22. "Bone cross-section" by Pbroks13 - Own work. Licensed under CC BY 3.0 via Wikimedia
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The body regulates calcium homeostasis with two pathways;
one is signaled to turn on when blood calcium levels drop below normal and one is the pathway that is signaled to turn on when blood calcium levels are elevated.
Vitamin D metabolic pathways have been most extensively studied in areas related to its anti-rachitic effects and mineral ion homoeostasis, including the hormonal control loop involving serum calcium levels, parathyroid hormone, induction of 1-α hydroxylase, synthesis of 1, 25-OH D2, and the resulting alterations in intestinal and renal handling of mineral ions, as well as its effects on osteoblasts. Classically, clinical effects of vitamin D deficiency are considered to be the result of reduced intestinal absorption of calcium that in turn raises parathyroid hormone levels, and is accompanied by accelerated bone de-mineralization to maintain serum calcium concentration. Following chronic, severe vitamin D deficiency, frank hypocalcaemia ensues, but patients rarely present with acute symptoms (e.g. tingling or tetany), as this usually develops over an extended period of time. Rather, the most common presenting symptoms of vitamin D deficiency include vague, local, or diffuse musculoskeletal aches and pains.
Remodeling : Approximately 10% of the skeletal mass of an adult is remodelled each year
The purpose of remodeling is to regulate calcium homeostasis, repair microdamaged bones from everyday stress, and also to shape and sculpt the skeleton during growth.
Calcium supplementation alone has shown little benefit in treating or preventing osteoporosis. But, combined with vitamin D, calcium supplementation can slow the rate of bone loss by as much as thirty percent and it offers significant protection against hip fractures. The recommended dosage for calcium is 1,000 mg daily.
Vitamin D is found in eggs, butter, fatty fish, liver, and fortified foods such as milk, orange juice, and cereal.自然界中含維他命D的食物極少
vitamin D decreases with age
容易發生維他命D缺乏症的人包括：餵母乳的嬰兒，50歲以上的老人，不常接觸日晒的人，皮膚顏色比較暗的人種，以及肥胖的人
Vegan sources
Lichen
Cladina arbuscula specimens grown under different natural conditions: The contents of vitamin D3 range from 0.67 to 2.04 μg g⁻¹ dry matter in the thalli ofC. arbuscula specimens grown under different natural conditions.[165]
Animal sources[160]
Fish liver oils, such as cod liver oil, 4.5 g (1 teaspoon) provides 450 IU (100 IU/g)
Fatty fish species, such as:
Salmon, cooked, 85 g (3 oz) provides 444 IU (5.2 IU/g)
Mackerel, cooked, 85 g, 390 IU (4.6 IU/g)
Tuna, canned in oil, 100 g, 269 IU (2.7 IU/g)
Sardines, canned in oil, drained, 100 g (3.5 oz), 193 IU (1.9 IU/g)
Cooked egg yolk provides 44 IU if egg weighs 61 g (0.7 IU/g)
Beef liver, cooked, 85 g, provides 42 IU (0.5 IU/g)
Mechanism of epithelial Ca2+ transport.
Epithelia can absorb Ca2+ by paracellular and transcellular transport. Passive and paracellular Ca2+transport takes place across the tight junctions and is driven by the electrochemical gradient for Ca2+ (blue arrow). The active form of vitamin D (1,25-(OH)2D3) stimulates the individual steps of transcellular Ca2+ transport by increasing the expression levels of the luminal Ca2+ channels, calbindins, and the extrusion systems. Active and transcellular Ca2+ transport is carried out as a three-step process. After entry of Ca2+ through the (hetero)tetrameric epithelial Ca2+ channels, TRPV5 and TRPV6, Ca2+ bound to calbindin diffuses to the basolateral membrane. At the basolateral membrane, Ca2+ is extruded via an ATP-dependent Ca2+-ATPase (PMCA1b) and a Na+/Ca2+exchanger (NCX1). In this way, there is net Ca2+ absorption from the luminal space to the extracellular compartment.
Vitamin D is photosynthesized in the skin and is also acquired by dietary intake.
Two hydroxylation steps in the liver and the kidney are required for vitamin D activation, forming 1, 25-dihydroxyvitamin D. UVB, ultraviolet radiation in B-wavelength region (320–290 nm).
Vitamin C can support calcium absorption,
High levels of calcium in the body can also contribute to low stomach acids, so taking extra vitamin C can support the digestion process.
magnesium is essential for absorption and metabolism of calcium.
Magnesium also has a role to play, together with the thyroid and parathyroid glands, in supporting bone health:
stimulating the thyroid’s production of calcitonin, which acts as a bone-preserving hormone, and regulating parathyroid hormone, a function of which is to regulate bone breakdown in a number of ways.
Mg is fundamental for ATP, the main source of energy in the cells.
A high-protein diet is associated with increased excretion of calcium in the urine and increased risk for osteoporosis, too.每天需求量約為0.8公克/每公斤體重
Raising daily protein intake from 47 to 142 grams doubles the excretion of calcium in the urine. However,
too little protein is also associated with an increased risk for osteoporosis
In contrast, a vegetarian diet is associated with a lower risk of osteoporosis
A diet high in salt or acid ash also causes calcium removal from bones and increases calcium loss in the urine.
Therefore, we recommend avoiding salt and eating an alkaline based diet. Basically, an alkaline diet is one that focuses on vegetables, fruit, nuts, and legumes while avoiding overconsumption of meat and dairy.
Soft drinks containing phosphates (phosphoric acid) are definitely linked to osteoporosis because they lead to lower calcium levels and higher phosphate levels in the blood. When phosphate levels are high and calcium levels are low, calcium is pulled out of the bones. The phosphate content of soft drinks, such as Coca-Cola and Pepsi, is very high, and they contain virtually no calcium.
foods containing refined sugar generally do not contain calcium.
Carbon monoxide, is one of the main toxic ingredients in cigarettes that results in the lower blood oxygen level in the smoker. It readily binds to the hemoglobin in the blood making it difficult for oxygen to be taken up and distributed to the rest of the body.
This can lower the body oxygen content in a heavy smoker by as much as 15%.
As a result of all these harmful smoking effects on the body, there is less overall nutrition being delivered to the skeletal tissue so there are fewer raw materials delivered to the new bone cells.
high alcohol consumption has profound effects on the ability of the liver to metabolize certain chemicals, among them hormones, which are themselves fundamental for bone health.
Chronic, excessive alcohol use carries another hidden danger for people already prone to osteoporosis, in the form of nerve damage to the lower extremities.
This so called alcoholic peripheral neuropathy causes numbness in the feet and legs with consequent loss of balance, leading to frequent falls, thus greatly enhancing the chances for fractures.
