Reports that vitamins C and E may blunt the positive effects of exercise are misleading, according to an antioxidant expert.
German researchers have reported that antioxidant vitamins C and E may blunt the positive effects of exercise, with respect to insulin sensitivity. Findings were published in the Proceedings of the National Academy of Sciences.
Reacting to the study , Alexander Schauss, PhD, from AIBMR Life Sciences, a nutraceutical products consultancy, told NutraIngredients.com that the title of the study (Antioxidants prevent health-promoting effects of physical exercise in humans) was misleading.
“The primary objective of this study was to study the effect of a 4-week intensive 5-days a week exercise program on insulin sensitivity. Yet the title of the paper leads one to believe otherwise,” he said.
“This is a small gender-biased study of 40 male subjects, 25 to 35 years of age. When I read through the study for the first time I had to wonder how could the authors have come up with such a title for their paper?” he asked.
In addition to questioning the study design, particularly with respect to assigned both trained and untrained people to an intensive exercise programme of underwent 85 minutes of exercise five days per week for four weeks, Dr Schauss also questioned the conclusions drawn from the data.
“Skeletal muscle biopsies were obtained from the right vastus lateralis muscle of study subjects. But some of the data is missing for a number of subjects, and reported as such by the authors,” said Dr Schauss.
The authors noted that biopsies for the ‘early’ time-point were only obtained from five people in the vitamin group, and four in the placebo group. “Yet the authors conclude a “strong induction of PGCl-alpha, PGCl-beta, and PPAR-gamma expression in skeletal muscle following 4 weeks of exercise training in previously untrained, antioxidant naïve individuals” and “markedly reduced exercise-related induction” in those taking antioxidants, based on these limited number of biopsies,” said Dr Schauss.
“Would it not have made more sense to appropriately increase the intensity and duration of exercise slowly and then see if the subject’s bodies didn’t accommodate handling of ROS without a significant change in induction of these markers?” he said.
The study reflects a ‘transient’ increase in ROS during ‘limited periods of physical exercise only’, noted Dr Schauss, “whereas the bulk of the literature, including that in non-primate models have not observed these concerns obtained in models of ‘continuous exposure to increased levels of ROS’”, he said.
Dr Schauss also noted that the authors presented no evidence of adverse effects by any of the individuals from vitamin C and E supplementation.
British Nutrition Foundation comment
Adding to the debate, Dr Elizabeth Weichselbaum, nutrition scientist from the British Nutrition Foundation, said: “This study shows that just because something is good for you, it does not mean that more of it is better! Vitamins C and E are antioxidants naturally occurring in many foods, mainly fruits and vegetables (vitamin C), and vegetable oils (vitamin E).
NOW the delimma surfaces: First, if you take too many antioxidants, they might stop benefical free radicals from switching on glucose/ insulin uptake. Then, blood sugar levesls increase which damage tissues. High amounts of antioxdiants are protective against this damage. The following research shows that low levels of antioxidants are often associated in diabetes.:
From: Duke University Medical Center
Antioxidants May Reduce Harmful Complications Of Diabetes
SAN FRANCISCO -- Duke University Medical Center researchers have found that the depletion of body chemicals called antioxidants may increase the risk of complications from the most common form of diabetes.
The scientists recommend that diabetics take antioxidant supplements, such as vitamin C or E, to help stave off or even forestall the hallmark complications of diabetes, including blindness, kidney failure, amputation and even death.
Antioxidants neutralize oxygen "free radicals," highly reactive chemicals that are the potentially destructive byproducts of the body's process of turning food into energy. Normally, the body produces enough antioxidants of its own to keep the reactive oxygen from causing damage.
"We were able to show that patients with poor control of their diabetes who were beginning to show signs of complications had depleted their store of antioxidants," said Duke researcher Dr. Emmanuel Opara in an interview. "Further, we found a significant correlation between high blood-sugar levels and depletion of antioxidants.
"It appears that this depletion is a major risk factor for developing complications, and that antioxidant supplements could lower this risk," he concluded.
Opara prepared the results of his studies for presentation Sunday (April 19) at Experimental Biology `98, the annual scientific meeting of the Federation of American Societies for Experimental Biology (FASEB).
The researchers studied 50 similar people with Type II diabetes -- also known as non-insulin-dependent or adult-onset diabetes. In this form of the disease, insulin produced in the body is unable to trigger the lowering of high blood sugar. Type II diabetes afflicts about 90 percent of the estimated 10.7 million Americans diagnosed with the disease and the 5.4 million believed to have undiagnosed cases, according to the Centers for Disease Control and Prevention.
Insulin is the hormone that normally regulates the level of sugar (glucose) in the blood and is produced by cells in the pancreas. Insulin is secreted when the level of blood glucose rises -- as after a meal.
All diabetic patients in the study were taking only drugs referred to as sulfonylureas, which increase the sensitivity of receptors to insulin throughout the body. Half the patients exhibited microalbuminuria, the excretion of tiny amounts of protein in the urine that is considered a precursor of kidney disease, while the other half did not.
The researchers took blood samples from all 50 patients, as well as a control group of 20 similar people without diabetes, and determined levels of antioxidants in their blood.
"We found that the non-diabetics' ability to defend against damage from the oxygen free radicals was almost twice that of those patients exhibiting microalbuminuria," Opara explained. "And while the difference between the two diabetic groups was not as pronounced, the difference was still statistically significant. Also, antioxidant depletion correlated with high blood sugar after meals only in the group with microalbuminuria."
The researchers determined antioxidant levels by a new chemical assay developed at King's College in England that enabled them to measure all known antioxidants in the blood and to obtain a more global picture of the body's total antioxidant capacity, Opara said. Other assays are only specific for individual antioxidants.
Using the newly developed assay, the scientists rated the ability of the non-diabetics to defend against free radical damage at 2.7, compared with 1.4 for those with microalbuminuria and 1.7 for the diabetics without microalbuminuria.
Though the exact mechanism of action of the oxygen free radicals is not yet clear, these findings confirm in humans earlier animal studies of the chemicals' role in damage in diabetes, Opara said. Previous Duke studies by Opara have shown that vitamin E can delay the development of diabetes in obese rats with Type II diabetes, and that the depletion of the antioxidant glutathione caused diabetes in another rat model.
"The results we've been seeing in our animal studies are now being borne out in humans,' Opara said. "I recommend that since the body has many antioxidants, diabetics should take a number of these agents, including vitamins C and E, and N-acetylcysteine."
The diabetic patients involved in the current study come from Eygpt, and their samples were brought to Duke by E. Abdel-Rahman, one of Opara's collaborators.
Joining Opara in the study, which was partly funded by the Duke department of surgery, were, from Duke, Dr. Somaya Soloma, Dr. James Lowe, and Dr. Salah Abdel-Aleem.