Showing papers by "Margaret R. Karagas published in 1997"

Mortality Associated with Low Plasma Concentration of Beta Carotene and the Effect of Oral Supplementation

Abstract: OBJECTIVE To examine the relationship between beta carotene plasma concentration and beta carotene supplementation and risk of death from major disease causes. DESIGN Cohort study of plasma concentrations; randomized, controlled clinical trial of supplementation. SETTING Medical school-affiliated dermatology practices. PATIENTS A total of 1188 men and 532 women with mean age of 63.2 years, who had enrolled in a randomized clinical trial of beta carotene supplementation to prevent nonmelanoma skin cancer. INTERVENTION Oral beta carotene, 50 mg per day for a median of 4.3 years. MAIN OUTCOME MEASURES All-cause mortality and mortality from cardiovascular disease and cancer. RESULTS During a median follow-up period of 8.2 years, there were 285 deaths. Persons whose initial plasma beta carotene concentrations were in the highest quartile (>0.52 micromol/L [27.7 microg/dL]) had a lower risk of death from all causes (adjusted relative rate [RR], 0.52; 95% confidence interval [CI] 0.44 to 0.87) and from cardiovascular diseases (adjusted RR, 0.57; 95% CI, 0.34 to 0.95) compared with persons with initial concentrations in the lowest quartile (<0.21 micromol/L [11.2 microg/dL]). Patients randomly assigned to beta carotene supplementation showed no reduction in relative mortality rates from all causes (adjusted RR, 1.03; 95% CI, 0.82 to 1.30) or from cardiovascular disease (adjusted RR, 1.16; 95% CI, 0.82 to 1.64). There was no evidence of lower mortality following supplementation among patients with initial beta carotene concentrations below the median for the study group. CONCLUSIONS These analyses provide no support for a strong effect of supplemental beta carotene in reducing mortality from cardiovascular disease or other causes. Although the possibility exists that beta carotene supplementation produces benefits that are too small or too delayed to have been detected in this study, noncausal explanations should be sought for the association between plasma concentrations of beta carotene and diminished risk of death.

Risk of squamous cell carcinoma of the skin in relation to plasma selenium, alpha-tocopherol, beta-carotene, and retinol: a nested case-control study.

Abstract: We conducted a nested case-control study of squamous cell skin cancer (SCC) to determine whether risk was related to plasma concentrations of selenium, alpha-tocopherol, beta-carotene, and retinol. We derived the study sample from participants in our Skin Cancer Prevention Study, all of whom had at least one basal cell or squamous cell skin cancer before study entry. Those who developed a new squamous cell skin cancer during the 3-5-year follow-up period were selected as cases (n = 132). Controls (n = 264) were chosen at random, with matching by age, sex, and study center, from among those who did not develop SCC but were being followed actively at the time the SCC case was diagnosed. Prediagnostic plasma samples were analyzed for alpha-tocopherol, beta-carotene, and retinol using high-performance liquid chromatography. Selenium determinations were made using instrumental neutron activation analysis. Odds ratios were computed using conditional logistic regression for matched samples. We found no consistent pattern of SCC risk associated with any of the nutrients examined. The odds ratios (95% confidence intervals) for the highest versus the lowest quartiles of beta-carotene, retinol, alpha-tocopherol, and selenium were 0.73 (0.38-1.41), 1.43 (0.77-2.64), 0.89 (0.43-1.85), and 0.86 (0.47-1.58), respectively. Thus, our data add to the growing body of evidence that these nutrients, at the concentrations we evaluated, are not related strongly to SCC risk.

Rarity of Human Papillomavirus in Nonmelanoma Skin Cancer among Immunocompetent Patients

Abstract: Background: The role of human papillomavirus (HPV) in nonmelanoma skin cancer (NMSC) among immunocompentent individuals is not well understood. Objective: We tested for the presence of HPV DNA in NMSC of immunocompetent patients from New England. Methods: Biopsies taken from 59 patients were reviewed histopathologically. A segment of the biopsy and scrapings from a site remote from the skin lesion were analyzed for HPV using a standardized polymerase chain reaction (PCR) DNA amplification assay. Results: Of 55 evaluable samples, 21 were histologically confirmed squamous cell carcinomas (SCC), 25 were basal cell carcinomas (BCC), and nine had other diagnoses. Two samples were HPV-positive (3.6%): a basal cell carcinoma of the forehead and a squamous cell carcinoma of the thumbnail bed. Type analysis of these samples revealed HPV 16 from both lesions. Conclusion: The HPV DNA is not commonly detected in NMSCs of immunocompetent patients using standard laboratory techniques. It is possible, however, that a wider range of HPV types could be detected using more sensitive assays; this warrants further investigation.

When Subjects are Not Randomly Assigned: The Cohort Approach

Abstract: Background: Cohort studies are often used to answer clinical and etiologic questions. Objective: This article is to provide an overview of the basic concepts of cohort studies that are pertinent to the evaluation of the published literature. Methods: Fundamental principles, methods of assessing exposure and outcome status, choice of a comparison group, and statistical methods used in cohort studies are reviewed. Studies focusing on skin neoplasms are used as examples. Results: Methods used in cohort studies are similar to those used in clinical trials. One of the distinguishing features is that the exposure (e.g., treatment) is observed rather than assigned by the study investigators. Therefore, an effort must be made to ensure comparability between exposed and unexposed groups. Conclusion: Cohort studies have provided valuable clinical and etiologic information, but the strengths and limitations of this approach need to be recognized when evaluating the literature.