Oxygen destabilizes molecules — for example, proteins, fats and DNA — making them react unpredictably and creating byproducts called reactive oxygen species (ROS). Sources of ROS can be exogenous (outside) or endogenous (inside).
Diseases such as cancer, cardiovascular disease and inflammatory conditions generate a continuous flow of endogenous ROS. This can become a downward spiral: ROS leave us more susceptible to disease, and the disease generates more ROS. Exogenous ROS come from food in the form of oxidized proteins and fats, pollutants, UV radiation, ozone, certain drugs and various pathogens.
|The lutein in egg yolks is more readily absorbed than lutein from plant sources.
Damaging oxygen compounds have different life-spans and attack different sites. Some last only a fraction of a second, doing damage quickly and locally. Others live longer and can migrate to harm distant sites. For an antioxidant to stop oxidation it's not enough to be powerful; it must be in the right place, at the right time.
Specific antioxidants may have characteristics that let them target a unique area. Because of the broad nature of oxidative threat, there's an equally broad network of defense, including certain enzymes, nutrients with antioxidant activity and phytochemicals.
Because of the vast nature of oxidative threat, there's an equally vast network of defense. This network includes specific enzymes, essential nutrients with antioxidant activity plus phytochemicals.
The Eyes Have It
One of the best examples of timely, site-specific defense is the protection from age-related macular degeneration (AMD) — the primary cause of blindness in seniors. The macula lutea is the portion of the retina responsible for clear, distinct vision.
According to Dr. Denise Deming of DSM Nutritional Products, Inc. (www.dsm.com), Parsippany, N.J., membranes of the retina are rich in essential fatty acids. Lutein and zeaxanthin are believed to protect these fatty acids from oxidation. They also act like polarized sunglasses, protecting the macula from light damage by filtering out harmful blue light.
Lutein and zeaxanthin are carotenoids, and like their cousins beta-carotene and lycopene, they act as antioxidants, blunting the attack of ROS. Research indicates higher consumption of dietary lutein and zeaxanthin may lower risk for AMD.
Lutein and zeaxanthin are also the only carotenoids found in the lens, though at lower concentrations than in the retina. It's known that populations with higher consumption of dietary lutein and zeaxanthin tend to have a lowered risk for both AMD and cataracts.
The old folk advice to eat carrots for your eyes is valid. Carrots are a great source of beta-carotene. The richest natural sources of lutein and zeaxanthin are egg yolks and dark green vegetables.
However, most American diets are deficient in fruits and vegetables in their diet, which may be why our risk of AMD and cataracts is many times that of other developed countries.
There is natural lutein in egg yolks, with amount depending on the chickens' diets. According to Craig Maltby of Kemin Foods (www.kemin.com), Des Moines, Iowa, lutein supplementation in chickens shows up in the yolk of the eggs. While the amount is much lower than in plant sources, it is more easily absorbed.
|Nuts (especially Brazil nuts), meats, grains and other plant foods are dietary sources of selenium.
Arguably the most basic internal ROS defense system consists of a team of enzymes such as glutathione peroxidase. Critical to the structure of the glutathione peroxidase member of this antioxidant team is the mineral selenium. Selenium, an essential dietary element, also contributes to immune function, growth and cell repair. Nuts (especially Brazil nuts), meats, grains and other plant foods are dietary sources of selenium.
The mineral can also be acquired in the inorganic form as a salt. However, the organic compounds, such as selenomethionine, are thought to be more effective than the inorganic forms.
There are potential interactions between various antioxidants. For example, selenium may work synergistically with vitamin A, vitamin E and beta-carotene in lowering the risk of cancer, while the protective effect of the inorganic sodium selenite against breast cancer in rat studies was cancelled out by supplementation with vitamin C. Yet vitamin C apparently does not diminish the protective effect of the organic selenomethionine.
Currently, the National Cancer Institute is conducting the Selenium and Vitamin E Cancer Prevention Trial (SELECT), a 12-year study focused on the role of selenium and vitamin E (separately and together) in the prevention of prostate cancer.
In the Balance
Health demands a balance between pro-oxidant and antioxidant forces that is specific to each site. Tipping the balance in favor of oxidation produces oxidative stress. Tipping the balance in the opposite direction results in reductive stress. Balance is highly complex. That's why simply dumping loads of non-specific antioxidants into a biological system doesn't necessarily spell fountain of youth.
By using focusing on individual antioxidants and their specific functions processors are in a good position to contribute to healthy diets and lifestyles that help protect the delicate oxidation/reduction balance on many different levels for many different systems.
|Good ROS, Bad ROS
Ironically, the damaging effect of ROS on cells is being taken advantage of in a radical new skin cancer therapy developed and tested at Ichilov Medical Center in Tel Aviv, Israel. The therapy uses a combination of amino acids and light to create oxygen radicals with photodynamics. In 85 percent of the cases tested the oxygen radicals destroyed the cancer cells.