Free radicals are linked to aging and a host of diseases, but little is known about their role in human health, or how to prevent them from making people sick.
What are free radicals?
Free radicals are thought to be responsible for age-related changes in appearance, such as wrinkles and gray hair.
Understanding free radicals requires a basic knowledge of chemistry.
Atoms are surrounded by electrons that orbit the atom in layers called shells. Each shell needs to be filled by a set number of electrons. When a shell is full; electrons begin filling the next shell.
If an atom has an outer shell that is not full, it may bond with another atom, using the electrons to complete its outer shell. These types of atoms are known as free radicals.
Atoms with a full outer shell are stable, but free radicals are unstable and in an effort to make up the number of electrons in their outer shell, they react quickly with other substances.
When oxygen molecules split into single atoms that have unpaired electrons, they become unstable free radicals that seek other atoms or molecules to bond to. If this continues to happen, it begins a process called oxidative stress.
Oxidative stress can damage the body's cells, leading to a range of diseases and causes symptoms of aging, such as wrinkles.
How do free radicals damage the body?
Free radicals are unstable atoms. To become more stable, they take electrons from other atoms. This may cause diseases or signs of aging.
According to the free radical theory of aging, first outlined in 1956, free radicals break cells down over time.
As the body ages, it loses its ability to fight the effects of free radicals. The result is more free radicals, more oxidative stress, and more damage to cells, which leads to degenerative processes, as well as "normal" aging.
Various studies and theories have connected oxidative stress due to free radicals to:
- central nervous system diseases, such as Alzheimer's and other dementias
- cardiovascular disease due to clogged arteries
- autoimmune and inflammatory disorders, such as rheumatoid arthritis and cancer
- cataracts and age-related vision decline
- age-related changes in appearance, such as loss of skin elasticity, wrinkles, graying hair, hair loss, and changes in hair texture
- genetic degenerative diseases, such as Huntington's disease or Parkinson's
The free radical theory of aging is relatively new, but numerous studies support it. Studies on rats, for example, showed significant increases in free radicals as the rats aged. These changes matched up with age-related declines in health.
Over time, researchers have tweaked the free radical theory of aging to focus on the mitochondria. Mitochondria are tiny organelles in cells that process nutrients to power the cell.
Research on rats suggests that free radicals produced in the mitochondria damage the substances that the cell needs to work properly. This damage causes mutations that produce more free radicals, thus accelerating the process of damage to the cell.
This theory helps explain aging, since aging accelerates over time. The gradual, but increasingly rapid buildup of free radicals offers one explanation for why even healthy bodies age and deteriorate over time.
Free radical theories of aging and disease may help explain why some people age more slowly than others.
Although free radicals are produced naturally in the body, lifestyle factors can accelerate their production. Those include:
- exposure to toxic chemicals, such as pesticides and air pollution
- fried foods
These lifestyle factors have been linked to diseases such as cancer and cardiovascular disease. So, oxidative stress might be a reason why exposure to these substances causes disease.
Antioxidants and free radicals
Antioxidants can help to prevent the harmful effects of free radicals. Antioxidants can be found in berries, citrus fruits, soy products, and carrots.
It is hard to watch television without seeing at least one commercial that promises to fight aging with antioxidants. Antioxidants are molecules that prevent the oxidation of other molecules.
Antioxidants are chemicals that lessen or prevent the effects of free radicals. They donate an electron to free radicals, thereby reducing their reactivity. What makes antioxidants unique is that they can donate an electron without becoming reactive free radicals themselves.
No single antioxidant can combat the effects of every free radical. Just as free radicals have different effects in different areas of the body, every antioxidant behaves differently due to its chemical properties.
In certain contexts, however, some antioxidants may become pro-oxidants, which grab electrons from other molecules, creating chemical instability that can cause oxidative stress.
Antioxidant foods and supplements: Do they work?
Thousands of chemicals can act as antioxidants. Vitamins C, and E, glutathione, beta-carotene, and plant estrogens called phytoestrogens are among the many antioxidants that may cancel out the effects of free radicals.
Many foods are rich in antioxidants. Berries, citrus fruits, and many other fruits are rich in vitamin C, while carrots are known for their high beta-carotene content. The soy found in soybeans and some meat substitutes is high in phytoestrogens.
The ready availability of antioxidants in food has inspired some health experts to advise antioxidant-rich diets. The antioxidant theory of aging also led many companies to push sales of antioxidant supplements.
Research on antioxidants is mixed. Most research shows few or no benefits. A 2010 study that looked at antioxidant supplementation for the prevention of prostate cancer found no benefits. A 2012 study found that antioxidants did not lower the risk of lung cancer. In fact, for people already at a heightened risk of cancer, such as smokers, antioxidants slightly elevated the risk of cancer.
Some research has even found that supplementation with antioxidants is harmful, particularly if people take more than the recommended daily allowance (RDA). A 2013 analysis found that high doses of beta-carotene or vitamin E significantly increased the risk of dying.
A few studies have found benefits associated with antioxidant use, but the results have been modest. A 2007 study, for instance, found that long-term use of beta-carotene could modestly reduce the risk of age-related problems with thinking.
What we do not know
Studies suggest that antioxidants cannot "cure" the effects of free radicals - at least not when antioxidants come from artificial sources. This raises questions about what free radicals are, and why they form.
It is possible that free radicals are an early sign of cells already fighting disease, or that free radical formation is inevitable with age. Without more data, it is impossible to understand the problem of free radicals fully.
People interested in fighting free radical-related aging should avoid common sources of free radicals, such as pollution and fried food. They should also eat a healthful, balanced diet without worrying about supplementing with antioxidants.