Am Fam Physician. 2004;70(3):559-560
Case Study
JB, a 35-year-old smoker, comes to your office for a well-woman examination. Reviewing her medication list, you learn that she is taking numerous vitamin supplements, including vitamins A, C, E, and beta-carotene. JB has read that these vitamins help prevent heart disease and cancer. She asks if taking vitamins will prevent these conditions.
Case Study Questions
Which one of the following statements about the U.S. Preventive Services Task Force (USPSTF) recommendations on routine vitamin supplementation to prevent cancer and cardiovascular disease is correct?
A. The USPSTF recommends the use of supplements of vitamins C and E for the prevention of cancer or cardiovascular disease.
B. The USPSTF found insufficient evidence to recommend for or against the use of supplements of vitamins A, C, or E; multivitamins with folic acid; or antioxidant combinations for the prevention of cancer or cardiovascular disease.
C. The USPSTF does not recommend the use of supplements of vitamins A, C, or E; multivitamins with folic acid; or antioxidant combinations for the prevention of cancer or cardiovascular disease.
D. The USPSTF recommends the use of beta-carotene supplements, either alone or in combination, for the prevention of cancer or cardiovascular disease.
E. The USPSTF found insufficient evidence to recommend for or against the use of beta-carotene supplements, either alone or in combination, for the prevention of cancer or cardiovascular disease.
2. Which one of the following statements about beta-carotene supplements for cancer and cardiovascular disease prevention is correct?
A. Beta-carotene supplementation is more effective in middle-aged and older smokers than in younger smokers.
B. Beta-carotene supplementation is more effective in light smokers than in heavy smokers.
C. Beta-carotene supplementation is more effective in female smokers than in male smokers.
D. Beta-carotene supplementation in smokers is more effective in preventing cardiovascular disease than in preventing lung cancer.
E. Beta-carotene supplementation in heavy smokers is associated with a higher incidence of lung cancer and higher all-cause mortality.
3. Which of the following counseling messages should you consider for JB?
A. Dietary supplements may be appropriate if your diet does not provide the recommended intake of specific vitamins.
B. Some vitamins may be harmful in high dosages.
C. If you take vitamins, the higher the dosage, the better.
D. Avoid foods that contain naturally occurring beta-carotene.
Answers
1. The correct answer is B. The USPSTF found poor evidence to determine whether supplementation with vitamins A, C, or E; multivitamins with folic acid; or antioxidant combinations reduce the risk for cardiovascular disease or cancer. The evidence from randomized trials is inadequate or conflicting, and the influence of confounding variables on observed outcomes in observational studies cannot be determined. As a result, the USPSTF could not determine the balance of benefits and harms of routine use of these supplements for the prevention of cancer or cardiovascular disease.
The USPSTF found good evidence that beta-carotene supplements, alone or in combination, provide no benefit in the prevention of cancer or cardiovasular disease in middle-aged and older adults. This lack of important benefits, combined with potential harms in some groups (see below), led the USPSTF to recommend against beta-carotene supplementation for cancer or cardiovascular disease prevention.
2. The correct answer is E. In two randomized clinical trials restricted to heavy smokers, beta-carotene supplements were associated with higher incidence of lung cancer and higher all-cause mortality. Good existing evidence showed that beta-carotene supplements provide no benefit for cancer or cardiovascular disease prevention in middle-aged and older adults.
3. The correct answers are A and B. With the exception of vitamins for which there is compelling evidence of net harm (e.g., beta-carotene supplements in smokers), there is little reason to discourage people from taking vitamin supplements. Taking supplements does not replace the need to eat a healthy diet, although supplements may be appropriate for people whose diet does not provide the recommended daily allowance of specific vitamins. Some vitamins, such as vitamins A and D, may cause harm in high dosages. Therefore, people who choose to take vitamins should be encouraged to adhere to the recommended daily allowances. There is no evidence that beta-carotene is harmful to smokers at levels occurring naturally in foods.
Sources
U.S. Preventive Services Task Force. Routine vitamin supplementation to prevent cancer and cardiovascular disease: recommendations and rationale. Ann Intern Med 2003;139:51–5.
Morris CD, Carson S. Routine vitamin supplementation to prevent cardiovascular disease: a summary of the evidence for the U.S. Preventive Services Task Force. Ann Intern Med 2003;139:56–70.
Ritenbaugh C, Streit K, Helfand M. Routine vitamin supplementation to prevent cancer: a summary of the evidence from randomized controlled trials for the U.S. Preventive Services Task Force. Accessed May 18, 2004, at: http://www.ahrq.gov/clinic/3rduspstf/vitamins/vitasum.htm.
Atkins D, Shetty P. Routine vitamin supplementation to prevent cancer: update of the evidence from randomized controlled trials, 1999–2002. Accessed May 18, 2004, at: http://www.ahrq.gov/clinic/3rduspstf/vitamins/vitupdate.htm.