Lecture 19: Nutrition and the ageing bone Flashcards
Definition osteoporosis =
Progressive, systemic skeletal disease characterized by low bone mass and micro architectural deterioration of bone tissue, with consequent increase in bone fragility and susceptibility of fracture.
DEXA can pick up X. Some say density as well, some say not
low bone mass
What do osteoclasts and blasts do?
Osteoclast = responsible for resorbing bone (turquoise). They munch away at the surface, leaving a cavity.
Osteoblast = makes new bone matrix
Why need osteoblasts and clasts?
- Enables bone to adapt to mechanical loading, - repair damage
- regulate circulating Ca levels
- contribute to acid/base balance
Target drug strategies =
regulators of bone turnover
Serum calcium/blood values: good marker for calcium homeostasis?
No, The body will do anything to ensure this calcium levels will remain in a small range in the blood. There is no functional marker
Explain calcium homeostasis
When blood levels fall, there is an action on PTH:
- stimulates Ca uptake in kidneys -> active vit D increases Ca uptake in intestines
- stimulates ca release from bones
3 blood ca levels rise
The three calciotrophic hormones are:
- PTH
- 1-25-D (active vit D)
- Calcitonin (takes calcium from blood and puts it back in bone)
Conflicting data: dietary calcium associated, or not associated with risk of fracture.
what can you conclude?
More calcium is not necessarily better, but avoiding a low calcium intake is beneficial for the ageing skeleton.
How do you know whether the sun has the right UVB exposure to make vit D
Shadow shorter than your height? Right vit D level!
Why is the name vit D confusing?
Vitamin = vital amine, but vit D = pro-hormone. Main source is not diet, but UV exposure
Explain vit D uptake by the sun
UVB: absorbed by cholesterol in the skin -> previt D3 -> Vit D3 ->(liver) 25-hydroxyvitamin D3 (clacidiol) ->(kidney) Calcitriol (active vit D)
What is the marker for vit D status?
25-hydroxyvitamin D3
Can never reach vit D toxic levels via sun, true/false?
true
UK guidelines for vit D = 10 microgr/day = less than European committee and EFSA. UK = prevent deficiency, the rest = optimal health.
ok
Cycles of rising and falling vit D: bad for health?
If your change in vit D is very high, lost more bone and had increased bone resorption.
vit D3 vs D2?
bioavailability seems to be higher in D3. Elevates D3 levels.
Vit K: vital for bone health. Why?
Vit K is vital: it produces an AA called Gla which acts like glue to keep the calcium in bone.
Mechanistically, vit K is very important for bone. But in RCTs, vit K story is not showing a benefit.
How does bone help in maintaining the proper pH in the blood? What is the downside of this?
Bone is a huge reserve as alkaline salts. Using these salts to buffer the pH of the blood, might result in gradual decline in bone known as osteoporosis.
How does it work that bone buffering can lead to osteoporosis?
When reducing the pH medium in which bone cells operate, bone cells become hyperactive and you lose a lot of bone. As we get older, we become more acidic.
DASH study: increasing fruit & veg intake significantly decreased amount of calcium that is lost.
nois
