Midterm 2 Section 3 Flashcards
micronutrients definition
needed in small (mg/microgram) amounts in the diet
metabolically essential nutrients (not synthesized, perform specific functions, deficiency will result without intake)
why do metals need to be bound?
they are toxic when free
where/how are minerals synthesized?
in the sun or in nuclear reactors
major minerals
minerals in 60kg person
Ca, P, K, S, Na, Cl, Mg
Ca - 1150g, P - 600g, K - 210g, S - 150g, Na - 90g, Cl - 90g, Mg - 30g
Trace minerals
trace minerals in 60kg person
Fe, Zn, Cu, Mn, I, Se
Fe - 2.4g, Zn - 2g, Cu - .09, Mn/I/Se - .02g
electrolyte minerals
Na-K balance, where in cells
K, Na, Cl, Mg
K inside cells, Na outside cells (tears taste salty)
vitamins
vitamers
essential organic micronutrients
different forms of vitamin with different functions and conversion between forms
B vitamins function
examples of functions B1-B6 (no B4)
function as coenzymes in intermediary metabolism
B1 (thiamine) - TTP (thymidine triphosphate) for pyruvate decarboxylation
B2 (riboflavin) - FAD, FMN
B3 (Niacin) - NAD, NADP
B5 (pantothenic acid) - acetyl coA
B6 (pyroxidine, RDA based on protein intake) - PLP in transamination
types of bone
cortical bone - compact bone that makes up the outer surface, and 80% of all bone
trabecular bone - spongy scaffolding bone that makes up 20% of bone and supports cortical bone
examples of trabecular bone: ends of long bones and vertebrae, metabolically active including RBC formation
bone resorption
bone formation
osteoblasts produce
surface of bone is broken down by osteoclasts
osteoblasts synthesize new bone in resorption pits
osteoblasts produce collagen component of bone
osteoporosis
prevalence stats in Canada
degradation of mostly trabecular bone
vertebrae lose bone mass and compress
bones become susceptible to fracture
prevalence: 30% of women, 20% of men
screening for osteoporosis
DEXA scan pre and post menopause as a lot of bone loss happens during this time (20%)
osteoporosis is a pediatric disease
DEXA is low dose radiation and non-invasive
osteopenia vs osteoporosis
T score means
of standard deviations below the mean established for young, healthy population
osteopenia: bone mineral density -1 to -2.5 T score
osteoporosis: bone mineral density >-2.5 T score
number of standard deviations below the mean for young, healthy person
who is most at risk for osteoporosis and why?
women, because 20% bone mass loss during menopause due to decreased estrogen
men have greater bone mass, so bones have more of a buffer
hereditary factors (polygenic, some people absorb less calcium) and lifestyle
caucasians and asians at higher risk
bone health team
players: osteoblasts, osteoclasts, collagen protein, Ca, P, Mg, F
coaches: vitamin D, parathyroid hormone and calcitonin
assistants: vitamins A, C and K
acute functions of Ca
muscle contraction, nerve impulse transmission, blood clotting, immune function, blood pressure moderation
all acute functions are Ca as an ion in solution
must be maintained in precise homeostasis, physiological not diet based
chronic functions of Ca
mineral of bones and teeth
maintains bone turnover
low blood calcium robs bones of calcium to maintain blood homeostasis
causes stunting in children and osteoporosis
tetany
when blood Ca is low, causes muscle tremors
what causes rigor mortis?
When someone dies, ions are no longer pumped, Ca binds myosin and causes muscle contraction
low blood calcium pathway
low blood calcium triggers parathyroid gland releases PTH (parathyroid hormone) which targets the kidneys and bones to release Ca into the blood
Kidneys activate calcitriol
Calcitriol signals kidneys to reabsorb more Ca from urine, increase Ca release from bone into blood, and increase absorption of Ca in the SI
high blood calcium pathway
high blood calcium triggers thyroid gland to produce calcitonin
Calcitonin signals osteoblasts to reuptake calcium into the bones and build bone
why is the RDA difficult to set for Ca?
why is the RDA for pregnant and lactating women the same as the adult RDA?
- genetics affect peak bone density
- dietary intake doesn’t affect the short term affects as much
- pregnant women’s RDA is still 1000mg because hormone changes during pregnancy increase bioavailability during pregnancy and lactation
percent of people that meet the RDA for calcium
90% of people consume 1000mg or less
10% consume the RDA
Good sources of Ca
milk, yogurt, cheddar, tofu set with Ca, sardines
bok choy and broccoli are ok sources but well absorbed
Calcium absorption is increased by
Calcium absorption is decreased by
anabolic hormones, gastric acid, vitamin D, low phosphate intake
aging, low stomach acid, vitamin D deficiency, high phosphate intake, high insoluble fiber intake, high phytate/oxalate intake
bioavailability definition
degree to which a particular nutrient from a food source can be utilized
Foods that decrease Ca bioavailability
why is spinach a poor source of Ca?
insoluble fiber binds cations
phytates: legumes, nuts and cereals
oxalates: spinach, beets, celery, eggplant, okra, berries, nuts, tea and cocoa
spinach is high in Ca but also high in oxalates, so only 5% bioavailability, whereas broccoli is 50% bioavailable
who should take a Ca supplement?
type of supplement recommended
those at risk for low Ca intake like lactose intolerance, vegan or milk allergy
amino acid chelates ($$), Ca-based antacids, calcium citrate/gluconate/malate/carbonate, Ca chews
dolomite/bone meal not recommended due to contamination
multi-minerals can decrease absorption
UL for Ca
side effects of toxicity
UL is 2500mg
milk alkali syndrome - metabolic alkalosis and renal failure
compromised iron and other mineral status
kidney stones
vitamin D toxicity and increased serum Ca if also supplementing vitamin D
contaminants from bone meal supplements
Vitamin D synthesis
cholecalciferol synthesized from cholesterol from 10-15 minutes of summer sun on hands and face (UVB rays)
decreases with age, dark skin, latitude and winter
Foods high in vitamin D
fatty fish, egg yolks, liver, fortified milk
Vitamin D pathway
Provitamin 7-dehydrocholesterol made in the liver from cholesterol
In the skin, ultraviolet light converts 7-dehydrocholesterol into previtamin D3, which is then converted into D3
D3 (calciferol animal food sources), D2 (ergo calciferol, plant sources) from diet
In the liver D3 is hydroxylated into 25-hydroxy vitamin D3 (calcidiol)
In the kidneys D3 is hydroxylated again into 1,25-dihydroxy vitamin D3 (calcitriol) which is the active form
which form of vitamin D can be stored?
calcidiol (the one made in the liver)
Functions of vitamin D
required for calcium and phosphorus absorption
regulates blood Ca
stimulates osteoclasts
stimulates bone calcification
immunity and cell differentiation
*see calcium pathway
vitamin D hormone and vitamin functions
hormone: travels in the blood to be activated in the liver and kidneys, acts on target tissues bone, kidney and intestines, increases Ca availability for bone mineralization and remodeling
vitamin: it is essential in the diet, with deficiency symptoms develop, it performs a specific function, we can’t synthesize as much as we need
RDA vitamin D
assumes inadequate sun exposure
15ug/day or 600 IU per day under 70 years old
Above 70 is 20ug/800 IU
vitamin D toxicity side effects
cannot occur from skin synthesis, only excess supplements/fish oil
hypercalcemia - high blood calcium
leads to calcification of soft tissues, disability and death can occur
UL is 100ug/day (4000 IU)
reasons for high vitamin D deficiency in Canada
winter, reliance on fortification, pregnant milk restricted intake, sunscreen recommendations
Osteomalacia
vitamin D deficiency in adults, intake below 2.5 ug/day
leads to decreased Ca absorption, loss of bone matrix and defective mineralization
decreased bone remodeling and softening of bone
bone pain and hip fracture risk
Rickets
vitamin D deficiency in children
growing bones don’t mineralize properly
softening of bones leads to bowed legs, stunting and teeth problems
prevalence decreased with milk fortification, increasing again due to strictly breastfed babies
Why should babies receive vitamin D supplementation while breastfeeding?
transfer in milk is regulated so it won’t improve child’s uptake if the mother supplements
Phosphorus function in bone
with Ca forms hydroxyapatite mineral of bone
high intake decreases Ca uptake due to competition
typical intake is higher than RDA
Magnesium function in bone
bone structure and regulation of mineralization
vitamin D metabolism
ATP synthesis
other: blood clotting, muscle contraction (opposite of Ca), blood pressure regulation
vitamin K function in bone
co-enzyme for post-translational modification of bone proteins
deficiency results in poorly bound minerals
vitamin A function in bone
bone remodeling
osteoclast activity
vitamin C function in bone
cofactor for collagen synthesis (organic matrix)
best way to prevent osteoporosis
maximizing peak bone mass increases time it takes to get below fracture risk threshold
rate of bone loss per year after 20s to 30s
how to increase peak bone mass
1-2% per year, with increased losses during menopause for women
diet and exercise before the age of 20
after 20, diet, exercise and drugs can slow decline but can’t flatten it
risk factors for osteoporosis
protective factors for osteoporosis
older age, low BMI, caucasian, asian or hispanic, cigarettes, excessive alcohol, glucocorticoids, anticonvulsants, high P, Na and protein intake
younger age, high BMI, African American, weight bearing exercise, diuretics, estrogen therapy, good lifetime diet
how do smoking and alcohol increase risk of osteoporosis?
smoking - associated with low BMI, early menopause, low postmenopausal estrogen, decreased blood flow to bone
alcohol - increased Ca excretion, associated with lower dairy intake, toxic to osteoblasts
