Vitamins can help prevent disease in two main ways: By preventing the deficiency syndromes characteristic of the respective vitamin, and through the health benefits conferred by that specific vitamin. For example, Vitamin A is important for our vision. It also plays a major role in bone growth, reproduction, cell division and cell differentiation. It helps maintain the surface linings of the eyes and the respiratory, urinary, and intestinal tracts. When those linings break down, bacteria can enter the body and cause infection.

Vitamin A also helps maintain the integrity of skin and mucous membranes that function as a barrier to bacteria and viruses. Vitamin A helps in part to regulate the immune system. The immune system helps prevent or fight off infections by making white blood cells that destroy harmful bacteria and viruses. Vitamin A appears to help lymphocytes, a type of white blood cell that fights infections, function more effectively.

Your body needs calcium to build and maintain strong bones and teeth. You must absorb calcium every day from your dietary intake because your body does not and cannot make calcium. You lose calcium through shed skin, nails, hair, sweat, urine and feces. When you do not have enough calcium, your body breaks down bone to obtain this mineral. A good liquid multivitamin will provide you with the amount of calcium you need, as well as many other essential vitamins and minerals.

Bones are constantly going through a process known as remodeling in which small amounts of old bone are removed and new bone is formed in its place. Generally, after age 35, more bone is lost than gained. Bone loss accelerates after menopause and this can lead to osteoporosis.

Women (but men are certainly not immune) are especially vulnerable to osteoporosis, or a thinning of the bones, which develops slowly over many years. Researchers believe that decreasing hormone levels, too little calcium in the diet early in life, and lack of exercise all play a role in osteoporosis. One of the advances that changed the way we look at vitamins is the discovery that too little folic acid, one of the eight B vitamins, is linked to birth defects such as spina bifida and anencephaly. Fifty years ago, no one knew what caused these birth defects, which occur when the early development of tissues that eventually become the spinal cord and the tissues that surround it go awry.

Twenty five years ago, British researchers found that mothers of children with spina bifida had low vitamin levels. Eventually, two large trials in which women were randomly assigned to take folic acid or a placebo showed that getting too little folic acid increased a woman's chances of having a baby with spina bifida or anencephaly and that getting enough folic acid could prevent these birth defects.

Enough folic acid, at least 400 micrograms a day, isn't always easy to get from food. That's why women of childbearing age are urged to take extra folic acid. It's also why the US Food and Drug Administration now requires that folic acid be added to most enriched breads, flour, cornmeal, pastas, rice, and other grain products, along with the iron and other micronutrients that have been added for years. However, this often is not enough to ensure adequate intake of folic acid as people have a wide vareity of eating habits.

The other exciting discovery about folic acid and two other B vitamins is that they may help fight against some types of cancer. It's too early to tell if there's merely an association between increased intake of folic acid and other B vitamins and heart disease or cancer, or if high intakes prevent these chronic diseases. In 1968, a Boston pathologist investigating the deaths of two children from massive strokes wondered if the high levels of a protein breakdown product called homocysteine in their systems could have been the reason their arteries were as clogged with cholesterol as those of a 55-year-old fast food addict. Bottom line is that high levels of homocysteine are to be avoided at all costs, and folic acid is a very good way to help to minimize your homocysteine levels.

Since then, many studies have linked high levels of this breakdown product, called homocysteine, with increased risks of heart disease and stroke. Folic acid, vitamin B6, and vitamin B12 play key roles in recycling homocysteine into methionine, one of the 20 or so building blocks from which the body builds new proteins. Without enough folic acid, vitamin B6, and vitamin B12, this recycling process becomes inefficient and homocysteine levels increase, increasing your risk of heart disease dramatically.

Several observational studies show that high levels of homocysteine are associated with increased risks of heart disease and stroke. Increasing intake of folic acid in particular, vitamin B6, and vitamin B12 decreases homocysteine levels. And some observational studies show lower risks of cardiovascular disease among people with higher intakes of folic acid, those who use multivitamin supplements, or those with higher levels of serum folate (the form of folic acid found in the body).

Ongoing randomized trials, such as the Women's Antioxidant Cardiovascular Study and the Vitamin Intervention in Stroke Prevention Study should yield more definitive answers regarding homocysteine, B vitamins, and cardiovascular risk.

In addition to recycling homocysteine, folate plays a key role in building DNA, the complex compound that forms our genetic blueprint. Observational studies show that people who get higher than average amounts of folic acid from their diets or supplements have lower risks of colon cancer and breast cancer.

This could be especially important for those who drink alcohol, since alcohol blocks the absorption of folic acid and inactivates circulating folate. An interesting observation from the Nurses' Health Study is that high intake of folic acid blunts the increased risk of breast cancer seen among women who have more than one alcoholic drink a day. Our cells must constantly contend with nasty substances called free radicals. These free radicals can damage DNA, the inside or artery walls, proteins in the eye - just about any substance or tissue imaginable. Some are made inside the body, inevitable byproducts of turning food into energy. Others come from the air we breathe and the food we eat. Still others come from contamination from toxins.

We aren't defenseless against free radicals. We extract free radical fighters, called antioxidants, from food. Fruits, vegetables, and other plant-based foods deliver dozens, if not hundreds, of antioxidants. The most common are vitamin C, vitamin E, beta-carotene and related carotenoids. Food also supplies minerals such as selenium and manganese, which are needed by enzymes that destroy free radicals. During the 1990s, the term antioxidants became a huge nutritional buzz word. They were promoted as wonder agents that could prevent heart disease, cancer, cataracts, memory loss, and a host of other conditions.

It's true that the package of antioxidants, minerals, fiber, and other substances found in fruits, vegetables, and whole grains help prevent a variety of chronic diseases. Recent research evidence suggest high doses of vitamins C, E, and other antioxidants can accomplish a similar feat in people who either do not get the required levels of antioxidants in their diet (most don't) or have poor absorption of vitamins in the first place.

A good multivitamin is the foundation of health and nutrition. Take a look at our scientific reviews of many of the popular brands for factors such as ingredients, areas of improvement, quality level, and overall value. If you are looking for a high quality liquid multivitamin, we suggest that you take a look at the Multivitamin Product Comparisons.

References
1. World Cancer Research Fund. Food, Nutrition and Cancer. Washington, DC: American Institute for Cancer Research, 1997.

2. Feskanich D, Singh V, Willett WC, Colditz GA. Vitamin A intake and hip fractures among postmenopausal women. JAMA 2002; 287:47-54.

3. Rothman KJ, Moore LL, Singer MR, Nguyen US, Mannino S, Milunsky A. Teratogenicity of high vitamin A intake. N Engl J Med 1995; 333:1369-73.

4. Smithells RW, Sheppard S, Schorah CJ. Vitamin dificiencies and neural tube defects. Arch Dis Child 1976; 51:944-50.

5. Federal Register. Food Standards: Amendment of Standards of Identity For Enriched Grain Products to Require Addition of Folic Acid. Final rule, 5 March 1996. Food and Drug Administration: Washington, DC, 1996.

6. McCully KS. Vascular pathology of homocysteinemia: implications for the pathogenesis of arteriosclerosis. Am J Pathol 1969; 56:111-28.