Those who believe vitamins and minerals guard against chronic disease base their argument on the deficient or suboptimal diets of the young, the elderly and those who have poor dietary habits. Because these groups of people tend to have diets lacking in fruits, vegetables and dairy products, supplementation may prevent nutritional deficiencies and reduce the risk of heart disease, osteoporosis and some cancers. In addition, multivitamins are considered safe when taken as directed and provide an inexpensive means of nutritional insurance.
Critics, on the other hand, believe supplementation may do more harm than good and think more evidence is needed before making any recommendations. Increasing the amounts of particular supplements in one's diet does not guarantee additional benefits beyond what's normally found in food. One notable study, Beta-Carotene and Lung Cancer: A Case Study published in the American Journal of Clinical Nutrition, showed how beta-carotene supplementation actually increased the risk of lung cancer in male smokers. The combination of micronutrients found within foods may be more efficacious to one's health than the particular vitamins themselves. Furthermore, most of the classic diseases within the past one hundred years (i.e., scurvy, rickets, beriberi, and pellagra) have been eradicated without vitamin supplementation due to the fortification of many foods and a greater amount of foods available via transportation.
One particular study I found supported the view that vitamins help prevent chronic disease. The study, entitled Folate, Vitamin B6, and B12 Intakes in Relation to Risk of Stroke Among Men, supports the intake of folate and vitamin B12 in reducing the risk of ischemic stroke in men. The study, lasting fourteen years, investigated 43,732 men between the ages of 40 and 75 years old. Evidence was obtained using detailed questionnaires dealing with medical history, lifestyle and diet. Additional questionnaires were mailed periodically to assess health history and diet of each participant. Confounding factors such as age, smoking history, BMI, physical activity level, medication usage, alcohol, and supplement intakes were also controlled. The level of homocysteine, an indicator of cardiovascular disease risk, within the blood of each participant was studied before and after prolonged intakes of these vitamins. The result was that those individuals who consumed increasing amounts of folate and vitamin B12 showed lowered homocysteine levels. Reduced homocysteine levels are indicative of a decreased risk of ischemic stroke.
On the other hand, two other studies that were examined did not support the view that vitamins help prevent chronic disease. The researchers in one study, entitled Lack of Long-Term Effect of Vitamin C Supplementation on Blood Pressure, discovered no reduction in blood pressure with a moderate (500 mg/day) intake of vitamin C. The study, lasting five years, investigated only 244 Japanese men and women between the ages of 40 and 69 years old. Evidence was obtained by trained nurses who measured each participant's blood pressure using a sphygmomanometer. Participants provided information on their weight, height, smoking status, alcohol consumption, antihypertensive medication, disease history, and general health status. The participants also completed a Food Frequency Questionnaire (FFQ) to provide information on their food habits at enrollment of the trial and after the fifth year. Fasting blood samples were collected at the beginning of the trial and after the fifty year to determine vitamin C levels. It was found that systolic blood pressure was significantly increased after long-term vitamin C supplementation. The confounding factors mentioned above, with the exception of antihypertensive medication, may not have been adequately controlled. In addition, the sample size and study duration may have been inadequate to provide a firm conclusion.
The other study, entitled Effect of alpha-tocopherol and beta-carotene supplementation on coronary heart disease during the 6-year post-trial follow-up in the ATBC study, found no evidence to support that vitamin E and beta-carotene reduced the risk of heart disease. The original study, lasting up to eight years, used a sample of 29,133 male smokers between the ages of 50 and 69 years old. The six year follow-up of the ATBC study revealed that beta-carotene seemed to increase the risk of non-fatal myocardial infarction in the smokers. Evidence was obtained when the participants reported to the study center. Information such as smoking history, cholesterol levels, blood pressure, height, and weight were collected. The confounding factors mentioned above may also not have been adequately controlled.
I have found during my research of this controversial issue that clinical evidence supporting the intake of vitamins and mineral supplements in preventing chronic disease is not very plentiful. One major problem in studying how vitamins may prevent chronic disease is the time frame required to observe results. Prospective analysis takes years to establish definitive evidence supporting a particular vitamin's beneficial effects on the human body. It is impractical and inconvenient to expect participants to partake in a study lasting ten or more years without some unintended consequences (i.e., death, impaired health, etc.).
A large sample of relatively healthy participants is needed to provide ample verification of the effects observed. Also, many confounding variables must be controlled to eliminate as much of possibility of data contamination. The more variables involved, the larger the sample of participants needed to compensate. The stroke and heart disease studies each had relatively large sample sizes, whereas the hypertension study had too small of a sample size. In addition, the stroke study seemed to adequately control its variables as mentioned in the literature whereas this may not have been the case in the hypertension and heart disease studies.
Research is mixed when it comes to the evidence concerning whether or not vitamins and minerals help prevent chronic disease. It was revealed that folate and vitamin B12 may reduce the risk of ischemic stroke, but that vitamin C does not reduce the risk of hypertension and vitamin E and beta-carotene do not reduce the risk of heart disease. Given the inconsistent evidence of how particular micronutrients may be useful in supporting one's health, I feel it's more prudent and feasible to supplement with a good, comprehensive multivitamin rather than with particular vitamins and minerals. I believe that children, the elderly and those individuals eating a poor diet should supplement with a multivitamin as a means of nutritional insurance against chronic disease risk.
Brian Danley, CFT
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