Many studies support the use of nutritional supplements to achieve sufficient levels of nutrients. Raymond Shamberger and Derrick Lonsdale, researchers  from the Cleveland Clinic (Ohio), found out that the empty-calorie diets can lead to such problems as lassitude, fatigue, mood swings, insomnia, and other health complaints. They studied patients who were given supplementary nutrients over a period of six to twelve weeks, and came to conclusion that many of their symptoms improved.

  Ruth Harrell, David Benton, and Guilyn Roberts at the University of Wales, studied children suffering from marginal nutrient deficiency. They found out that the administration of multivitamin supplements essentially improved their health. The same notice was taken in studying the mental capacity of elderly individuals.

  Current studies revealed that vitamin C can slow the development of cataracts, heart disease, and cancer. James E. Enstrom, M.D., an epidemiologist at the University of California at Los Angeles, discovered that men who consume vitamin C every day, at levels 500 to 666 percent of the U.S. RDA, live about six years longer than men who don't.

  Robert Cathcart, M.D., of Los Altos, California, has also documented the effective use of vitamin C in treating various infectious diseases, including the common cold, flu, pneumonia, hepatitis, mononucleosis, and several childhood diseases.

  Other clinical studies have shown that  low intakes of beta-carotene (pro-vitamin A), vitamin E, and vitamin C can heighten incidences of cancer. Research done at Johns Hopkins University found that there were about 50 percent fewer heart disease cases in a group of people with the highest levels of beta-carotene, compared to the group with the lowest levels. The same study at Harvard University found that of two groups with prior evidence of heart disease, the group given a beta-carotene supplement had 40 percent fewer heart attacks than the group given a placebo.

  Research has also found that vitamin B₃ (niacin) can help combat heart disease, while vitamin B₆ can help prevent atherosclerosis.

  Other studies have shown the same results with vitamin E and heart disease. Large doses of vitamin E help to strengthen immune functioning and reduce the severity of age-related diseases such as Parkinson's disease.

  Eric Braverman, M.D., of New Jersey, suggested to use amino acid supplementation  to treat heart disease, as well as herpes, alcoholism, and a variety of psychiatric disorders. Zinc supplementation helps to improve progressive hearing loss and other related ear problems.

  Bioflavonoids, which present in citrus rind and buckwheat, were found to help to increase vitamin C's antiviral activity in treating herpes simplex. Coenzyme Q10 helps to improve heart function, and gamma-linolenic acid may help to regulate the cardiovascular, nervous, and immune systems of the body.

  In addition to disease control, nutritional supplements can also help people withstand  specific lifestyle, environmental, and emotional/ psychological factors. For example, smokers require more vitamin E, vitamin C, and beta-carotene than nonsmokers, and persons who consume a significant amount of alcohol require more vitamin B₁ and magnesium than the average person.

  Dr. Berkson says that individuals engaged in heavy exercise programs need to make sure they are getting sufficient nutrients because their caloric demands will increase. Weight-loss dieters also need supplemental vitamins and minerals to fill up the deficiencies that result from reduced calorie intake. 

  Women taking oral contraceptives may need to increase their zinc, folic acid, and vitamin B₆ intakes, while pregnant women may require more folic acid for proper fetal development. Lactating women also need additional magnesium and protein, and postmenopausal women require increased calcium and vitamin D to keep up strong bones.

  When recovering from surgery, a person may need higher levels of zinc, and individuals unprotected to smog or other pollutants require higher levels of the protector nutrients such as selenium, vitamin E, and vitamin C. Persons who are under heavy emotional or physical stress will need higher intakes of all the B vitamins.