Luis Rosero Bixby
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Item A case-control study of breast cancer and hormonal contraception in Costa Rica(JNCI, vol. 7, no. 1 (december 1987), 1987) Lee, Nancy C.; Rosero Bixby, Luis; Oberle, Mark W.; Grimaldo, Carmen; Whatley, Anne S.; Rovira, Elizabeth Z.By 1981, 11% of married women in Costa Rica ages 20-49 years had used depot-medroxyprogesterone acetate (DMPA) and 58% had used oral contraceptives (OCs). Since 1977, the Costa Rican Ministry of Health has maintained a nationwide cancer registry. These circumstances provided an opportunity for a population-based, case-control study of DMPA, OCs, and breast cancer in Costa Rica. Cases were 171 women ages 25-58 years with breast cancer diagnosed between 1982 and 1984; controls were 826 women randomly chosen during a nationwide household survey. Cases and controls were interviewed with the use of a standard questionnaire covering their reproductive and contraceptive histories. Logistic regression methods were used to adjust for confounding factors. While few cases or controls had ever used DMPA, DMPA users had an elevated relative risk (RR) estimate of breast cancer of 2.6 (95% confidence limits = 1.4-4.7) compared with never users. However, no do'se-response relationship was found; even the group of women who had used DMPA for less than 1 year had an elevated RR estimate (RR = 2.3; 95% confidence limits = 1.0-5.1). In contrast, OC users had no elevation in RR compared with never users (RR = 1.2; 95% confidence limits= 0.8-1.8). The results of the DMPA analysis are inconclusive. Before decisions are made on whether to continue providing this effective contraceptive method, other ongoing studies will need to confirm of refute these findings.—JNCI 1987; 79:1247-1254.Item The effect of using different reference dates for control exposure measurement on relative risk estimates in a case-control study(Journal Clinical Epidemiologycal, Vol. 46, no. 5, 1993) Rampey, Alvin H.; Irwin, Kathleen L.; Oberle, Mark W.; Kinchen, Steven; Lee, Nancy C.; Marsden, Anne; Rosero Bixby, LuisArtículo científico -- Universidad de Costa Rica, Instituto de Investigaciones en Saud. 1993. Debido a las políticas de la revista en la que el artículo fue publicado, no es posible distribuir la edición del editor/PDF. In case-control studies in which case and control enrollment periods are not identical, exposure status for time-dependent variables is often measured relative to a reference date. Using data from a case-control study of the relation between cervical cancer and oral contraceptive (OC) use in which control enrollment began 6 months after the end of case enrollment, we evaluated the effect on odds ratios from using five different reference dates to determine the controls' exposure status. The choice of reference date had little effect on the odds ratios in this study. Reference dates for time-dependent exposure variables should be considered carefully in studies when case and control enrollment periods are not identical.Item Estudio longitudinal de mortalidad de adultos costarricenses 1984-2007(Población y Salud en Mesoamérica; Volumen 7, Número 2, 2010) Rosero Bixby, Luis; Antich Montero, DanielSe describen los procedimientos y se presentan algunos resultados del "estudio longitudinal de mortalidad de adultos costarricenses" (ELMAC), consistente en una muestra de cerca de 20.000 costarricenses de 30 o más años de edad del censo de población de 1984 seguidos hasta fines de 2007. El Instituto Nacional de Estadística y Censos (INEC) digitalizó los nombres de la boleta censal de los individuos en la muestra. Procesos informáticos depuraron los nombres y los enlazaron al número único de identificación -el número de cédula- del Registro Civil. El empate se efectuó en el 87% de la muestra. Los individuos identificados se siguieron en las bases de datos del Registro Civil para establecer su sobrevivencia. Se identificaron más de 5.000 defunciones entre el censo de 1984 y diciembre de 2007. Procesos informáticos adicionales enlazaron 92% de estas defunciones con las de las estadísticas vitales del INEC que contienen el dato de la causa de defunción. El patrón de mortalidad de la muestra, que comprende 373.000 personas-años de observación, reproduce bien las tasas de las tablas de mortalidad del país. Las gradientes socioeconómicas de la mortalidad en esta muestra no son sensibles a posibles errores en los empates o en las imputaciones efectuadas. La muestra confirma la excepcionalmente baja mortalidad de los adultos costarricenses, especialmente de los varones. Esta muestra abre la puerta para que se efectúen variedad de análisis de los determinantes socioeconómicos de la mortalidad de adultos en Costa Rica, algo rara vez intentado en un país en desarrollo.Item Longer leukocyte telomere length in Costa Rica's Nicoya Peninsula: A population-based study(Experimental Gerontology; Volumen 48, Número 11, 2013) Rehkopf, David H.; Dow, William H.; Rosero Bixby, Luis; Lin, Jue; Epel, Elissa S.; Blackburn, Elizabeth H.Studies in humans suggest that leukocyte telomere length may act as a marker of biological aging. We investigated whether individuals in the Nicoya region of Costa Rica, known for exceptional longevity, had longer telomere length than those in other parts of the country. After controlling for age, age squared, rurality, rainy season and gender, mean leukocyte telomere length in Nicoya was substantially longer (81 base pairs, p<0.05) than in other areas of Costa Rica, providing evidence of a biological pathway to which this notable longevity may be related. This relationship remains unchanged (79 base pairs, p<0.05) after statistically controlling for nineteen potential biological, dietary and social and demographic mediators. Thus the difference in mean leukocyte telomere length that characterizes this unique region does not appear to be explainable by traditional behavioral and biological risk factors. More detailed examination of mean leukocyte telomere length by age shows that the regional telomere length difference declines at older ages.Item Seasonal variation of peripheral blood leukocyte telomere length in Costa Rica : a population-based observational study(American Journal of Human Biology; Volumen 26, Número 3, 2014) Rehkopf, David H.; Dow, William H.; Rosero Bixby, Luis; Lin, Jue; Epel, Elissa S.; Blackburn, Elizabeth H.Objectives: Peripheral blood leukocyte telomere length (LTL) is increasingly being used as a biomarker of aging, but its natural variation in human populations is not well understood. Several other biomarkers show seasonal variation, as do several determinants of LTL. We examined whether there was monthly variation in LTL in Costa Rica, a country with strong seasonal differences in precipitation and infection. Methods: We examined a longitudinal population-based cohort of 581 Costa Rican adults age 60 and above, from which blood samples were drawn between October 2006 and July 2008. LTL was assayed from these samples using the quantitative PCR method. Multivariate regression models were used to examine correlations between month of blood draw and LTL. Results: Telomere length from peripheral blood leukocytes varied by as much as 200 base pairs depending on month of blood draw, and this difference is not likely to be due to random variation. A moderate proportion of this association is statistically accounted for by month and region specific average rainfall. We found shorter telomere length associated with greater rainfall. Conclusions: There are two possible explanations of our findings. First, there could be relatively rapid month-to-month changes in LTL. This conclusion would have implications for understanding the natural population dynamics of telomere length. Second, there could be seasonal differences in constituent cell populations. This conclusion would suggest that future studies of LTL use methods to account for the potential impact of constituent cell type.Item Predicting survival from telomere length versus conventional predictors: a multinational population-based cohort study(PLOS One; Volumen 11, Número 4, 2016) Glei, Dana; Risques, Rosa Ana; Rehkopf, David H.; Dow, William H.; Rosero Bixby, Luis; Weinstein, Maxine; Goldman, NoreenTelomere length has generated substantial interest as a potential predictor of aging- related diseases and mortality. Some studies have reprted significant associations, but few have tested its ability to discriminate between decedents and survivors compared with a broad range of well-established predictors that include both biomarkers and commonly collected self-reprted data. Our aim here was to quantify the prognostic value of leuko- cyte telomere length relative to age, sex, and 19 other variables for predicting five-year mortality among older persons in three countries. We used data from nationally represen- tative surveys in Costa Rica (N = 923, aged 61+), Taiwan (N = 976, aged 54+), and the U. S. (N = 2672, aged 60+). Our study used a prospective cohort design with all-cause mor- tality during five years post-exam as the outcome. We fit Cox hazards models separately by country, and assessed the discriminatory ability of each predictor. Age was, by far, the single best predictor of all-cause mortality, whereas leukocyte telomere length was only somewhat better than random chance in terms of discriminating between decedents and survivors. After adjustment for age and sex, telomere length ranked between 15th and 17th (out of 20), and its incremental contribution was small; nine self-reprted variables (e.g., mobility, global self-assessed health status, limitations with activities of daily living, smoking status), a cognitive assessment, and three biological markers (C-reactive protein, serum creatinine, and glycosylated hemoglobin) were more powerful predictors of mortality in all three countries. Results were similar for cause-specific models (i.e., mortality from cardiovascular disease, cancer, and all other causes combined). Leukocyte telomere length had a statistically discernible, but weak, association with mortality, but it did not predict survival as well as age or many other self-reprted variables. Although telomere length may eventually help scientists understand aging, more powerful and more easily obtained tools are available for predicting survival.