The University of Florida researchers said the study drew inappropriate and clinically irrelevant conclusions, had a small sample size, ignored positive outcomes and did not control for potentially confounding drug use.
“These issues are critical for proper interpretation of laboratory-based studies with small sample sizes, particularly given that even minor lifestyle changes could influence many of the selected outcomes,” wrote professors Thomas W. Buford and Stephen D. Anton from the University of Florida’s Department of Aging & Geriatric Research.
Their comments appeared in the Journal of Physiology, the same journal that published the initial study last year and a rebuttal last November by researcher James Smoliga, PhD, from High Point University in North Carolina, and Otis Blanchard, the president and chief technology officer of Texan player, Wilmore Labs.
Buford and Anton continued: “Additionally, there was no mention of potential dose issues. Given that the optimal dose of resveratrol for humans, and for ‘at risk’ populations in particular, is not currently known, this is an important consideration.”
“These issues certainly do not discount the importance of the study, but we would argue that they are cause for more cautious interpretation of the study's findings.”
“Surprising” omissions and questions of objectivity
Their harshest criticism was saved for what they called “surprising omissions” in the study that had a dosage of 250mg of resveratrol per day.
“Perhaps the most surprising aspect of the presentation of findings by Gliemann et al. was the lack of reference to the fact that resveratrol improved performance on the step test to a significantly greater degree than placebo,” they wrote.
“This is a surprising omission, given that this test was described as a ‘test of maximum functional capacity’. Notably, this result can only be found within a supplementary table (Table S2 of Gliemann et al.).”
“…We can only speculate on the rationale behind the decision not to report this important finding in the main document, but this omission raises some questions regarding the objectivity of the data interpretation.”
“As a result of the points raised above, we believe that the strongly worded statements that resveratrol ‘blunted’ or ‘abolished’ the beneficial effects of exercise are likely to be inappropriate.”
“Such conclusions could potentially discourage future investigations in this area.”
Responding to Smoliga and Blanchard in another letter in the journal last year, Gliemann and the other researchers defended their work: "It is true that resveratrol supplementation did not abolish all of the training induced positive effects on cardiovascular parameters but we found it remarkable how many of the adaptations were absent or blunted in the resveratrol group."
Aside from its cardiovascular links, resveratrol has been shown to have other benefits including for the skin and immune system.
Journal of Physiology
Volume 592, Issue 3, February 2014 pp 551–552
‘Resveratrol as a supplement to exercise training: friend or foe?’
Authors: Thomas W. Buford, Stephen D. Anton