Vitamin A is the name of a fat-soluble retinol-like substance that is stable to heat, acids and alkalis and is easily oxidised. There are two types of vitamin A. Vitamin A alcohol, which is found only in animal foods, is the original form of vitamin A. Carotenoids, which can be ingested from either plant or animal foods, are converted to retinol in the body at levels that vary from person to person. Vitamin A contains photoreceptors (i.e., retinoids) that help create the retina, which is important for night vision; promotes growth and development; and maintains normal skin and mucous membranes and a functioning immune system.
Related reading:Learn about vitamin A and its effects
維他命A常見運用方式
維他命A是人體所需的維他命之一,可通過膳食攝取。

維他命A健康功效
維他命A的重要生理功能包括:
1.有助於保持良好視力
維他命A可維持正常的視覺反應,有助於舒緩眼乾、保持健康夜間視力、年齡相關性黃斑老化等一些眼部退化問題。
2.促進生長發育
視黃醇可促進糖蛋白的生成,能促進發育,使骨骼更強壯,維持牙齒、牙床、皮膚、頭髮的健康。
3.有助於維持正常的免疫力
特別是呼吸道的身體抵抗力,有助於對維持呼吸道健康。
4.能維持上皮結構的完整和健全
預防皮膚黏膜乾燥角質化,外用有助於治療粉刺、膿包、膚表面潰瘍等。
維他命A缺乏時
若存在維他命A缺乏的情況,可能是維他命A攝入不足、脂肪吸收障礙或肝臟問題引起的。缺乏維他命A可導致發育不良,免疫功能及造血功能受損,更會影響眼睛健康,損害視力。

維他命A過量攝入
維他命A不宜過量攝取,單次大劑量攝取維他命A(超過200,000毫克)會導致視力模糊、惡心、嘔吐、眩暈;若長期每天服用超過10,000微克的口服維他命A將導致頭痛、惡心、皮膚過敏、腹瀉、關節和骨骼疼痛、出生缺陷、骨質變薄及肝損害。
維他命A與常見藥物
1.奧利司他可降低維他命A、其它脂溶性維他命及β-胡蘿蔔素的吸收,使血漿濃度降低。
2.類維他命A與維他命A同服,會使維他命A攝入過多,引起副作用。
3.抗凝劑與維他命A同服會增加出血風險。
4.貝沙羅汀與維他命A補充劑同服會增加副作用的幾率,如皮膚痕癢、乾燥。
維他命A食物來源
維他命A主要存在於動物肝臟、富含脂肪的魚類、蛋黃,及含胡蘿蔔素的蔬菜中。
Vitamin A-rich foods
- eggs
- 豬肝
- Broccoli
- cucurbit
- 哈密瓜
- 紅蘿蔔
- Kale
- 番茄

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