Oxygen and Dietary Antioxidants

Aeorobic organisms require oxygen, and have developed defenses against the reactive byproducts of oxidative metabolism. In aging and disease, these defenses may be overwhelmed; a diet rich in antioxidants may help maintain health.

Aeorbic Organisms Require Oxygen

Humans, and the majority of living things (the exception being some microorganisms), are aerobic organisms - they require oxygen to survive. Aerobic organisms use molecular oxygen as an essential player in the last step of the catabolism (break-down) of food molecules.

Despite the variety of foods that are part of a person’s diet, from pizza to sushi, all can be broken down into three main types of fuel: protein, carbohydrate (sugar), or fat. These fuels are metabolized into smaller and smaller parts, until finally the carbons in the fuels are released as carbon dioxide.

In the final steps of this process, electrons are collected and passed to molecular oxygen in the mitochondria, resulting in the formation of water.

This reaction (fuel plus oxygen yields carbon dioxide and water) is essentially the same reaction that describes the burning of paper or of hydrocarbon fuels. Biology has found a means to harness and control the “burning” of fuels.

Oxygen is Highly Reactive

However, there is a downside to relying on oxygen. Oxygen is highly reactive. Corrosion and rust are familiar examples of the reaction of the oxygen in the air with metal surfaces. Explosions are often the result of the violent oxidation reactions.

The final step of catabolism, taking electrons from food molecules and delivering them to oxygen to form water, occurs in the mitochondrion - a subcellular structure often called the powerhouse of the cell. Leak of electrons as they are transported in the mitochondria can result in the conversion of oxygen to the free radical superoxide.

Superoxide can damage nearby molecules like DNA. All cells including bacteria contain special enzymes, the superoxide dismutases, to remove superoxide by converting it into hydrogen peroxide. Other enzymes, including catalase and glutathione peroxidase, remove the hydrogen peroxide. If free metals are around, hydrogen peroxide will react to form hydroxyl radical, which is very highly reactive and quickly damages everything around it.

Under certain conditions, as in some diseases, the generation of these reactive oxygen species overwhelms the natural defenses and oxidative damage occurs.

A popular hypothesis in aging research is that oxidative damage contributes to aging. Certain types of oxidative damage do accumulate with age, though it is not clear whether this damage causes aging, or is simply associated with it.

Antioxidants

If oxidative damage contributes to aging and disease, can it be avoided?

Much work is ongoing to investigate the use of dietary or synthetic antioxidants to protect against disease, with some promising results in animal models. However, there is currently no convincing evidence of any protection against human disease provided by taking vitamin supplements.

A diet rich in fruits and vegetables remains the best approach to disease prevention. Such a diet provides known antioxidants, including vitamins E and C, and flavonoids. A healthy diet also likely provides additional protective components not yet identified. Dietary guidelnes have been published by the US Department of Agriculture.

Assorted fruit

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