It's well known that the vitamins in food slow or prevent the onset of chronic disease. Fruits and vegetables, in particular, are rich sources of a variety of nutrients, including not only vitamins, but also trace minerals, and fiber, as well as many other classes of biologically important compounds, such as antioxidants and essential fatty acids.
The vitamins in food and the chemicals in plants stimulate the immune system, increase the activity of detoxification enzymes, reduce the formation of potentially life-threatening blood clots, lower blood pressure, and have antibacterial, antiviral, antifungal, and antioxidant effects.
The vitamins in food are one of the few questions in nutrition about which scientists agree. Their beneficial effects have been proven in animals and in humans, in the lab and in the study of whole countries, over the short term and over the long term, for treating disease and for preventing it. Let's look at just a few of the many ways the vitamins in food enhance health.
Many of the vitamins in food are potent antioxidants. Oxidative damage to the membranes lining cells and the DNA within them can occur when "burning" free radicals of oxygen are produced more rapidly than antioxidants can "quench" them. Free radicals are produced naturally as the cells use oxygen, and they are also produced in response to tobacco smoke, many drugs, environmental pollutants, solvents, radiation, and high-fat or high-sugar diets. If excess free radicals are not removed as quickly as they are produced, they can damage DNA. This sets up the cell for mutation and malfunction, or even cancer.
Antioxidant vitamins in food can stop this dangerous cycle, especially vitamins C and E and beta-carotene. Scientific tests find that consuming the equivalent of 800 IU of vitamin E daily can stop the production of harmful free radicals on red blood cells, reducing the risk of atherosclerosis. Consuming 20 mg of beta-carotene removes free radical indicators from the breath of smokers.
Similar effects are found for the flavonoids, non-vitamin antioxidants, found in abundance in vegetable juice extracts from carrots, parsley, beets, broccoli, kale, cabbage, spinach, and tomatoes and fruit juice extracts from apples, oranges, pineapples, papayas, cranberries, and peaches.
Another important function of the vitamins in food is detoxification. Many harmful chemicals our bodies absorb from the environment and from our diets don't actually become toxic until they are activated by the liver. The chemical means the liver uses to convert environmental chemicals into their toxic forms are varied and complex, but they can be stopped by numerous constituents in plant foods, including flavonoids, isothiocyanates, and ally sulfides, found in foods such as apples, grapes, grapefruit, onions, garlic, cabbage, Brussels sprouts, kale, and watercress. The same detoxification process lowers the potency of estrogen (reducing the symptoms of PMS or fibrocystic disease) or testosterone (helping the prostate).
The vitamins in food also stimulate the immune system. The nutrients in fruit and vegetables have positive effects on almost aspects of the immune system. Diets rich in fruits and vegetables increase resistance to infectious disease, especially in the elderly. This is especially true of vitamin C, beta-carotene, folic acid, vitamin B-6, and the form of vitamin E known as alpha-tocopherol. Taking these vitamins as supplements is just as effective for strengthening the immune system, and seems to have the added benefit of preventing allergies. The combination of vitamins C and E increases the body's production of the body's tumor fighter TNF-alpha, whether taken as vitamins in food or as supplements.
Fruits and vegetables can also lower cholesterol and blood pressure. How much do you need to eat? The amounts are relatively high.
Eating 570 g (about a pound and a quarter) of vegetables a day will lower your total cholesterol 4% (about 10 points) in a month.
Eating 600 g (a little more than a pound and a quarter) of fresh apples a day can also lower your total cholesterol 4% (about 10 points) in a month, although sometimes the reduction is as much as 11% (about 22 points).
Eating 200 g (about half a pound) of carrots, 100 g (about 2-1/2 oz) of prunes, or 500 g (a little more than a pound) of guava fruit a day can also lower cholesterol 5 to 12%, or about 12 to 25 points, in a month.
Many people with high cholesterol, of course, would prefer to taking a supplement to eating a pound of apples every day. The combination of some fruits and vegetables and a balance vitamin supplement every day is ideal.