Research shows that some medications can interfere with a workout. For example, beta-blockers slow the heart rate and make it hard to reach maximum heart rate goals. But prescription medications aren’t the only pills that Americans swallow on a daily basis. A survey by CRNUSA.org showed that 68% of American take one or more supplements and the survey revealed that 66% of younger supplement users will increase their supplement use over the next 5 years. That’s a hefty percentage! The reason most people take vitamins, minerals, and supplements components is because they believe they offer overall health and wellness benefits. A smaller percentage take supplements for specific purposes, like for joint or bone health.
Some supplements MAY offer health benefits, but the benefits for most aren’t proven. Even ones that show benefits early on sometimes turn out not to have clear benefits in later studies. For example, we’ve long associated calcium supplements with bone health, but more recent research shows calcium supplements don’t prevent bone fractures and may be harmful in other ways. For example, excess calcium may build up in the wall of the artery and, potentially, increase the risk of cardiovascular disease, based on some studies.
Still, people feel like supplements provide some protection against disease and take them despite a lack of strong evidence of benefits. We tend to focus on the upsides of taking supplements, but what about downsides? Supplement use is common among people who live a healthy lifestyle and among people who work out. Is it possible that supplements, like medications, can interfere with the benefits of exercise or with exercise performance?
Supplements and Exercise: Can They Interfere with Fitness Gains?
When you work out, your body adapts to the stress you place on it. These adaptations, depending upon the type of exercise, cause muscle growth, strength gains, or an increase in endurance. Interestingly, supplements that may be beneficial under the right circumstances could actually interfere with adaptations to exercise. An example is antioxidant supplements. These include vitamins A, C, and E. It’s not uncommon for people to take vitamin C in hopes of preventing a cold or take a multi-vitamin that contains all of the antioxidant vitamins. However, these vitamins in higher doses may make it harder for positive adaptations to take place.
In fact, a study published in The Journal of Physiology found that supplemental vitamin C and E blunted the positive adaptations to endurance exercise. One of the ways that endurance exercise gives you more stamina is by causing an increase in the number of mitochondria inside muscle cells, a process called biogenesis. When cells have more mitochondria, they can produce more ATP, the cell’s energy currency, with aerobic exercise. This helps sustain aerobic exercise longer.
Vitamins A, C, and E help counter oxidative stress by acting as antioxidants. That’s beneficial in some situations, yet it appears that oxidative stress is a signal for new mitochondria to form. If antioxidant vitamins vanquish free radicals and oxidative stress formed during exercise, the making of new mitochondria may be hampered, as several studies now suggest. It also appears, based on some studies, that vitamins A, C, and E block certain proteins that muscles need to develop greater endurance. One of these is called COX4.
It’s not clear what dose of antioxidant vitamins you’d have to take to interfere with exercise gains, and it’s not just antioxidant vitamins that are a problem. Another popular supplement called resveratrol may do the same thing. At one time, people took this supplement in hopes of preventing cardiovascular disease due to its antioxidant effects and studies suggesting it might slow aging. However, a small study published in The Journal of Physiology found that resveratrol actually interferes with some of the positive health benefits of exercise on the heart. For example, the participants didn’t see the same improvements in blood lipids in response to exercise when they took a resveratrol supplement.
What about Hypertrophy Training?
It appears that antioxidant supplements may diminish some of the benefits you get from endurance exercise, but does the same apply to resistance training? Again, skip the antioxidant supplements. A study published in the Journal of Physiology showed that the repair and remodeling of muscle after a resistance workout or high-intensity interval training is at least partially dependent on reactive oxygen species. These reactive oxygen species act as a signal for repair and growth to take place. Under conditions where there are high levels of antioxidants in the body, it might blunt muscle repair and growth by disrupting signaling pathways. At the very least, antioxidant supplements don’t help muscles to grow and, at worst, they interfere with training adaptations. According to the Cochrane Library, an esteemed resource for evidence-based medicine, antioxidant supplements also don’t reduce delayed-onset muscle soreness.
Still, There are Unanswered Questions
The question is how much supplemental antioxidants do you have to consume to interfere with training adaptations? If you take them in the morning and exercise in the evening, will they still interfere? Until we know more, it’s best not to take antioxidants within a few hours before or after a workout. Even better, get your antioxidants from whole food sources rather than supplements. Antioxidant vitamins in supplements are disconnected from the food they originated from and lack the other goodness that whole plants offer. Plus, independent testing shows that supplements often fall short in terms of how much of an active ingredient they contain and whether they have the active ingredient at all. Plus, some contain additives and contaminants that aren’t listed on the label. Supplements aren’t regulated like medications are, so you don’t always know what you’re getting. Be smart and get your “supplements” from nature’s pharmacy.
CRNUSA.org. “The Dietary Supplement Consumer”
Cochrane Library. “Antioxidants for preventing and reducing muscle soreness after exercise”
Paulsen, G., et al. 2014. “Vitamin C and E Supplementation Hampers Cellular Adaptation to Endurance Training in Humans: A Double-Blind Randomized Controlled Trial.” The Journal of Physiology, February, jphysiol.2013.267419.
The Journal of Physiology 591 (Pt 20): 5047–59. doi:10.1113/jphysiol.2013.258061.
The Journal of Physiology 594(18) · December 2015.