Carcinogens and mutagens

As mentioned above, mutagens are things that cause mutations to a cell's DNA, and a mutation is required for cancer to start. Needless to say, mutagens should be avoided as much as possible because if your cells don't mutate, you can't get cancer. There really are two categories of carcinogens: carcinogens and procarcinogens. Carcinogens directly cause mutations, while procarcinogens need an agent for them to be able to cause a mutation. For the sake of simplicity, we use the term carcinogen to refer to both categories throughout the book. Mutagens can be classified into three categories: physical, chemical and biological.

Physical mutagens

include ionizing radiation (typically from X-rays, radon gas and cosmic rays), ultraviolet radiation (typically from the sun's rays) and mineral fibers, namely asbestos. Ionizing radiation.

• X-rays are one of the strongest mutagens out there. The dose required to induce cancer is rather high, but it is also cumulative. This means that the more X-rays you get throughout your life, the more your cancer risk increases. It seems that repeated low levels of radiation are more dangerous than a single large dose. You should avoid any unnecessary X-rays.
• Cosmic rays, also known as gamma rays, are all around us and there is nothing we can do to avoid them. They are, however, stronger at higher altitudes, so if you live at a high altitude above sea level you should be aware that you have greater exposure.
• Radon gas results from the natural breakdown of uranium. It can creep into your home if you live near uranium mines. You can buy a radon detection kit at most hardware stores if you want to test your home. Should you find elevated levels of radon, you should contact your local Environmental Protection Agency (EPA) office.

Ultraviolet (UV) radiation

• UV light is the part of sunlight's spectrum that burns our skin. As we all know, exposure to the sun's rays is a major cause of skin cancer. Most of your skin cancer risk is determined by the amount of sunlight exposure you receive as a child and adolescent, and especially by the number and severity of sunburns you received. This does not mean that after you reach the age of eighteen you should start sun tanning as much as you want. You should really avoid the sun's rays as much as you can during your entire life, and if you must be in the sun you should definitely wear sunscreen with an SPF of 30 or greater. Children should always use a sunblock with an SPF of 30 or greater.

Asbestos

• Asbestos is found in some building materials such as insulation and roofing. These tiny fibers can become airborne very easily and get into your lungs. Once in your lungs, they can cause genetic mutations to your cells that often lead to lung cancer.

Chemical mutagens

are just what they sound like: chemicals that can cause genetic mutations. Most carcinogens are probably of this nature and they include, but are not limited to, the following:

• Benzopyrene – found in cigarette smoke and tar
• Iron – excessive iron consumption in people with high transferring saturation (iron stores) increases cancer risk significantly
• Nitrosamines – found in cigarette smoke and certain foods (see nitrites below also)
• Heavy metals such as lead, mercury and cadmium
• Nitrites – a food additive (found in cold-cuts and other cured meats among other things) that turns into carcinogenic nitrosamines in the stomach
• PCBs – found in some packaging materials
• Hormones given to cattle that we take in through their meat and milk
• Pesticides and insecticides such as DDT
• Aflatoxin – a chemical sometimes found in moldy corn and peanuts.

Biological mutagens

include viruses and bacteria. The best-known ones are the human papilloma virus (HPV), the Epstein-Barr virus, Hepatitis B and C viruses, and Helicobacter pylori (a bacteria).

• HPV often leads to cervical cancer.
• Hepatitis B and C viruses have been linked to liver cancer.
• Epstein-Barr virus can lead to certain lymphomas (cancers of white blood cells).
• Helicobacter pylori is associated with stomach cancer.

Free radicals

Free radicals (or oxidants) are highly reactive forms of oxygen or nitrogen that are produced by the body's metabolism, environmental factors, inflammation and sometimes by infection. Molecules are made up of atoms held together by chemical bonds. Each chemical bond consists of a pair of electrons. When a bond is broken, two molecular fragments (or atoms) are left over, each of which contains one unpaired electron. These atoms are highly charged and highly unstable because of the unpaired electron. These charged, highly unstable, and very reactive particles are known as free radicals.

Free radicals usually exist only for a small fraction of a second and spend their short lives racing around looking for molecules to combine or react with. These reactions are called oxidation, a process that is very similar to the formation of rust on metal. When a free radical combines with a molecule, it can damage the molecule and consequently the cell it belongs to. The damage can occur to cell membranes, proteins, lipids (fats), or to the cell's DNA. It is this damage to the cell's DNA that eventually leads to cancer. It is also believed that free radicals cause damage to cells that results in what we know as aging.

The body has about 1 trillion cells, and each cell is estimated to receive around 10,000 free radical hits each day. Part of the reason there are so many oxidative reactions is that each reaction causes a chain reaction. Thus, one free radical potentially leads to the creation of hundreds of thousands of others. The good news is that we have an antioxidant defense system that protects us from this barrage of cellular attacks. Antioxidants react with free radicals and end the chain reactions that could lead to cellular damage. If we did not have a good defense mechanism, our body would break down very quickly.

It is important to note that most of the mutagens mentioned in this section, such as ionizing radiation, heavy metals, cigarette smoke, alcohol, fat (see below for alcohol and fat), iron and other chemicals, generate free radicals. Free radicals are also produced as a result of exercise. However, regular exercise enhances the antioxidant defense system and therefore protects the body against damage that would otherwise be caused by these free radicals.

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