Bendich: There is an indication that there is some degree of "conditioning" in white blood cell levels of vitamin C, but this effect is temporary and blood levels of vitamin C do not indicate that vitamin C deficiency develops.

Passwater: Does vitamin C increase iron overload disease incidence?

Bendich: The overall scientific data do not support the premise that vitamin C causes iron overload in normal persons. However, persons with the genetic disorders of hemochromatosis or thalassemia major may find that vitamin C increases the iron toxicity that they are suffering from by mobilizing more of their stored iron. Persons with genetic iron disorders should consult their physicians about the use of vitamin C supplements.

The effect of vitamin C on iron absorption is still an area of active interest. Vitamin C appears to enhance the absorption of non-heme iron consumed in the same meal. However, this effect does not appear to continue to increase with increasing intake of vitamin C. Dr. Marvin Cohen and I reviewed 24 studies which included 1,412 subjects eating meals designed to measure the iron absorption at different levels of vitamin C. We found that vitamin C doses above the RDI level do not increase susceptibility to iron overload in normal individuals.

Passwater Is vitamin C an in vivo pro-oxidant or mutagenic?

Bendich: Harvard researchers have found evidence that vitamin C acts only as an antioxidant in vivo. [20] Even in the presence of transition metal ions, the researchers found that vitamin C acted as an antioxidant rather than a pro-oxidant.

Stich and others have shown that old suggestions that vitamin C might be mutagenic was due to a problem with the testing method. [21] Vitamin C has not been shown to be mutagenic. In fact, many published studies show that vitamin C has anti-mutagenic properties because it is an important antioxidant.

Passwater: Does vitamin C impair copper utilization?

Bendich: This has not been shown in controlled studies. Two groups have investigated this question without finding such a relationship. [22-23]

Passwater: When we were chatting at a scientific meeting a few years ago, you were trying to trace the report that vitamin E could raise blood pressure in some individuals. I remember that the Drs. Shute used to say that this could happen in some diabetics or those who had rheumatic fever. Were you ever able to find evidence to verify these reports? Does vitamin E increase blood pressure in some individuals?

Bendich: No. There are no published reports of increases in blood pressure in any of the placebo-controlled, double-blind studies with dosages up to 2,000 IU per day.

Passwater: Does vitamin E cause tiredness?

Bendich: There are no peer-reviewed, placebo-controlled studies to support this. There have been several studies to examine the safety of vitamin E even at very large doses, and none have reported this as an observation. Usually, the anecdotal reports often suggest increased energy levels.

Passwater: In 1974, I conducted a study of vitamin E usage and health effects [24]. Drs. Linus Pauling and James Enstrom used data from the California subjects in my study and they conducted a follow-up study that showed health benefits in taking supplements. [25] The data on vitamin E showed benefit at all intakes of vitamin E as shown in Table 1. Although, the data showed greater freedom from disease and longevity at the 300 to 499 IU per day levels than the levels above 1,000 IU per day, there was better longevity at all intakes of vitamin E than among those not taking vitamin E.