, fish
Inhibitors:
- Phytates – found in legumes, wholegrains
- Vegetable proteins: soybeans, legumes, nuts
- Tannins – in tea and coffee
What are 3 factors affecting iron balance?
- Loss: menstruation, bleeding, hookworm
- Requirements: growth, pregnancy, lactation
- Supply: food, type of iron supplied, inhibitors and promoters of bioavailability
What do the 3 stages of iron deficiency look like? And what are the symptoms of mild and severe anaemia?
Stages:
1. Iron stores become depleted (still enough for red cell production)
2. Iron in circulation starts to fall and red cell production becomes compromised
3. Red cell production is drastically reduced and anemia develops
Mild Anaemia: decreased productivity
Severe Anaemia: weakness, impaired effort tolerance, eventual heart failure
–> Most common nutritional disorder, globally 2 billion people, 30% population
What does iron overload look like?
- Excessive amounts may accumulate in body and result in organ damage
- Acute overload: pain, vomiting, metabolic acidosis, cardiovascular collapse and possible death
Haemochromatosis
- Genetic disease increasing iron absorption
- If untreated leads to organ damage esp. liver & heart
- Regular blood donations and avoidance of high iron foods
- ~1/300 people
