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The dark side of oxigen
How free radicals cause damage and disease?
What are free radicals? Why are they damaging to the human body? And how do vitamin A, C, E and the other antioxidant nutrients help protect the body against free radical damage? We’ll attempt to answer these questions and help you understand why eating 5-8 servings per day of anti-oxidant rich fruits and vegetables can benefit your health. But first, a little background…
Background: A Brief Look at Chemical Bonding
To understand the way that free radicals and antioxidants interact, you must first understand a bit about cells and molecules. So here's a (very) brief refresher course in Physiology/Chemistry 101: The human body is composed of many different types of cells. Cells are composed of many different types of molecules. Molecules consist of one or more atoms of one or more elements joined by chemical bonds.
As you probably remember from your old high school days, atoms consist of a nucleus, neutrons, protons and electrons. The number of protons (positively charged particles) in the atom’s nucleus determines the number of electrons (negatively charged particles) surrounding the atom. Electrons are involved in chemical reactions and are the substance that bonds atoms together to form molecules. Electrons surround, or "orbit" an atom in one or more shells. The innermost shell is full when it has two electrons. When the first shell is full, electrons begin to fill the second shell. When the second shell has eight electrons, it is full, and so on.
The most important structural feature of an atom for determining its chemical behavior is the number of electrons in its outer shell. A substance that has a full outer shell tends not to enter in chemical reactions (an inert substance). Because atoms seek to reach a state of maximum stability, an atom will try to fill its outer shell by:
- Gaining or losing electrons to either fill or empty its outer shell
- Sharing its electrons by bonding together with other atoms in order to complete its outer shell
Atoms often complete their outer shells by sharing electrons with other atoms. By sharing electrons, the atoms are bound together and satisfy the conditions of maximum stability for the molecule.
How Free Radicals are Formed
Normally, bonds don’t split in a way that leaves a molecule with an odd, unpaired electron. But when weak bonds split, free radicals are formed. 1 Free radicals are very unstable and react quickly with other compounds, trying to capture the needed electron to gain stability. Generally, free radicals attack the nearest stable molecule, "stealing" its electron. When the "attacked" molecule loses its electron, it becomes a free radical itself, beginning a chain reaction. The chain reaction continues and can be "thousand of events long." 2. Once the process is started, it can cascade, finally resulting in the disruption of a living cell.
Any free radical involving oxygen can be referred to as reactive oxygen species (ROS). Oxygen centered free radicals contain two unpaired electrons in the outer shell. The electron transport chain (ETC), which is found in the inner mitochondrial membrane, utilizes oxygen to generate energy in the form of adenosine triphosphate (ATP). Oxygen acts as the terminal electron acceptor within the ETC. The literature suggests that anywhere from 2 to 5% 3 of the total oxygen intake during both rest and exercise have the ability to form the highly damaging superoxide radical via electron escape. During exercise oxygen consumption increases 10 to 20 fold to 35-70 ml/kg/min. In turn, electron escape from the ETC is further enhanced. Thus, when calculated, .6 to 3.5 ml/kg/min of the total oxygen intake during exercise have the ability to form free radicals4. Electrons appear to escape from the ETS at the ubiqunone-cytochrome c level.3
"Oxygen is essential for life itself. But did you know it is also inherently dangerous to our existence? I call this the "dark side" of oxygen. And as a result, we are essentially rusting both inside and out. The same process that causes a cut apple to turn brown or iron to rust is the cause of all the chronic degenerative diseases we fear and even the aging process itself.
Consider the aging of our skin. Oxidative stress is the cause of wrinkles, sagging skin, and age spots. The next time you are with a large gathering of people of different ages, observe closely the change you see in people’s skin. Aging is a process we all take for granted, but when you look more closely, and compare a baby’s face, to that of a grandparent’s, the effects of our largest organ being exposed to all the pollutants in the air, sunlight, and cigarette smoke is baffling. This aging of the skin is an outward manifestation of "oxidative stress," which is occurring within every cell in your body."5
Some free radicals arise normally during metabolism. Sometimes the body’s immune system’s cells purposefully create them to neutralize viruses and bacteria. However, environmental factors such as pollution, radiation, cigarette smoke and herbicides can also spawn free radicals.
Normally, the body can handle free radicals, but if antioxidants are unavailable, or if the free-radical production becomes excessive, damage can occur. Of particular importance is that free radical damage accumulates with age.
In a nutshell, this is how you could summarize his theory: The nucleus of an atom is surrounded by a cloud of electrons. These electrons surround the nucleus in pairs, but occasionally an atom loses an electron, leaving the atom with an "unpaired" electron. The atom is then called a "free radical", and it is very reactive. When cells in the body encounter a free radical, the reactive radical may cause destruction in the cell. According to Dr. Harmon's free radical theory of aging, cells continuously produce free radicals, and constant free radical damage eventually kills the cell. When free radicals kill or damage enough cells in an organism, the organism ages.6
Dr. Denham Harmon, M.D., Ph.D., first proposed a theory of aging as the indiscriminate chemical re-activity of free radicals possibly leading to random biological damage. His idea has had much experimental success, and it is now considered a major theory of aging. Dr. Harmon's theory implies that antioxidants such as vitamin C and vitamin E, which prevent free radicals from oxidizing (removing electrons from) sensitive biological molecules, will slow the aging process. Dr. Harmon launched his theory by showing, for the first time, that feeding a variety of antioxidants to mammals extended their life spans.
