Lecture 6 and 7 - Calcium and Vitamin D Flashcards
in 1920’s what was the cure that was found for rickets
UV light and cod liver oil
what is the main source of vitamin D
the sun
other sources of vitamin D
- cod liver oil
- sardines
- smoked salmon
- eel
- fortified soy milk
how many times the RDI of vitamin D does one teaspoon of cod liver oil supply
2 times the RDI
Is NZ dairy fortified with vitamin D
very rarely
how does sunlight provide our bodies with vitamin D
UVB light comes through the skin goes through a non enzymatic reaction, causes 7-dehydrocholesterol to form vitamin D3
(action of the sun on the skin does this)
what is shortest wave length of sunlight
UVC
what sunlight wavelength has the largest affect on the top layer of the skin and what does it cause
UVB - causes burning / redness / skin cancer
why is UBV both problematic and useful
has the most use to us but also causes burning / skin cancer
what is the longest wavelength of sunlight
UVA = reaches deep into the layers of skin causing aging and wrinkling
what are the behavioural factors that affect vitamin D status
- clothing (blocks UVB)
- sunscreen
- time of the day
- time spent outdoors
- supplements
- diet (smaller effect as few foods contain vitamin D)
what are host related factors that affect vitamin D status
- skin colour
- age
- sex
- BMI
- genetic differences in vitamin D binding protein and receptors
how does age affect vitamin D status
as you get older, your skin is going to have less of the 7-dehydrocholesterol in it, that means lower ability to form vitamin D
how does sex affect vitamin D status
in high income countries, men tend to have higher levels than women
how does BMI affect vitamin D status
people who are overweight or obese have less circulation vitamin D as it is a fat soluble vitamin (it gets sequested into adipose tissue)
what is melanin
gives the skin, eyes and hair dark colour is the natural protection against the harmful effects of UV light
what are the environmental factors that affect vitamin D status
- season
- latitude
- altitude
- clouds
- atmospheric pollution
what are the two major forms of vitamin D
D2 and D3
where do you get vitamin D3
from animals
what type of vitamin D does the skin make when exposed to UV light
D3
what is the longer name for vitamin D3
cholecalciferol
how is vitamin D3 formed
beta ring on 7-dehydrocholesterol is broken by UVB light, this forms pre vitamin D3, then heat converts that to vitamin D3
what does vitamin D2 start out as and how is it converted to D2
starts out as ergosterol, B ring is broken down by UVB light, pre vitamin D2 is produced, then heat turns it to vitamin D2
what is the longer name for vitamin D2
ergocalciferol
what is the difference between vitamin D3 and D2 in terms of binding affinity and what does this mean
vitamin D2 has lower affinity for the vitamin D binding protein, so therefore cleared faster from the circulation
which is more effective, D2 or D3
D3
vitamin D is a fat soluble vitamin, so therefore what is needed for it to be absorbed
requires fat so it can be absorbed
what are mixed micelles and why is this important
vitamin D is soluble in the hydrophobic core of micelle, phospholipids and bile acids surround it
what do bile acids on the outside of a micelle do
make the micelle soluble in the hydrophilic gut lumen
once absorbed in the upper small intestine, where is vitamin D transported to
transported from the small intestine to the liver by vitamin D binding globulin
is the vitamin D from our food or skin biologically active, what does it require
no, it requires metabolic activation in the body
how is vitamin D metabolic activated (what happens in the liver then where is this transported to and what happens here )
in the liver D3 or D2 will be converted to 25-hydroxyvitamin D (calcidiol)
calcidiol is transported from the liver to the kidney
in the kidney, calcidiol will be converted to 1,25 dihydroxyvitamin D
calcitriol is used as a biomarker of what status
vitamin D levels
what is the active form of vitamin D
calcitriol
vitamin D floating around your body will be in what form, and if something needs to be done what form will it be in
calcidiol = floating round
calcitriol = activated when needed
what is the % of vitamin D deficiency in NZ
5%
where is vitamin D deficiency lowest in NZ
Northern regions
what is rickets
softening of the bones which can lead to fractures and deformity
what is heliotherapy
sun therapy
what is osteomalacia (younger + older adults)
softening of the bones
younger adults = bowing of bones
older adults = fractures
what is the pain associated with osteomalacia
dull aching bone pain, not relieved by rest
what is osteoid
the bone protein matrix (primarily collagen)
in rickets or osteomalacia what happens to osteoid and why
insufficient mineral > the osteoid does not mineralise properly > unmineralized osteoid accumulates
what is the non bone effect of vitamin D
1,25(OH)2D (calcitriol) is the ligand for the vitamin D receptor found in nearly every tissue, controlling hundreds of genes
what could lead to vitamin D toxicity
supplement / fortification errors
what are the non specific symptoms of vitamin D toxicity
anorexia, nausea, vomiting, weakness, changes in mental state
what are the symptoms of vitamin D toxicity related to high blood calcium levels
high blood calcium levels > vascular and tissue calcification > damage to the heart and kidneys : may be fatal
when does bioavailability of calcium decrease
decrease with age
what is the bioavailability of calcium in dairy products
~30%
what is the bioavailability of calcium in kale in fortified soy milk
~20-30%
what is the bioavailability of calcium in kale
~40%
what foods decrease the bioavailability of calcium
foods rich in oxalic acid or phytate
what are the two mechanisms of calcium absorption
absorption by active active transport = requires vitamin D
passive diffusion = increasingly important as Ca intakes increase
for the body to function the serum calcium must be within the narrow range of …
2.12-2.62nmol/L
what maintains the serum calcium levels
levels maintained through an endocrine system with strict controlling factors and feedback mechanisms
(calcitriol and parathyroid hormone play key roles in this)
drop in calcium levels in the blood stimulates what
parathyroid gland to release PTH
in response to PTH release, what will happen
calcium released from the bones will increase
and
calcium uptake in the kidneys will decrease
and
stimulate calcitrol to be released from the kidneys
what will release of calcitriol cause
the calcium in the intestines will have increased absorption
how does negative feedback associated with calcium and PTH work
as calcium levels increase in the blood, your PTH levels begin to drop
if calcium levels get too high what will be increased from the thyroid gland
calcitonin is released which will block the bone calcium absorption
almost 98% of the total body calcium is found where and in what form
as calcium hydroxyapatite in bones and teeth
the other 2% of total body calcium is critical for what
- vascular contraction and vasodilation
- muscle function
- nerve transmission
- intracellular signalling
- hormone secretion
what is reduced bone strength
osteoporosis
calcium deficiency can be hypocalcaemia, what can this also be caused by
usually due to vitamin D or magnesium deficiency or hypoparathyroidism (underperforming parathyroid glands)
what are the wide range of symptoms associated with hypocalcaemia
perioral numbness, tingling hands and feet, muscle spasms
renal and brain calcification, depression, heart failure, seizures, coma
how common is calcium toxicity
rare in healthy people
calcium toxicity is usually a result of
cancer
primary hyperparathyroidism
what does calcium toxicity result in
poor muscle tone
renal insufficiency
constipation
nausea
weight loss
fatigue
higher risk CVD mortality
actions of 1,25(OH)2D - calcitriol
- promotes intestinal absorption of calcium and phosphate
- increases calcium reabsorption from kidney
- direct action of cartilage and bone to promote normal skeletal development and turnover
- inhibits PTH
thinning of bone mass is due to imbalance in what
imbalance in bone resorption and formation
clinical trials show what about vitamin D supplements and cardiovascular disease
“overall, clinical trials show that vitamin D supplementation does not reduce CVD risk, even for people with low vitamin D status”
what is the AI of vitamin D for men and women (also over 50 and over 70 years
5 ug/day
> 50 yrs = 10ug/day
70yrs = 15ug/day
RDI of calcium for men
1,000mg/day
RDI of calcium for women
1,000mg/day
