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effects on vitamin supplementation have been measured just using a gross measure in a . Maybe you can comment on that.

It seems to me that there are so many other potentially more sensitive measurements that we can make of metabolic responses to exercise that have been ignored for the most part because is easy to measure.

DR. CLARKSON: I agree. Many studies that we find have used but there are also several studies that used submaximal exercise and studies that used strength.

These are easy to measure. I think that is why they are used. Also, except for vitamin C where I only showed you three representative studies, mostly all the studies that are available were presented here. So it is not that there are a hundred other studies out there.

I think that more people should be involved in looking at the effects of vitamins on performance. I think one of the problems why people aren't involved in looking at vitamins is that it is hard to measure in the blood and therefore difficult to determine initial status.

PARTICIPANT: My question is specifically in terms of looking at measurements as opposed to plasma or sweat loss. What about some other measure—urine or something else.

DR. CLARKSON: Well, urine levels are hard to interpret because what happens is, as soon as you reach a threshold level the nutrient spills over, so you are not quite sure what urinary secretion means.

Does increased excretion mean you need less? Perhaps for a nonexercising person this is true. I am not ready to really believe that for an exercising person. In this case when you get an increased excretion it is not clear what this really means.

If I gave a sedentary individual large doses of a particular vitamin and it increases in the urine, then we would say, yes, the status is adequate and the person does not need a supplement.

However, when you add stressors like heat and exercise, I am not really sure what an increase in urinary levels of vitamins means.

PARTICIPANT: I just wanted to follow up one comment you had made on niacin. There are two papers—certainly submitted—in those studies Evelyn Stephasson(?) had administered niacin supplementation to individuals and had them exposed to heat and attempted exercise.

She found a very profound dilation and increased incidence of syncopy. So niacin supplementation in heat could actually reduce performance.

DR. CLARKSON: Yes, I mentioned the flushing.

PARTICIPANT: In the Strydom (Strydom et al., 1976) paper, do you hap-



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