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Everyone knows vitamins are vital. Norwegian researchers, however, believe taking too much vitamins C and E may interfere with the training effects of endurance exercise, at least on a cellular level.

A new study in the Journal of Physiology suggests that taking vitamin C and vitamin E supplements reduces the benefits of endurance training, by interfering adaptations to exercise by the energy-making mitochondria of muscle cells.

Led by Dr. Dr Gøran Paulsen of the Norwegian School of Sport Sciences, researchers recruited 54 healthy, young men and women to receive either a placebo pill (containing no active ingredients) or a supplement providing a daily dose of 1000 mg of vitamin C and 175 IU (235 mg) of vitamin E. All of the participants, whether they received a placebo or not, did 11 weeks of fitness training. Every week the participants did 4 to 6 sessions of sprints, 4 to 6 minutes of exercise at 90% of maximum heart rate. They also did four to six sessions of 30 to 60 minutes each at 70 to 90% of maximum heart rate.

Neither the study participants nor the researchers knew who received the placebo and who received the vitamin pill. The researchers did a muscle biopsy of each participant before and after the trial to measure the effects of training on the numbers and functioning of the mitochondria.

At the end of the 11-week trial, the researchers did not find that either group had achieved significantly different respiratory capacity. Both the vitamin-takers and the placebo-takers had close to the same O2 capacity. However, when the researchers compared the mitochondria in the muscles of the two groups, they found that the placebo group's muscle had more mitochondrial enzyme activity, while the vitamin group's muscle actually, on average, lost mitochondrial activity.

Both groups had roughly equivalent gains in actual performance. Only the their mitochondrial activity was significantly different. 

This was not the first time that scientists had discovered that antioxidant supplements seem to interfere with changes in the mitochondria of muscle cells. In 2011, a group of Australian scientists conducting a study with lab rats found that giving them vitamin E and alpha-lipoic acid reduced mitochondrial activity whether they were exercised or they were allowed to remain sedentary in their cages.

But 12 other studies have found that vitamin C and vitamin E in lower doses either have no effect or can actually improve mitochondrial function. In a study of 16 athletes, 8 of whom received a supplement containing approximately 28500 IU (17.1 mg) of beta-carotene, 319 mg of vitamin C, instead of 1000 mg of vitamin C, and 72 IU (48 mcg) of vitamin E, instead of 175 IU, all of them used for 3 weeks instead of 11 weeks, the energy-making capacity of muscle actually improved. Giving athletes a supplement containing just 6 mg (10000 IU) of beta-carotene, 200 mg of vitamin C, and 48 IU (36 mcg) of vitamin E for just 3 weeks also improved muscle energy capacity. On the other hand, a study giving both athletes and non-athletes 2000 mg of vitamin C every day for 28 days found no improvement, and a study giving 20 athletes and 20 non-athletes 1000 mg of vitamin C plus 660 IU of vitamin E every day during a 28-day training program also found that energy making capacity of muscle declined.

The message seems to be that a small dose of antioxidants may be helpful, while a large dose of antioxidants may be harmful--or at least not do any good.

Continue reading after recommendations

  • Paulsen G, Cumming KT, Holden G, Hallén J, Rønnestad BR, Sveen O, Skaug A, Paur I, Bastani NE, Ostgaard HN, Buer C, Midttun M, Freuchen F, Wiig H, Ulseth ET, Garthe I, Blomhoff R, Benestad HB, Raastad T. Vitamin C and E supplementation hampers cellular adaptation to endurance training in humans: a double-blind randomized controlled trial. J Physiol. 2014 Feb 3.
  • Strobel NA1, Peake JM, Matsumoto A, Marsh SA, Coombes JS, Wadley GD. Antioxidant supplementation reduces skeletal muscle mitochondrial biogenesis. Med Sci Sports Exerc. 2011 Jun,43(6):1017-24. doi: 10.1249/MSS.0b013e318203afa3.
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