Vitamin D

Question 1

Calcium and vitamin D

Answer 1

increased intake during rapid bone growth increases peak bone mass -> more complicated than this

Question 2

Higher calcium intakes

Answer 2

increased incidence of hip fractures

Question 3

Low calcium intake and less from milk

Answer 3

less osteoporosis and fewer fractures

Question 4

Adaptation hypothesis

Answer 4

dietary calcium intake above a minimum low level is unimportant as a regulator of bone health -> since plasma free calcium is regulated so finely, adaptive mechanisms exist to maintain calcium balance over a wide range -> because societies with low calcium intakes have low levels of osteoporosis -> OTHER dietary factors and physical activity are more important

Question 5

Plasma Ca concentration

Answer 5

highly regulated by Vitamin D and PTH -> calcitriol (active vitamin D) and PTH act to maintain plasma Ca at a supersaturating level with respect to bone mineral and to prevent hypocalcemic neuromuscular tetany

Question 6

Adaptive responses to low calcium intakes

Answer 6

reduction in plasma Ca -> increased PTH secretion -> increased active vitamin D, increased Ca absorption (both add to increased Ca absorption), decreased urinary calcium and increased conservation of dietary calcium (both lead to reduced calcium loss) -> all lead to the restoration of normal plasma calcium

Question 7

Low intakes of dietary calcium

Answer 7

Very low intakes can cause rickets without vitamin D deficiency

Question 8

Rickets (with normal vitamin D)

Answer 8

low dietary calcium intake, high phytate and oxalate, genetics -> inadequate calcium for absorption to meet needs for skeletal growth -> decreased plasma calcium, increased serum PTH -> increased mineralization defect (hyperosteoidosis) -> rickets and osteomalacia

Question 9

Calcium

Answer 9

Adequate amounts are needed for peak bone mass (PMB) development, diets low in this are also low in other respects

Question 10

Extra calcium

Answer 10

reduces bone mass loss -> proven to aid with bone mineral density -> beneficial in post-menopausal women (milk is better than supplements)

Question 11

Fruit and vegetables

Answer 11

important for bone health -> provide alkali to neutralize dietary acid -> as people age the ability to excrete acid declines and they become more acidic

Question 12

Bone mineral balance

Answer 12

extremely sensitive to acid base balance with demineralization occurring as pH drops below a critical point -> dietary acid and PO4+3 can be buffered by fruits and vegetables (K+ salts of bicarbonate and weak organic acids) -> cheese and meat are high in renal acid loads, fruits and vegetables are negative

Question 13

Osteoclast resorption

Answer 13

increases with increasing acidity

Question 14

K+ and HCO3-

Answer 14

markedly reduced in present day diet -> now Na and Cl -> used to have high diet in this -> supplementation improves calcium and PO4 balance (as does carbonated mineral water)

Question 15

DASH (dietary approaches to stop hypertension)

Answer 15

high in fruits and vegetables and low-fat dairy products, reported improved calcium balance

Question 16

Ca citrate/malate

Answer 16

supplements supplies alkali and this may be a part of their effectiveness for bone health (might have nothing to do with the minerals and more with alkaline pH)

Question 17

Vitamin D how does it regulate Ca and PO4

Answer 17

regulates calcium and PO4 homeostasis -> from sun UVB to skin or from diet -> 25 hydroxylase takes D2 and D3 to 25-OH vitamin D (measure of status -> tissue supply) in the liver -> 1alpha hydroxylase in the kidney hydrolyzes it to 1,25 (OH)2D4 (active hormone)

Question 18

Vitamin D how does it influence Ca PO4

Answer 18

influences calcium-phosphate homeostasis -> in the intestine it increases Ca absorption, in bone it causes Ca release, in kidney it causes Ca retention -> increase free Ca

Question 19

25-OH vitamin D

Answer 19

tissue supply of vitamin D -> can become active form in tissues other than the kidneys -> immune system, CV system, muscle/cartilage, adipose, liver, pancreas, brain, lung, skein, breast, ovary, uterus, placenta, prostate, testes -> 5 % of all human genes have a response element for this

Question 20

Where do you get vitamin D

Answer 20

exogenous hormone -> main source is sunlight (don’t get much in the diet -> high in oily fish, fish oils and some added in dairy and fortified cereals)

Question 21

Vitamin D deficiency

Answer 21

at risk infants, pregnant women, elderly, ethnic minorities in temperate countries, those with limited sun exposure -> rickets in children and osteomalacia in adults

Question 22

Cut off for rickets <25nmol/L

Answer 22

25% deficient for several age groups -> infants, children, pregnant women and elderly

Question 23

Cut off for deficiency in most clinical labs

Answer 23

50% deficient for several age groups (people of all ages)

Question 24

Causes of vitamin D deficiency

Answer 24

reduced skin synthesis (sunscreen use, skin pigment decreased, aging, season, latitude, time of day), decreased bioavailability (fat malabsorption, obesity), increased catabolism (anticonvulsants, glucocorticoids, HAART AIDs treatment, anti-rejection medicines), decreased synthesis (liver failure/dysfunction, nephrotic syndrome, chronic kidney disease)

Question 25

Rickets

Answer 25

increased melanin pigmentation and decreased exposure to sunlight + vegetarian diet (low in Ca, and vitamin D, high phytate and oxalate) + vitamin D deficiency (low 25-OHD is diagnostic) + inadequate calcium absorption to meet requirements =

Question 26

Consequences of vitamin D deficiency

Answer 26

multifactorial chronic disease -> osteoporosis and fracture, reduced muscle strength and increased falls, CVD, cancer (colon, breast and prostate), autoimmune diseases (osteoarthritis, diabetes, psoriasis, wheezing illnesses, lung function), tuberculosis, schizophrenia and depression

Question 27

Vitamin D

Answer 27

inhibits angiogenesis in growing tumors, getting some sunlight can be protective against melanoma!

Question 28

Sun exposure

Answer 28

Significant benefit in elderly people in regards to their vitamin D levels

Question 29

Subclinical deficiency

Answer 29

may contribute to poor bone health, other chronic diseases -> increased food fortification and increased supplements

Question 30

Bone health

Answer 30

reflects diet (especially fruits and veggies), lifestyle (moderate sun exposure and resistance exercise) and genes -> alkali sources, vitamin D sources and calcium all contribute