Exercise, Free Radicals and Antioxidants

As most people know, exercise has many proven benefits. It can lower the risk of heart disease and positively impact blood pressure, cholesterol levels, bone mass and well being while aiding in weight control, to name a few. And yet exercise has a dark side. The very act that improves so many health parameters can also damage the body, increasing the exerciser’s risk of many maladies such as cancer and CAD. What, exercise damaging?! Yes. The dark side of exercise comes about through the increased production of free radicals.

What is a Free Radical?

A free radical is a molecule with one or more unpaired electrons in its outer shell (orbital). In the body this creates an unstable molecule that is highly reactive, setting off a chain reaction of damaging events as it searches for electrons to fill its outer shell. Numerous studies in recent years strongly implicate these free radicals in the development of a variety of diseases such as certain cancers, cardiovascular disease, autoimmune disorders and the aging process as a whole.

How Are Free Radicals Produced?

Free radicals are produced in the body in a variety of ways. A big contributor, especially for exercisers, is the production of oxygen free radicals through the electron transport chain (ETC), the body’s principle means of energy generation. Studies conducted in the ’70s and ’80s established a relationship with exercise, increased oxygen consumption and increased free radical production through the ETC.

Free radicals are a normal by-product of cellular energetics and the reduction of molecular oxygen. Exercise increases the rate at which these events occur, hence an increase in free radical production. During exercise, total oxygen consumption may increase 10-15 fold, and as much as 100 fold in active muscle, leading to significantly greater free radical production.

But this is just the tip of the iceberg. Other possible avenues of free radical production in exercisers include temporary tissue hypoxia (lack of oxygen) during heavy resistance training or high intensity anaerobic activity, reperfusion (return of blood flow and oxygen to muscle) following intense exercise, tissue trauma and inflammation, substrate depletion and hyperthermia (possibly promoting mitachondrial uncoupling). Add to these environmental factors such as ultraviolet radiation, alcohol, smoke and pollution, and a rather grim scenario unfolds.

Now That I’m Terrified, What Do I Do?

Fortunately, the body has enzyme systems in place whose purpose is to intercept these free radicals, convert them to less harmful substances and remove them from the body. These compounds are referred to as the antioxidants. Consider them the Justice League of the body, righting wrongs and stamping out evildoers.

Exercise has been shown to increase antioxidant activity and production, but only to a point. Frequent, exhaustive, long duration exercise, along with the above environmental factors, is simply too much for the body to handle on its own.

So, what is one to do? Ensure that an abundance of the nutrients involved in antioxidant activity are consumed. Eating a diet rich in fresh fruits and vegetables can certainly help and is recommended for everyone, intense exerciser or not. These foods contain many well-known and not so well known substances shown to aid in antioxidant activity and reduce the risk of disease and illness. The problem is that few people are willing or able to accomplish this.

What now? Well, if you cannot or will not get it from the diet; supplement. Food consumption surveys and countless studies show that Americans are not getting adequate, let alone optimal, nutrition from the diet. Knowing that the needs of exercisers are greater than those of sedentary individuals, the prospect of obtaining ideal nutrient intake from food alone is like the legend of Bigfoot: You’ve heard about it, but never actually seen it. The most important nutrients involved with antioxidant activity are Vitamins E and C, beta-carotene and the minerals zinc and selenium. These nutrients are either directly involved in neutralizing free radicals or are co-factors in enzyme systems that have antioxidant activity.

Benefits of Antioxidant Supplementation

The greatest body of research exists for vitamins C and E, individually and in combination. Additionally, minerals such a selenium and zinc have shown benefits. Following are some of the benefits to exercisers that antioxidant supplementation provides:

• Vitamin C
  • May aid recovery and reduce soreness and damage associated with unaccustomed exercise¹
  • Reduce cortisol, adrenaline and anti-inflammatory peptides (markers of muscle damage) in ultra-marathon runners^2,3
  • Fewer reported upper respiratory tract infections in runners⁴
  • Reduced LDL oxidation (CAD risk factor) and generation of LDL species from exercise⁵
• Vitamin E
  • Protects red blood cells from oxidative stress during intense exercise⁶
  • Protects against free radical induced muscle damage^7,8,9
  • Reduces damage from intense, eccentric exercise ¹⁰
• Combined Vitamin C, E and beta-carotene
  • Protect against and reduce physical and oxidative stress¹¹
  • May promote a more favorable testosterone/cortisol ratio¹¹
  • Enhanced antioxidant enzyme activity (superoxide dismutase and catalase) in neutrophils¹²
• Selenium
  • Selenium is a co-factor for the antioxidant glutathione peroxidase (GPX). Exercise increases activity of this enzyme, necessitating an increased intake ¹³
  • As part of GPX, combats oxidative stress¹⁴
• Zinc
  • Co-factor for the antioxidant enzyme superoxide dismutase (SOD)
  • Exercise increases losses and intake is typically low in athletes
  • Blocks the exercise-induced increase in reactive oxygen species (free radicals) ¹⁵

How Much Do I Need?

Safe and optimal intake of the listed antioxidants is listed in Table 1. Based upon current data and known upper limits and lowest observed adverse effect levels (LOAEL), these are the targets that a person should strive for.

REFERENCES

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