Vitamin C improves exercise performance, but only in those that need it

Posted on Mon, 25 Apr 16

Antioxidant supplements are controversial because of mixed evidence for their benefit, but this may be because their benefits are limited to those that need them.  

“It has been suggested that part of the failure of antioxidant supplementation to reduce oxidative stress and promote health is that it has been administered in humans with normal levels of antioxidants,” point out the authors of a new study that set out to test the hypothesis that antioxidants would indeed work better for people with higher levels of oxidative stress. 

To test their theory they screened 100 men for vitamin C baseline values in blood then selected the 10 individuals with the lowest (LOW-C [35 ±  8 μ mol/L]) and the 10 with the highest vitamin C (HIGH-C [78 ±  11 μ mol/L]) values for their experiment.

Then they had the 20 subjects perform aerobic exercise to exhaustion, which increases oxidative stress, before and after vitamin C supplementation (1000mg 3 times daily) for 30 days.

Sure enough, they found that vitamin C benefited those with initially low blood levels, but not those whose levels were high to begin with.  Vitamin C supplementation improved physical performance (measured with VO2max) in the LOW-C group, which was also poorer to begin with. Additionally, vitamin C supplementation decreased oxidative stress (measured with F2-isoprostanes and protein carbonyls) to a greater extent in the LOW-C group and blunted elevations in oxidative stress more effectively.  

“A striking disagreement exists among studies regarding the influence of vitamin C supplementation on redox status and physical performance,” commented the authors. “Indeed, several studies have reported that vitamin C supplementation attenuates oxidative stress, others have reported that it induces a pro-oxidant effect and others have reported that it does not affect redox status. Likewise, several studies have indicated that vitamin C supplementation induces a positive effect, a negative effect, or no effect on exercise performance.”

There are many reasons for these discrepancies, they noted, but “we believe that probably the most important reason for this disagreement in the literature may be the indiscriminate use of participants. We suggest future studies to employ individuals with either decreased levels of antioxidants and/or increased levels of oxidant biomarkers.”

In other words, when considering antioxidant nutrients, we need to consider individual requirements, not indiscriminately assume everyone is the same or will respond the same way. 

Reference: 

Paschalis V, Theodorou AA, Kyparos A, et al. Low vitamin C values are linked with decreased physical performance and increased oxidative stress: reversal by vitamin C supplementation. Eur J Nutr. 2016 Feb;55(1):45-53.