Written for General Chemistry Chemistry 109, Professor Andersson
Abstract: In the past few years, there has been much controversy about the effects of beta-carotene on the human body. Beta-carotene is an essential factor in the diet of all humans because it is an antioxidant and a precursor for Vitamin A, which the body needs in order to properly function. It was once believed that beta-carotene was a possible deterrent of heart disease and cancer. There are recent studies which have proven that individuals with high levels of beta-carotene in their blood derived from proper nutrition (not from supplements) have much lower rates of cancer and heart disease than those with poorer diets. However, recent studies have also proven that beta-carotene supplements may actually increase the risk of heart disease and/or cancer in individuals who are at a higher than normal risk for obtaining these diseases, such as smokers and asbestos workers. Evidence obtained from various studies strongly suggests that supplemental beta-carotene increases the rate of lung cancer by 28% and heart disease by 17% in high-risk individuals. Although there may be adverse effects from taking supplemental beta-carotene for these individuals, studies have concluded that average and low-risk individuals will receive either positive or no effects from the supplements. Some scientists believe that there may be some component of cigarette smoke that reacts with beta-carotene to produce pro-oxidants, while others believe that it may be carotene that is harmful when it is abstracted from supplements. It may be that the positive effects shown by those whose diets are rich in beta-carotene are due to an interaction of beta-carotene and one or some of the 600 other carotenoids that can be found in vegetables and fruits. Yet, an alternate hypothesis suggests that it is not beta-carotene at all that is involved in the deterrence of heart disease and cancer. Therefore, it is in the best interest of consumers not to buy beta-carotene supplements, but to ensure that they eat many different vegetables and fruits along with a proper diet.
1. Foltz-Grey, Dorothy. "Squash: As Good as Gold," Health, January/ February, 1997,pp. 30-35. 2. Rowe, Paul M. "Beta Carotene takes a Collective Beating," The Lancet, Jan 27, 1996, vol. 347, p. 249.
Chemical Impact: I chose beta-carotene to be the focus of this paper because it is the cause of much controversy amongst doctors, scientists, nutritionists, and "health-nuts". Too many people are preoccupied with finding new and easy ways to improve their health. The latest health fad of the 1990's involves vitamins and supplements. There are many people who believe that a poor diet can be ignored if it's supplemented with "magic pills". The fact of the matter is that a healthy diet and lifestyle is essential to the welfare of any being. Above all, because it is only a recent trend that so many people have been "popping" these magic pills, the effects of these pills are still relatively unknown, as is the case for beta-carotene supplements. Some people use supplements as an excuse or crutch so that they can continue engaging in unhealthy activities such as smoking and drinking. People may potentially be harming their bodies, all for the sake of avoiding healthy foods and exercise. It is important to know what we are putting into and doing to the bodies that will be with us for the rest of our earthly lives.
Chemistry of Beta-Carotene: The formula of the beta-carotene molecule is C40 H56 and the molecular weight of the molecule is 536.88amu, of which 89.49% is composed of carbon, and 10.51% is hydrogen(7). Beta-carotene is built symmetrically with strings of carbon atoms containing two identical beta rings at each end, resulting in a non-polar molecule(8). (See Figure 1.) Beta carotene is practically insoluble in water, acids, and alkalines, but moderately soluble in ethers and oils(7). It is also a precursor to Vitamin A(retinol), a fat-soluble vitamin stored in the liver(9). Beta-carotene is cleaved into two identical retinol molecules during digestion in the human body(1). (See Figure 2.) However, the conversion of beta-carotene to retinol in the human body is rarely ever 100%(9). Therefore, the potential potency of Vitamin A in foods appears to be much more than what the body actually produces during digestion. "The potency of Vitamin A in foods is expressed in terms of retinol equivalents: 1mg(one microgram) of retinol=6mg of beta carotene"(9). Beta-carotene is also known to be an antioxidant, a substance that works against oxidation(5). In the body, certain molecules, called free radicals, lack an electron. These molecules are normally produced by the body during metabolic activity, such as respiration. Too many free radicals can result in problems for body cells because they can potentially "prey" upon the molecules of healthy cells by oxidizing them, in order to obtain the missing electron(5). Oxidation damages the cell, and enough damage to many cells can eventually lead to cancer(5).
Figure 1. Structure of Beta-Carotene:
Figure 2. Structure of Vitamin A(Retinol):
During the past few years, there has been much debate about the possible benefits and/or possible adverse effects of beta carotene, a yellowish pigment(one of 600 carotenoids) found in many different fruits and vegetables such as carrots, broccoli, squash, and cantaloupe. Beta Carotene serves as a very important component in the human diet because it is an antioxidant which rids the body of free radicals, and also is also the precursor to Vitamin A(retinol), essential to the health of every human. Since the human body is incapable of making Vitamin A by itself, it is vital that every human obtain it from other sources, or manufacture it by ingesting other substances like beta-carotene which will break down in the body to form Vitamin A. A diet rich in beta-carotene is believed to be beneficial, possibly reducing risks of cancer and lung disease. However, recent evidence has shown that beta carotene obtained through the ingestion of supplements containing concentrated amounts of the carotenoid has no affect on individuals at low risk for cancer and heart disease, but could be detrimental to current and former smokers, as well as asbestos workers. A significant amount of evidence supporting the possibility of beta-carotene's benefits does exist. Regina Ziegler, a nutritional epidemiologist with the National Cancer Institute claimed that "more than 200 studies have shown that diets high in vegetables and fruits are associated with less risk of cancer and heart disease(1). Other evidence has shown that people with higher blood levels containing beta-carotene are also at lower risks for cancer and heart disease(2). After the release of new information pertaining to the possible adverse affects of beta-carotene supplements, in 1996, a study called the Beta-Carotene and Retinol Efficacy Trial (Caret), was performed over a 21 month period. This study used relatively healthy individuals whose blood levels were already high in beta-carotene due to healthy diets, without the use of any supplements. In the CARET study, the individuals were given beta-carotene supplements in addition to their normal diet. The results of the study concluded that these individuals had lower than average rates of cancer and heart disease(2). Although for most individuals it appears that beta-carotene produces favorable effects, on others the effects may be hazardous to their health. The CARET study, before it was performed on relatively healthy individuals, was performed on 18,000 U.S. men and women smokers and asbestos workers. That study concluded that beta-carotene supplements for these individuals resulted in a 28% increase of lung cancer and a 17% increase in death(2). Previous to the CARET study, the 1994 Alpha-tocopherol and Beta-carotene(ATBC) study was performed on 29,000 Finnish male smokers. The results of the ATBC study showed an 18% increase in lung cancer and an 8% increase in death in the individuals involved in the study(2). In January of 1994, three additional large studies about the effects of beta-carotene were released at the National Cancer Institute Conference. These studies found that high daily doses of 20-30 milligrams of beta-carotene supplements(equivalent to the amount found in 4-6 carrots) had no affect on the rates of heart disease and cancer in non-smoking individuals. (Recommended daily dose of beta-carotene for the average male is 6 milligrams(3).) However, it was also concluded that the risk for lung cancer and heart disease did increase in that of current smokers and men who had been exposed to a significant amount of asbestos(3). Contrary to the evidence presented by The National Cancer Institute was found by the Physicians health Study performed in 1995. In this particular study, 22,000 U.S. male physicians were given supplemental beta-carotene and the results showed no evidence of increased death or disease, even in the 11% of the physicians who smoked(2). Due to the strong evidence found in the past few years, supporting both the possible adverse and positive effects of beta-carotene, the complicated nature of this carotenoid is still being investigated. Some scientists and researchers believe that beta-carotene only works to fight off cancer and heart disease in the presence of, or in conjunction with another nutrient found in the fruits and vegetables from which beta-carotene is naturally extracted, like chlorophyll(4). However, other scientists, such as Regina Ziegler, believe that it may not be beta-carotene at all that helps to prevent heart disease and cancer, but some other nutrient found along with beta-carotene in most vegetable and fruits(1 and 4). After all, there are hundreds of other carotenoids that can be found in fruits and vegetables. Julie Burnin, a principle investigator of the Physician's Health Study and the principle investigator in the Women's Health Study, says that people with high amounts of beta-carotene in their blood are at lower risks for heart disease and lung cancer. However, Burnin speculates that this tendency may be due to the fact that well-nourished individuals are possibly more inclined to engage in activities that would promote their health while avoiding those that would hinder it(2). Other scientists believe that beta-carotene in excess may stop acting as an antioxidant and can become pro-oxidantal(1). (Free radicals are oxygen molecules in need of an electron that raid body cells in order to obtain that missing electron(5). ) "According to Dr. James Olson of Iowa State University, under certain conditions, antioxidants can actually promote the development of free radicals"(6). Dr. Olson speculates that the daily use of large dosages of beta-carotene may actually inhibit the absorption of other nutrients that could result in the an excess of free radicals which could induce cancer(6). As for smokers, "Norman Krinsky, a Ph.D. and beta-carotene expert at Tufts University School of Medicine, believes that there may be some component of cigarette smoke that interacts with beta-carotene to produce harmful by-products in the body that would lead to higher rates of lung cancer and heart disease"(4). In light of all the information concerning the possible effects of beta-carotene, this carotenoid most likely has no effect on well-nourished, healthy individuals when taken as supplements. Beta-carotene's possible prevention cancer and heart disease is probably due to the proper balance of nutrients found along with beta-carotene in fruits and vegetables. It is also acceptable to take multivitamins containing no more than the Recommended Daily Allowance value of beta-carotene, (150%),(3). Therefore, it can be seen as a waste of money for one to buy supplements(beta-carotene or Vitamin A) when a healthy diet produces the same effects or even better. People at high risk for cancer and heart disease, such as smokers, people who live with smokers, asbestos workers, those with fatty diets, and alcoholics, should definitely think twice about taking beta-carotene supplements since the effects could be quite hazardous(5).
References: 1. Foltz-Grey, Dorothy. "Squash: As Good as Gold," Health, January/ February, 1997,pp. 30-35. 2. Rowe, Paul M. "Beta Carotene takes a Collective Beating," The Lancet, Jan 27, 1996, vol. 347, p. 249. 3. Anonymous author. "Clueless about Beta-Carotene?" Prevention, May, 1996, vol. 48, pp. 68-69. 4. Anonymous author. "The Trials of Beta-Carotene: Is the Verdict In?" Tufts University Diet & Nutrition Letter, March 1996, vol. 14, pp. 4-7. 5. Norvell, Candyce. "Have You Had Your Antioxidants Today?" Current Health, April 1995, vol. 21, pp. 23-26. 6. Spencer, Peter. "Can Vitamins Cause Cancer?" Consumers' Research Magazine, May 1996, vol. 79, p. 43. 7. Budavari, Susan, ed. Merck Index. Whitehouse Station, NJ: Merck & Co, Inc., 1996, pp. 303-304. 8. Urich, Klaus. Comparative Animal Biochemistry. New York: Springer-Verlag Co., 1994, pp. 728-729. 9. Devlin, Thomas M. Textbook of Biochemistry with Clinical Correlations, 3rd ed. New York: Wiley-Liss, Inc., 1992, pp. 1118-1119. 10. Bhagaran, N.V. Medical Biochemistry. Boston: Jones & Bartlett Publishers, Inc., 1992, pp. 887-889. Articles are copyrighted by their authors. They may not be redistributed in whole or in part without prior written permission. You may make copies for your own private use, but include this copyright notice and proper attribution to the author.
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