維生素 D 對健康的影響：缺乏標準、研究發現與補充建議

維生素 D 是一群脂溶性的荷爾蒙，對維持骨骼與肌肉健康至關重要，也與腎臟以外的組織、大腦功能、免疫、懷孕、癌症預防與心血管健康有關。除了從食物攝取，例如脂肪豐富的魚、魚肝油、蛋黃、波特菇、牛肝，以及早餐穀片、牛奶（含乳與非乳製品）、嬰兒配方奶、起司等強化食品，人體所需的維生素 D，有相當大一部分是靠皮膚接受陽光中的紫外線 B（UVB）合成。維生素 D 有兩種形式：維生素 D2（麥角鈣化醇）與 D3（膽鈣化醇）。

Vitamin D is a group of fat-soluble hormones that is vital for the maintenance of bone and muscle health. It is also vital for extra-renal tissues, brain function, immunity, pregnancy, cancer prevention, and cardiovascular health. In addition to food sources such as fatty fish, cod liver oil, egg yolks, portabella mushrooms, beef liver, and fortified foods such as breakfast cereal, milk (dairy and nondairy), infant formula and cheese, the human body uses ultraviolet B (UVB) radiation from sunlight to synthesize a significant portion of its vitamin D requirements. There are two forms of vitamin D: vitamin D2 (ergocalciferol) and D3 (cholecalciferol).

皮膚中的 7-脫氫膽固醇照射到陽光中的 UVB（波長 290–320 nm）後，會轉換成維生素 D3 前驅物（previtamin D3），再經由受熱的過程立即轉換成維生素 D。來自日曬與飲食的維生素 D2 與 D3 進入肝臟後，會轉換成 25-羥基維生素 D〔25(OH)D〕。25(OH)D 是血液中維生素 D 的主要形式，也是用來判斷維生素 D 狀態的指標。接著，25(OH)D 由維生素 D 結合蛋白（DBP）運送到腎臟，經 1α-羥化酶作用，形成具有荷爾蒙活性的 1,25-二羥基維生素 D〔1α,25(OH)2D〕。

Vitamin D3 is formed when 7-dehydrocholesterol in the skin is exposed to solar ultraviolet B (UVB, 290–320 nm) and converted to previtamin D3. In a heat-dependent process, previtamin D3 is immediately converted to vitamin D. Vitamin D2 and D3 resulting from exposure to sunlight and the diet are converted to 25-hydroxyvitamin D [25(OH)D] when they enter the liver. 25(OH)D is the major circulating form of vitamin D and is used to determine vitamin D status. Then, 25(OH)D is carried by DBP to the kidney, where hydroxylation by 1α-hydroxylase to 1,25-dihydroxyvitamin D [1α,25(OH)2D] occurs, producing the hormonally active form of vitamin D.

血清 25(OH)D 低於 20 ng/mL 屬於維生素 D 缺乏，低於 30 ng/mL（75 nmol/L）屬於不足；而 30–44 ng/mL 對肌肉骨骼、免疫、心血管健康與癌症等結果最有益。每天多補充 100 IU 的維生素 D，血清 25(OH)D 預期約上升 1 ng/mL（2.5 nmol/L）。25(OH)D 偏低，會增加多種慢性疾病、高血壓、糖尿病與癌症的風險。

Vitamin D deficiency is defined as a serum 25(OH)D level below 20 ng/mL and vitamin D insufficiency as less than 30 ng/mL (75 nmol/L), while a 25(OH)D level of 30–44 ng/mL provides optimal benefits for outcomes in musculoskeletal health, immunity, cardiovascular health and cancer. Serum 25(OH)D can be expected to rise by about 1 ng/mL (2.5 nmol/L) for every 100 IU of additional vitamin D each day. The consequences of low 25(OH)D status include increased risk of various chronic diseases, hypertension, diabetes and cancer.

美國國家醫學院（Institute of Medicine）建議，1 至 70 歲的多數人每天攝取 600 IU 維生素 D。

The majority of people between the ages of 1 and 70 should consume 600 IU of vitamin D daily, according to the Institute of Medicine.

70 歲以上、日曬很少的人，每天可能需要 800 IU。美國內分泌學會建議成人每天 1500–2000 IU、兒童 1000 IU。對於缺乏的人，維生素 D 應與鈣一起補充，以維持骨骼健康。

Those older than 70 years may need 800 IU per day, assuming minimal sun exposure. The Endocrine Society recommends 1500 to 2000 IU per day for adults and 1000 IU for children. Vitamin D should be given with calcium to maintain bone health in those who are deficient.

所有經檢測確認缺乏維生素 D 的成人，都應接受治療：每週 50,000 IU 維生素 D3，或每天 6000 IU，持續 8 週，使血清 25(OH)D 達到 30 ng/mL，之後再以維持劑量補充。美國內分泌學會的指引支持這項建議，並補充：1–18 歲可能需要每天 1000 IU、19–50 歲可能需要每天 1500–2000 IU 的維持劑量，才能讓血清 25(OH)D 穩定維持在 30 ng/mL 以上。

All adults found to be vitamin D deficient should be treated with either 50,000 IU of vitamin D3 per week or 6000 IU per day for 8 weeks to achieve a serum 25(OH)D level of 30 ng/mL. Treatment should be followed by a maintenance dose. The Endocrine Society's guidelines support this recommendation but add that a maintenance dose of 1000 IU per day may be needed to consistently raise serum 25(OH)D levels above 30 ng/mL in patients aged 1 to 18 years and as much as 1500 to 2000 IU per day in patients aged 19 to 50 years.

美國兒科醫學會建議，所有兒童從出生後數天起直到青春期，每天攝取 400 IU 維生素 D。

The American Academy of Pediatrics recommends that all children receive 400 IU per day of vitamin D from their first few days of life through adolescence.