Story last updated at 4/4/2012 - 11:34 am
Oxygen is essential for life as we know it. However, it's a reactive and potentially toxic molecule as well.
Oxygen participates in nearly every organic reaction within our bodies, including deriving energy from food, and it is one of the most common chemical elements in biomolecules such as DNA and protein.
On the flip side, oxygen can damage DNA, proteins and fats. This damage can lead to mutations and is suspected to be a major contributor to multiple diseases and the overall ageing process. Antioxidants help us combat this oxygen paradox, and have garnered a lot of attention in popular medical and nutritional literature.
Here, the basics of oxidation biology will be discussed using the popular supplement and antioxidant, vitamin C as an example. First, a few basic definitions of terminology are presented below. Please note that oxidation biology is a complex and exciting topic; here we will barely skim the surface.
Oxidation: A chemical reaction that combines oxygen with another molecule accompanied by an exchange of electrons. More generally, oxidation is the loss of electrons from a substance, for example vitamin C, which are then gained by another molecule such as oxygen.
Reactive oxygen species: Oxygen can exist in many forms, including those which are very electron-hungry and particularly reactive. These reactive oxygen species include peroxides, such as hydrogen peroxide, and free radicals.
Anti-oxidant: A molecule, such as vitamin C, which can donate electrons to reactive oxygen species and neutralize them before they damage and react with other molecules such as DNA. In general, antioxidants work in concert with enzymes that can recycle them for reuse, enabling multiple cycles of oxidation.
THE MANY FUNCTIONS OF OXYGEN
Oxygen can wear many hats. The oxygen we breathe is molecular oxygen, present as the element O2. However, it can also be transformed through accepting electrons (e-) and protons (H+) to form the toxic molecule hydrogen peroxide (H202), which can then accept another set of electrons and protons to form water (H2O), as shown in the right panel of the accompanying figure.
Hydrogen peroxide is powerful enough to kill bacteria, which is why it's applied to wounds. The familiar fizzing when hydrogen peroxide is applied to a wound is due to the attempt of bacteria - and our cells - to neutralize the peroxide by converting it to O2 and H20 before it causes overwhelming damage leading to cell death.
However, the natural process of deriving energy from food, termed oxidative metabolism, also produces hydrogen peroxide. Excessive exercise, calories or exposure to environmental toxins increases oxidative stress leading to a higher likelihood for oxidative damage.
An inorganic example illustrates the oxidation process as well. Consider metal on a car that begins to rust. This is due to the elemental iron (Fe) in the metal reacting with oxygen in the atmosphere (O2) to form iron oxide (Fe2O3), which has the characteristic flaky reddish property of rust. By bonding with iron, oxygen is sharing electrons with iron but is not sharing fairly due to oxygen's desire to obtain more electrons.
Metaphorically speaking, unchecked oxidation in the body leads to rusty cells and biomolecules, therefore sophisticated inherent mechanisms disarm reactive oxygen species and our dietary choices can also supplement this process.
The term anti-oxidant refers to the ability of a molecule to donate electrons, and there are hundreds of molecules with this capability. Here, we discuss vitamin C because it is a relatively simple and common anti-oxidant.
Vitamin C can neutralize reactive oxygen species by providing them with electrons through the reaction illustrated in the left panel of the accompanying figure. Vitamin C can rearrange its bonding pattern to form oxidized vitamin C and release two electrons and two protons. These electrons and protons can bond with molecular oxygen and hydrogen peroxide, eventually producing water.
Mammals are certainly not the only organisms that utilize vitamin C as a protectant. For example, the process of photosynthesis in plants produces reactive oxygen species, which can cause significant damage to the chloroplasts that house the photosynthetic machinery. Therefore, plants synthesize a high level of vitamin C to minimize oxidation.
Humans cannot make vitamin C, so it must be obtained through diet. Certainly there is value in taking supplements. However, purified vitamins and antioxidant supplements are reportedly not as effective as eating foods naturally rich in antioxidants. The body has an easier time absorbing vitamins immersed in food than in more concentrated forms.
Also, the beneficial compounds present in foods are highly complex. For example, blueberries contain more than 20 classes of antioxidants; it would be a challenge to find such a comprehensive supplement. Local foods in Southeast Alaska are rich sources of antioxidants, which are present in basically all berries native to the region. Another reason to forage: The fresher the food, the higher the antioxidant activity. Focusing on vitamin C, some top local sources include wild rose hips, young fireweed leaves and low bush cranberry.
Jasmina Allen holds degrees in chemistry and biology and currently lives in Juneau.