骨の生成もカルシウム、Vit.B、日光、Phoshate塩と肝臓などの臓器たちなど中々難しいものである。母乳にはVit.Dが極めて少ないのですね。
precisionnutrition.com/genetics-vitamin-d
photobiology.com/reviews/previtamin/
middlepath.com.au/qol/sunlight_vitamin-D_skin-cancer_suntan_sunburn.php
Vitamin D is manufactured in the skin following direct exposure to sunlight. The amount of vitamin D produced in the skin varies depending on time of day, season, latitude and skin pigmentation.
Usually 10-15 minutes exposure of hands, arms and face two to three times a week (depending on one's skin sensitivity) is enough to satisfy the body's vitamin D requirement.
Using sunscreen markedly diminishes the manufacture of vitamin D in the skin, as do window glass, clothing and air pollution. Skin color also affects vitamin D production; the fairer you are, the more you make and the quicker you make it.
There probably is a phototherapy effect that goes well beyond the biochemistry of vitamin D production. Even if you're just looking at vitamin D, there are so many healing benefits of vitamin D that it's worth promoting sunlight exposure for that reason alone. Vitamin D regulates the growth of cancer cells.
It impairs the proliferation of cancer tumours in the body, and at the same time it is extremely important for absorption of calcium in the small intestine.
Babies need vitamin D for healthy growth and development.
It helps them build strong, healthy bones and teeth.
Babies who don�t get enough vitamin D are at risk of getting rickets, a disease that affects the way bones grow and develop.
＜くる病＞ 乳幼児に増える 母乳、日光浴不足、食事が要因
毎日 5月2日(金)11時1分配信 news.yahoo.co.jp
栄養不足の時代に多かった乳幼児の「くる病」が最近、増えている。紫外線対策の普及や母乳栄養の推進などが複合的に関係しているという。専門医は
「くる病は母乳で育っている子どもに多く、特に注意してほしい」
と呼びかける。
くる病は、ビタミンＤが極端に不足することで血中のカルシウム濃度が下がり、骨の変形や成長障害などを引き起こす。歩き始める１歳以降、足に負荷がかかってＯ脚になりやすい。
東京大大学院の北中幸子准教授（小児医学）によると、１９９０年代はほとんどみられなかったが、２０００年ごろから学会報告が目立ち始め、最近は臨床現場で珍しくなくなった。
東大病院ではこの１０年ほどで、診断したり他施設からの相談を受けたりしたケースが約１００件に上る。
ビタミンＤが欠乏している乳幼児の増加の３大要因は、
▽母乳栄養の推進
▽日光浴不足
▽偏った食事
－－という。
母乳は赤ちゃんに大切な免疫物質が含まれるなど利点が多いものの、ビタミンＤは人工乳に比べて極めて少ない。
また、ビタミンＤは太陽の光にあたると体内で作られるが、皮膚がんやしみ・しわ予防の観点から紫外線対策が普及したことも影響している。
食物アレルギーでビタミンＤを多く含む卵や魚などを取るのを制限している場合もあり、こうした要因が重なると発症しやすい。
北中准教授は
「世界的にもビタミンＤ欠乏症が増えている。予防策として、特に母乳で育てている子には、日焼けしない程度に日光浴させたり離乳食で魚を取らせたりしてほしい」
と話す。
日本小児内分泌学会は昨年、診断の手引きを作成した。血中ビタミンＤ（２５ＯＨＤ）濃度の測定や膝関節のエックス線画像などで診断するが、２５ＯＨＤの測定は保険適用になっていないなどの課題もある。
【下桐実雅子】
Fig. 1. Schematic representation of the synthesis and metabolism of vitamin D for regulating calcium, phosphorus and bone metabolism.
publichealthreviews.eu/show/f/35
Note: During exposure to sunlight, 7-dehydrocholesterol in the skin is converted to previtamin D3. PreD3 immediately converts by a heat dependent process to vitamin D3.
photobiology.info/Photochem
Excessive exposure to sunlight degrades previtamin D3 and vitamin D3 into inactive photoproducts.
Vitamin D2 and vitamin D3 from dietary sources is incorporated into chylomicrons, transported by the lymphatic system into the venous circulation.
Vitamin D (D represents D2 or D3) made in the skin or ingested in the diet can be stored in and then released from fat cells.
Vitamin D in the circulation is bound to the vitamin D binding protein which transports it to the liver where vitamin D is converted by the vitamin D-25-hydroxylaseto 25-hydroxyvitamin D [25(OH)D].
nature.com/nrd/journal/v9/n12/fig_tab/nrd3318_F1
This is the major circulating form of vitamin D that is used by clinicians to measure vitamin D status (although most reference laboratories report the normal range to be 20-100 ng/ml, the preferred healthful range is 30-60 ng/ml).
It is biologically inactive and must be converted in the kidneys by the 25-hydroxyvitamin D-1α-hydroxylase (1-OHase) to its biologically active form 1,25-dihydroxyvitamin D [1,25(OH)2D].
Serum phosphorus, calcium fibroblast growth factors (FGF-23) and other factors can either increase (+) or decrease (-) the renal production of 1,25(OH)2D.
1,25(OH)2D feedback regulates its own synthesis and decreases the synthesis and secretion of parathyroid hormone (PTH) in the parathyroid glands. 1,25(OH)2D increases the expression of the 25-hydroxyvitamin D-24-hydroxylase (24-OHase) to catabolize 1,25(OH)2D to the water soluble biologically inactive calcitroic acid which is excreted in the bile.
1,25(OH)2D enhances intestinal calcium absorption in the small intestine by stimulating the expression of the epithelial calcium channel (ECaC) and the calbindin 9K (calcium binding protein; CaBP).
1,25(OH)2D is recognized by its receptor in osteoblasts causing an increase in the expression of receptor activator of NFκB ligand (RANKL).
Its receptor RANK on the preosteoclast binds RANKL which induces the preosteoclast to become a mature osteoclast. The mature osteoclast removes calcium and phosphorus from the bone to maintain blood calcium and phosphorus levels.
Adequate calcium and phosphorus levels promote the mineralization of the skeleton.