Vitamins can be classified into two main groups. Fat soluble vitamin are stored in adipose tissue in the body and as a result daily intakes are not required. However, water soluble vitamins are not generally stored in humans, and as a result a more consistent intake is required to maintain tissue levels. Vitamin C is a water soluble vitamin that is not stored to any great extent in humans. As a result it must be consumed frequently or tissue levels can fall and a vitamin deficiency or insufficiency can develop. Some studies have looked at vitamin C dosing in order to establish the amount of vitamin C required in humans. Generally the result of such studies have shown that plasma levels of vitamin C continue to rise with intakes of up to around 2500 mg per day, but after this extra vitamin C is not able to cause further rises. However, most of the benefits of high intakes of vitamin C are seen with doses of around 500 mg per day. After the 500 mg per day intake is reached the law of diminishing returns is seen with higher intakes up to the 2.5 gram threshold.
The question of how often vitamin C should be taken to maintain plasma levels has also been investigated by researchers. For example, in one study1, researchers compared two groups of individuals who were given the recommended 60 mg per day vitamin C. However, while one group received the vitamin C as a 240 mg dosing of vitamin C every 4 days the other group received their vitamin C in three 20 mg doses per day. So the vitamin C intakes were the same, but one group consumed their vitamin C far more frequently. The baseline readings for vitamin C were 1.26 mg per dL in all subjects, which indicated that their normal diets contained over 100 mg per day of the vitamin. The result showed that initially during the depletion days, the subjects consuming the single 240 mg dose experienced low levels of plasma vitamin C (0.74 mg per dL) compared to the subjects consuming the vitamin C more frequently (1.02 mg per dL). However, over time this difference disappeared such that the two groups maintained the same plasma levels of vitamin C.
These results suggest that the subjects adapted to the less frequent intake of vitamin C and that over time the 240 mg dose every 4 days provided similar plasma levels of vitamin C to the more frequent dosing. It is known that the body can adapt to low intakes of vitamins. Take a look at the typical Western diet, and you will see foods devoid of meaningful levels of micronutrients. However, even this diet prevents the development of the classical deficiency disease because the body can adapt to very low levels of vitamins and minerals by increasing absorption and decreasing excretion. In this experiments the subjects taking the vitamin C in a single 240 mg dose did attain higher peak plasma levels (during dosing days) compared to the 20 mg divided dose despite the mean plasma levels being similar. The authors also measured the white blood cell count of vitamin C, as this is an important determinant of the efficiency of the immune system. However, there were no differences between the two groups.
Dr Robert Barrington’s Nutritional Recommendation: In this study subject adapted to the low intakes of vitamin C on certain days. Some research suggests that taking high doses of vitamin C can also cause the body to adapt by retaining less vitamin C. Taking very high amounts of vitamin C and suddenly ceasing supplementation can therefore cause a precipitous drop in vitamin C levels for a period of time while readjustment occurs. It is therefore recommended that vitamin C intakes are tapered down when lowering doses to prevent this rebound vitamin C deficient state. Many people take vitamin C in supplements daily in doses of between 500 mg and 2500 mg. If this higher dose is taken in supplements it is therefore important that days are not missed as this potentially exposes the individual to low plasma levels of ascorbic acid.
RdB
