成年男女性的維他命C建議每日定額補 (RDA) 給分別九十和七十毫克，而可承受上限(UL)為二千毫克。當人體吸收一日維他命C超越可承受上限，最常見的腸胃不適，例如，腹瀉和肚痛。



可能你會發覺RDA和UL之間有一大段差距，市面大多數維他命C補充劑中維他命C的劑量都是在這段差距之中。因此，有時根據指示服用這些維他命C補充劑應該不會引起太大問題。由於研究顯示人體中維他命C的吸收是可飽和的和取決於劑量的，這表示到某個份量的維他命C可令吸收飽和，而多餘的維他命C則會被排出身體，所以理論上，同一劑量的維他命C於一日分數次服用比起一日一次過服用更容易引起毒性。

不過，服用這些維他命C補充品，再加上正常飲食中的維他命C，可能會增加過量吸收的風險。一般來說，每食用份量的維他命C補充品含有大概一千毫克的維他命C。一些果酸多的生果會含更多的維他命C，例如，一個橙含有大約六十毫克維他命C，一個奇異果則含有大約一百二十毫克。多吃果酸多的生果加上服用維他命C補充品可能會導致過量的維他命C吸收，尤其是一些正在節食而只吃生果和蔬菜的人。

長期過量吸收維他命C可能會對一些有腎病和鐵新陳代謝失調的人分別增加患上腎石和鐵中毒的風險。

總括而言，正確的概念是，如果你缺乏維他命C的話，免疫系統一定會被減弱。而這個時間服用維他命C補充品便會十分有用。其他時間，有時根據指示服用維他命C補充劑可能會比恆常服用會來得安全，因為可以減低過量服用導致的副作用之風險。

The recommended daily allowances (RDAs) of vitamin C for adult man and woman are 90 and 75mg respectively while the tolerable upper intake (UL) is 2000mg, at which the most common side effect is gastronintestinal disorders, like osmotic diarrhea and abdominal pain.


You may notice that there is a wide range between RDAs and UL, where the pharmaceutical dose of vitamin C supplements usually lies. Occasional ingestion of them with suggested dose shall not cause a big problem to your body. Since research shows that vitamin C absorption is saturable and dose-dependent, which means the degree of vitamin C absorption will be saturated at a certain level and excess vitamin C will just be excreted, toxicity is theoretically more likely when several large doses of the vitamin are ingested throughout the day than when the same amount is ingested as one single dose.

However, it may increase the risk of over-dosage together with dietary sources. In general, each serving of vitamin C supplements contains around 1000mg vitamin C. Together with citrus fruits, for example, an orange contains around 60mg vitamin C, around 120mg in kiwi, excessive ingestion of vitamin C may be resulted, especially for someone on diet who eat only fruits and vegetables to keep fit.

Prolonged overdose of vitamin C may increase the risk of kidney stone and iron toxicity in those with renal disease and disorders of iron metabolism respectively.

In conclusion, the correct logic is that immune system must be compromised if you have vitamin C deficiency, during which corresponding supplements may be very useful for compensation. At other times, occasional vitamin C supplementation may be better than usual supplementation which may lead to higher risk of some side effects.



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