Antioxidant Nutrients Fight the Bad Boys of Disease
All the vitamins play unique roles in the body, but one special ability of some vitamins is taking the spotlight-antioxidant activity. It's this activity that scientists think is the protection against a host of diseases including heart disease, cancer, and Alzheimer's disease because compounds called free radicals may be at the root of these. The next sections provide a simplified overview of how researchers think antioxidant nutrients fight disease. Three nutrients, the carotenoids, vitamin E, and vitamin C, make up the antioxidants. To understand antioxidants and how they fight disease, we need to look at the most basic level in the body, the cell.
The cell membrane is composed primarily of proteins and lipids. These lipids are polyunsaturated, a chemical term that distinguishes them from either saturated or monounsaturated fats (similar to the different forms of dietary fat that we eat). Saturation refers to hydrogen atoms, but you probably recognize these different fats as either artery friendly or the kind that raise your blood cholesterol. The polyunsaturated lipids are more susceptible to oxidation, or combining with oxygen, which generates free radicals. Free radicals are unstable compounds that keep damaging other compounds in a cascade reaction that doesn't stop until an antioxidant comes along.
By attacking the polyunsaturated fats in the cell membrane, the free radical damages the membrane so it can't do its job of protecting the cell. Free radicals also damage other structures inside the cell, including DNA and other molecules such as LDL, cholesterol carriers in the blood. Scientists think that free radicals initiate cancer by causing this damage to the cell and also instigate many of the events leading up to a heart attack.
The production of free radicals occurs during normal metabolism, from exposure to certain dietary components, cigarette smoke, sunlight, smog, or other substances in the environment. Over a lifetime, free radicals may even be responsible for some of the degenerative aspects of aging. Antioxidants grab the free radicals and prevent the damage from spreading to other cells and compounds.
Antioxidants Fight Heart Disease
Exciting research on antioxidants has helped scientists work out theories about how these nutrients protect against heart disease. Most agree that atherosclerosis is most likely the underlying cause of most heart attacks, many strokes, and other diseases of the heart and blood vessels. This process takes place slowly over the years and probably begins in childhood. The linings of the arteries become coated with deposits consisting of cholesterol, fats, and other compounds (called plaques). This used to be called "hardening of the arteries" because it caused the vessels to become rigid and less elastic.
The deposits cause a narrowing and scarring of the arteries, impeding blood flow. Eventually the deposits can grow together, and the artery can close off completely, or a blood clot may form and plug up the narrowed artery. If the blood was on its way to the heart, the result is a heart attack. If the blood was on its way to the brain, a stroke occurs. The blood carries oxygen to these organs, and when the blood can't reach them, this lack of oxygen causes damage and tissue death.
Lipoproteins, which scientists classify by their density, serve as taXicabs in the bloodstream for cholesterol and fats (which aren't soluble in water, and therefore not in blood): VLDL, LDL, and HDL. They're made up of two parts, one which is attracted to water, and another which is attracted to fat. This means that they can pick up fat soluble compounds such as cholesterol with the fat-loving end and travel in a water-based substance such as blood.
Your total blood cholesterol level, which should be 200 or less, is made up of all these lipoproteins. LDL carries cholesterol from the liver where it's made and carries it into the blood, making it more likely that the cholesterol will be deposited in the artery. In contrast, HDL picks up cholesterol in the blood and takes it back to the liver, where it's broken down and disposed of, so HDL is protective. A high level of cholesterol in the blood is considered one of the main risk factors for heart disease because it leads to atherosclerosis. It may be more important, however, to know the ratio of HDL cholesterol to LDL cholesterol rather than just total cholesterol.
This doesn't completely explain a heart attack or stroke. Although high blood cholesterol is a major risk factor, some people with normal levels will have heart attacks and strokes. Some researchers have suggested that the road to a heart attack may be a three-stage process similar to cancer: initiation, progression, and termination. During initiation, the tissue inside the artery suffers an injury. In the progression stage, plaques accumulate in the blood vessel. Finally, in termination, a blood clot forms in the vessel, leading to a heart attack.
Among known risk factors for CVD, some that have been thought to cause injury to the vessels include smoking, hypertension, and the aging process. Studies dating back to the early 1980s indicate that various types of lipid oxidation products, and also LDL cholesterol that has been modified by free radicals, may cause injury. Now researchers believe that these compounds may be involved in all three stages of CVD.
Antioxidants may playa role in CVD prevention by protecting the vulnerable compounds from becoming oxidized. Some of the studies in this area have focused on the essential nutrients with antioxidant functions, such as vitamins C and E and betacarotene. So far, evidence for vitamin E preventing heart disease is the strongest, mostly because of its function as an antioxidant.
The carotenoids vary as to their antioxidant abilities, and lycopene significantly outpaces both betacarotene and lutein. Although antioxidant activity seems to be the main reason for their potential role in CVD and cancer prevention, lab studies suggest that, in addition, carotenoids slow down cell proliferation and differentiation, an important step in cancer development. In addition, research results show other biologic activities of the carotenoids including an immunity-boosting effect.
How Cancer Develops
Over the past decades, accumulating environmental problems and more complex lifestyles in concert with an increased life expectancy have forced Americans to focus on cancer as a major health problem. Cancer is now the second leading cause of death in adults and children in the United States, preceded only by CVD in adults and accidents in children. Worldwide, the burden of cancer is equally mindboggling, with more than 7.6 million new cases every year. Scientists think that up to 80 percent of all cancers are caused by environmental factors and up to 40 percent of those by diet.
The term cancer covers a lot of ground and represents a large group of diseases that are highly diverse. But the common thread is the presence of unrestrained growth of cells that began life as normal cells. If you had to name a cause of cancer, it would be the loss of control over normal cell reproduction. Scientists believe that a normal cell transforms into a cancerous cell by going through three stages: initiation, promotion, and progression. In the initiation phase, the genes that control cell reproduction produce a mutation in the cell. Several agents in our environment may trigger the mutation, often by free radical damage: UV light, radiation, chemicals, and viruses. Since the rate of cancer increases with age, researchers also believe that the aging process in cells itself may be involved in cancer cell development.
Even though the tendency for a cell to transform into cancer is initiated, the cell can remain dormant for years. Then, something comes along, a promoter, that activates the dormant cell. This activation by a promoter is called the promotion phase. .Promoters change the expression of the genes, or the proteins they make, but scientists haven't figured out the exact nature of this step. The last phase, progression, consists of a sequence of steps. Progression is equally as mysterious, but it probably involves the development of cells into a more malignant state. The final result of the three-stage process are cells that divide in an uncontrolled manner and have the ability to invade nearby structures, eventually traveling far from the original cancer site. This spreading of the cancer from the site of origin is called metastasis.
While the three-stage process seems to put the pieces together, scientists are still uncertain about that very first step, a normal cell developing into cancer. Even that step probably has many complex stages. One thing scientists are fairly clear on is that some aspects of lifestyle are strongly linked to a higher rate of cancer, such as chewing tobacco, smoking, or exposure to chemical toxins. And in a way that is becoming more clear with every genetic study, having certain genes and eating certain foods may provide some protection. This belief is based on the fact that people who are exposed to the same carcinogens don't have the same risk for the disease. One of the most exciting theories involves naturally occurring oxidants and compounds in foods that appear to fight them.
Antioxidants Battle Cancer
Scientists are relatively certain of how free radicals cause cell damage that might lead to cancer, but most of that evidence comes from petri dishes in the lab or in vitro studies. Exactly how this might work in the more complex human animal still needs more study.
One of the prominent theories that implicates the oxidation process as the major evildoer is apoptosis, the process of programmed cell death. Scientists now think that free radicals from the environment and our own bodies, and more specifically their subsequent damage, are most likely involved in the first two stages of cancer development, initiation and promotion.
Enough studies over the past several decades have shown that a person's diet can influence the rate of cancer to lead the National Cancer Institute to place a 40 percent figure on that source. But tangled among the weeds of possible carcinogens in food are the latest darlings of the nutrition world, nutritive factors that probably act as anticarcinogens, so that foods serve as both a source of a variety of carcinogens and protective substances. The carcinogens include pesticides, both synthetic and naturally occurring in plants, toxins from microbes, and the result of processing and cooking.
Besides being outright carcinogens, other compounds in food, even some nutrients, may act as promoters in cancer development. A bundle of epidemiologic studies support a strong link between high-fat diets, alcohol, and cancer incidence, with high-fat diets and alcohol use promoting cancer, not actually causing it. In contrast, diets high in fiber, fruits, and vegetables are associated with a lower risk for cancer. As researchers first tried to figure out which nutrients in the protective foods (mostly fruits and vegetables) were the protective compounds, they looked to essential nutrients. The logical choices were vitamins E and C, and vitamin A as beta-carotene. But the more they studied these seemingly simple plant foods, the more complicated it became. An entire world of mysterious pig ments and other substances began to emerge, substances previously thought to be merely responsible for putting color on your plate.
As for the vitamins, most studies that consider people's intake have shown that higher intakes of vitamins C and E and carotenoids are linked to lower risk of several types of cancer. For example, a recent review of the studies to date showed that people eating a diet high in fruits and vegetables had a 40 percent lower risk for gastrointestinal and respiratory tract cancer. When scientists pulled out specific vitamins from the diet by computing the amount of each, vitamin C carne out on top in cancer protection for those types of cancers. When it came to the types of cancers that are influenced by hormones, such as prostate and breast cancer, carotenoids were most effective, and probably a special one, lycopene, had the edge in prostate cancer.
But to truly prove the connection, intervention studies in which subjects take a supplement of the nutrient would have to turn up positive results. And in this area, the results are mixed at best. So why do the epidemiologic studies show consistent results, but not the intervention studies? Experts have suggested a few possible explanations. It may be that the vitamins and other protective compounds work best together, but, when given without their teammates, they lose their advantage.
Another possibility is that cancer is too complex a disease, developing sometimes over a lifetime, that even the timing of a treatment with vitamins is impo$sible to hit just right. And maybe it's not just timing the intervention-the studies might not last quite long enough to achieve a protective effect against a disease that takes years to even get going. So for now, the only sure thing is a diet that's high in fruits, vegetables, and other foods linked to lower cancer risk. The American Cancer Society has gone on record with the following advice for different types of cancer.
Breast Cancer
This is a leading cancer site for American women, second only to lung cancer. The studies linking diet to this disease are sometimes hard to interpret because of many influencing factors that are difficult to control, such as circulating hormone levels throughout life, age of menses onset, number of pregnancies and age at first one, duration of breast-feeding, body weight, and exercise. A new area of study involves the phytoestrogen compounds found in soybeans and a few other foods. These compounds are similar to natural estrogen, which studies show is a problem at higher levels. They tend to take its place, but not exert weaker effects, which may protect against breast cancer.
Best Advice
Strictly limit alcohol or avoid it altogether; eat a diet high in fruits and vegetables; eat soy foods; be active; keep weight within a normal range.
Colon and Rectal Cancer
These cancers are the second leading cause of cancer death in both American men and women. They are highly treatable if caught early, but they are easy to miss, often with no symptoms until the cancer has spread.
Best Advice
Eat a diet high in plant foods (fruits, vegetables, whole grains); avoid too much red meat and other animal products; avoid highfat foods; eat plenty of low-fat dairy products; exercise and stay in a good weight range.
Endometrial Cancer
This cancer of the lining of the uterus is strongly linked to body weight. One factor may be high estrogen levels, so soy foods may be helpful.
Best Advice
Maintain a healthy weight by exercising; eat a healthy diet that includes soybeans.
Lung Cancer
Lung cancer is a major killer of Americans-the leading cause of cancer deaths. Most lung cancers are related to tobacco smoking, probably up to 80 percent, with even passive inhalation recently cited as causing this cancer.
Best Advice
Don't smoke, or if you do, quit; eat a diet high in fruits and vegetables (do the 5-a-Day thing, or more!).
Mouth and Throat Cancer
Smoking is the culprit here, too, but so is chewing amt.snuffing the stuff. And there is an additive effect when a person uses tobacco and drinks too much alcohol.
Best Advice
Avoid tobacco; go light on alcohol; eat a diet high in fruits and vegetables.
Prostate Cancer
When French president Francois Mitterand died of this disease, Americans became more aware of its lethal effects. Because it tends to be slow growing, it's another type of cancer that is easy to treat early, but easy to overlook, too. This cancer is influenced by male hormones, much the same as breast cancer and reproductive organ cancers in women. But dietary factors are becoming more important as new studies emerge.
Best Advice
Limit animal foods such as red meats and high-fat dairy products; limit total intake of fat; eat plenty of fruits and vegetables, and especially tomatoes and tomato products (high in lycopene).
Stomach Cancer
Good news on this front-the rate of this cancer is dropping around the world. One causative factor may be a bacteria, helicobacter pylori.
Gastritis and ulcers may also be caused by the bacteria, and both diseases increase the risk for stomach cancer. If you have had chronic gastritis or ulcers, you should get checked for the bacteria and, if you come up positive, insist on antibiotic treatment. Diet also shows up as an important factor in most studies.
Best Advice
Do the 5-a-Day!
Do you notice that mantra, 5-a-Day or Better? The fruit and vegetable connection seems to be the strongest for many types of cancer.
Color and crunch are the keys to those vitamins that fight disease. The best part is that the foods containing these vitamins also contain those mysterious nonnutrients, the phytochemicals that work alongside their more established peers to add punch in clobbering free radicals that cause disease.
The different colors tell you which vitamins and phytochemicals the food contains. Crunch tells you that you're getting plenty of those touchy vitamins destroyed by cooking, such as vitamin C, and crunch usually spells fiber. So pull out your food records again and a palette: Be prepared to be a vitamin artist!
The color groupings are mostly fruits and vegetables, with the exception of Dark Brown that covers high-fiber grains. The 5-a-Day recommendation suggests increasing fruit and veggie intake, but five servings is actually a minimum can help you determine your intake of these color groupings. The amount that's right for you depends on how many calories you should be eating, with a range of five to eleven servings that covers a calorie range of 1,200 to 3,000.