We all know exercise is beneficial to our health. Then why is it that ultramarathon runners may generate so many free radicals during a race that they can damage the DNA of a significant percentage of their cells? Researchers have looked at the exercise-induced increase in free radical production as a paradox: why would an apparently healthy act--exercise--lead to detrimental effects through damage to various molecules and tissues? This arises out of somewhat of a misunderstanding: exercise in and of itself is not necessarily the healthy act--it's the recovery after exercise that is so healthy, the whole "that-which-doesn't-kill-us-makes-us-stronger" notion. For example, exercise training has been shown to enhance antioxidant defenses by increasing the activities of our antioxidant enzymes. So, during the race ultra-marathoners may be taking hits to their DNA, but a week later they can experience great benefits, as shown in my video, Enhanced Athletic Recovery Without Undermining Adaptation.
In a recent study, researchers from Oregon State University looked at the level of DNA damage in athletes. Six days after a race, athletes didn't just go back to the baseline level of DNA damage, but had significantly less, presumably because they had revved up their antioxidant defenses. So, maybe exercise-induced oxidative damage is beneficial, similar to vaccination. By freaking out the body a little, we might induce a response that's favorable in the long run.
This concept, that low levels of a damaging entity can up-regulate protective mechanisms, is known as hormesis. For example, herbicides kill plants, but in tiny doses may actually boost plant growth, presumably by stressing the plant into rallying its resources to successfully fight back.
Wait a second, though. Could eating anti-inflammatory and anti-oxidant rich plant foods undermine this adaptation response? We know that berries may reduce inflammatory muscle damage (See Reducing Muscle Soreness with Berries), and greens may reduce free radical DNA damage (See Preventing Exercise Induced Oxidative Stress with Watercress). Dark chocolate and tomato juice appear to have similar effects. How it works is that flavonoid phytonutrients in fruits, vegetables, and beans seem to inhibit the activity of xanthine oxidase, considered the main contributor of free radicals during exercise. And the carbs in plant foods may also decrease stress hormone levels.
So in 1999, a theoretical concern was raised. Maybe all that free radical stress from exercise is a good thing, and increased consumption of some antioxidant nutrients might interfere with these necessary adaptive processes. If we decrease free radical tissue damage, maybe we won't get that increase in activity of those antioxidant enzymes.
A group of researchers who performed a study on tart cherry juice and recovery following a marathon responded to this antioxidant concern by suggesting that, although it is likely that muscle damage, inflammation, and oxidative stress are important factors in the adaptation process, minimizing these factors may improve recovery so we can train more and perform better. So, there are theories on both sides, but what happens when we actually put it to the test?
While antioxidant or anti-inflammatory supplements may prevent these adaptive events, researchers found that blackcurrant extract - although packed with antioxidant and anti-inflammatory properties - actually boosted the health benefits of regular exercise.
If we take antioxidant pills--vitamin C and vitamin E supplements-- we can also reduce the stress levels induced by exercise, but in doing so we block that boost in antioxidant enzyme activity caused by exercise. Now maybe we don't need that boost if we don't have as much damage, but vitamin C supplements seem to impair physical performance in the first place. With plant foods, though, we appear to get the best of both worlds.
For example, lemon verbena, an antioxidant-rich herbal tea, protects against oxidative damage and decreases the signs of muscular damage and inflammation, without blocking the cellular adaptation to exercise. In a recent study, researchers showed that lemon verbena does not affect the increase of the antioxidant enzyme response promoted by exercise. On the contrary: antioxidant enzyme activity was even higher in the lemon verbena group. In my video, Enhanced Athletic Recovery Without Undermining Adaptation, you can see the level of antioxidant enzyme activity before and after 21 days of intense running exercises in the control group. With all that free radical damage, the body started cranking up its antioxidant defenses. But give a dark green leafy tea, and not only do we put a kabosh on the damage due to all the phytonutrients and antioxidants, but we still get the boost in defenses--in fact, in this case, the boost was even greater.
Find out more on enhancing athletic recovery in this three-part video series:
-Michael Greger, M.D.
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