Application of the Bayesian dynamic survival model in medicine.

The Bayesian dynamic survival model (BDSM), a time-varying coefficient survival model from the Bayesian prospective, was proposed in early 1990s but has not been widely used or discussed. In this paper, we describe the model structure of the BDSM and introduce two estimation approaches for BDSMs: the Markov Chain Monte Carlo (MCMC) approach and the linear Bayesian (LB) method. The MCMC approach estimates model parameters through sampling and is computationally intensive. With the newly developed geoadditive survival models and software BayesX, the BDSM is available for general applications. The LB approach is easier in terms of computations but it requires the prespecification of some unknown smoothing parameters. In a simulation study, we use the LB approach to show the effects of smoothing parameters on the performance of the BDSM and propose an ad hoc method for identifying appropriate values for those parameters. We also demonstrate the performance of the MCMC approach compared with the LB approach and a penalized partial likelihood method available in software R packages. A gastric cancer trial is utilized to illustrate the application of the BDSM.

Effect of treatment and adherence on ethnic differences in blood pressure control among adults with hypertension.

We evaluated whether hypertension control differs by ethnicity after accounting for patient characteristics, treatment, and adherence to treatment using the third National Health and Nutrition Examination Survey (US population estimate, 42,511,379). Outcome measures were prescribed treatment, treatment adherence, hypertension control (blood pressure [BP]<140/90 mm Hg). Multivariate logistic regression was performed with non-Hispanic whites (NHW) as the comparison group. Non-Hispanic blacks (NHB) were more likely to report medication prescription (odds ratio [OR] 1.6, 95% confidence interval [CI] 1.1-2.5) and being advised to restrict salt (OR 1.5, CI: 1.2-2.0). Among those advised, NHB were more likely to report salt restriction (OR 1.5, CI: 1.1-2.1) and weight-loss attempts (OR 1.7, CI: 1.3-2.3). Among persons advised to follow exercise, alcohol restriction, smoking cessation, tension reduction, or diet modification, NHB (OR 2.2, CI: 1.6-3.0) and Mexican Americans (OR 2.0, CI: 1.1-3.9) were more likely to report adherence. The likelihood of uncontrolled hypertension was higher in NHB (OR 1.4, CI: 1.1-1.7) and Mexican Americans (OR 1.5, CI 1.1-2.0) despite medication adherence. Even after adjustment for treatment and adherence, substantial ethnic differences in hypertension control were found. Initiating treatment, while crucial, is not sufficient and future guidelines should emphasize aggressive treatment escalation to achieve hypertension control.

Thirty-year Survival for Black and White Hypertensive Individuals in the Evans County Heart Study and the Hypertension Detection and Follow-up Program.

The Evans County Heart Study (ECHS), initiated in 1960, was one of the first major studies to document cardiovascular disease (CVD) risks for African Americans and Caucasians with elevated blood pressures. In the early 1970's, the Hypertension Detection and Follow-up Program (HDFP), with a site in Georgia (HDFP-GA) was one of the first major studies to demonstrate that treating hypertension with stepped care (SC), versus referred care (RC), has better short-term outcomes. With this background, study objectives were to evaluate 30-year survival and cardiovascular outcomes of the HDFP-GA and to compare outcomes of these patients with 1619 hypertensive individuals (30-69 years of age) from the ECHS. HDFP-GA patients included 688 individuals (black [n=267]; white [n=421]) randomized to RC (n=341) and SC (n=347). The ECHS was comprised of 733 black and 886 white hypertensives. All-cause mortality and CVD mortality were assessed in the HDFP-GA and compared to the ECHS hypertensives. After 30-years of follow-up, 65.7% of the HDFP-GA cohort had died compared with a similar 65.8% of the ECHS hypertensives. However, CVD mortality rates, while similar for the SC and RC arms, were lower than in the HDFP-GA total study group than the hypertensive participants of ECHS (32.6% vs. 40.3% p<.001). CVD survival rates for both SC and RC HDFP-GA arms were significantly better than population-based hypertensive individuals in the ECHS, with consistent benefits in all four race-sex groups. These results identify the importance of long-term follow-up of individuals in hypertension studies and trials that include CVD outcomes.

Protein and legume intake and prostate cancer mortality in Puerto Rican men.

Prostate cancer is the number 1 cancer killer among Puerto Rican (PR) men. Plant foods have been inversely associated with prostate cancer. Legumes play a significant role in the PR diet; consumption of legumes in PR (14 lb/capita) was double that of the United States (7 lb/capita). We examined dietary protein consumption (from baseline 24-h dietary recalls) and prostate cancer mortality in the PR Heart Health Program, a cohort study of 9,824 men aged 35-79 years at baseline (1964) with follow-up until 2005. Total protein intake in the cohort was 85 g/day, and sources of protein were 30% vegetable, 30% dairy, 31% animal, and 8% seafood protein. Legume intake was 2.3 servings/day (1/4 cup each). Legume intake was not associated with prostate cancer mortality [comparing highest quartile to lowest quartile-odds ratio (OR) 1.40 [95% confidence interval (CI) 0.91-2.18], P trend 0.17]-nor were total protein, animal, seafood, dairy, or vegetable protein intakes. Consuming 1-2 servings of fruit was inversely associated (OR 0.50, 95% CI 0.32-0.77), whereas consuming more than 2 servings of fruit was not associated with prostate cancer mortality. Thus, we find no association between legumes or protein intake and prostate cancer mortality in this longitudinal cohort study of PR men.

Sex differences in the effect of diabetes duration on coronary heart disease mortality.

BACKGROUND: It is not known whether the coronary heart disease (CHD) mortality risk associated with recent (RDM; <10 years) or long-standing diabetes mellitus (LDM; > or =10 years) varies by sex. METHODS: The relationship between diabetes duration and CHD mortality was evaluated among 10 871 adults (aged 35-74 years at baseline) using the 1971-1992 National Health and Nutrition Examination Survey Epidemiologic Follow-up Study. RESULTS: The CHD mortality rates per 1000 person-years in men with no myocardial infarction (MI) or diabetes, MI only, RDM only, LDM only, MI and RDM, and MI and LDM were 5.5 (95% confidence interval, 4.8-6.2), 15.2 (11.6-20.0), 13.2 (7.9-22.1), 11.4 (6.4-20.3), 36.0 (16.7-77.7), and 35.4 (14.0-89.7), respectively. The corresponding rates in women were 2.9 (2.5-3.3), 7.3 (5.0-10.8), 5.2 (3.5-7.7), 10.7 (7.5-15.5), 9.3 (4.3-19.9), and 21.6 (6.1-76.0), respectively. Compared with MI, the multivariate hazard ratios and their 95% confidence intervals (adjusted for age, race, smoking, hypertension, total cholesterol level, and body mass index) for fatal CHD in men with RDM, LDM, MI and RDM, and MI and LDM were 0.7 (0.3-1.3), 0.8 (0.4-1.4), 3.2 (1.4-7.4), and 2.4 (0.8-6.7), respectively. The corresponding ratios in women were 0.9 (0.6-1.3), 1.8 (1.1-3.2), 1.3 (0.5-3.5), and 1.6 (0.2-10.9), respectively. CONCLUSIONS: In men, RDM and LDM were associated with as high a risk for CHD death as MI. In women, although RDM had a CHD mortality risk similar to MI, LDM had an even greater risk. Because women with LDM are at very high risk for CHD mortality, current guidelines may need to be further refined to match intensity of treatment to risk in these women.

Body mass index and mortality: a meta-analysis based on person-level data from twenty-six observational studies.

PURPOSE: For this report, we examined the relationships between the conditions of being overweight and obese and mortality from all causes, heart disease, cardiovascular disease, and cancer. METHODS: We defined the categories of body weight according to level of body mass index, BMI=wt(kg)/ht(m)2, using classifications suggested by the National Institutes of Health and the World Health Organization. These classifications are as follows: "normal weight" is defined as BMI > or = 18.5, but less than 25; "overweight" equals BMI > or = 25, but less than 30; and "obese" individuals have BMIs > or = 30. Our investigation is based on person-level data from 26 observational studies that include both genders, several racial and ethnic groups, and samples from the US and other countries. The database consists of 74 analytic cohorts, arranged according to natural strata including gender, race, and area of residence. It includes 388,622 individuals, with 60,374 deaths during follow-up. We use proportional hazards models to examine the relationships between the BMI categories and mortality, controlling for age and smoking status. We use random-effects models to assess summary relative risks associated with the overweight and obesity conditions across cohorts. RESULTS: The relative risks among the heaviest individuals for overall death, death caused by coronary heart disease (CHD), and death caused by cardiovascular disease (CVD) are 1.22, 1.57, and 1.48, respectively, when compared with the those within the lowest BMI category. The summary relative risk among the heaviest participants for death from cancer is 1.07. CONCLUSIONS: We document once again, excess mortality associated with obesity. Our results do, however, question whether the current classification of individuals as "overweight" is optimal in the sense, since there is little evidence of increased risk of mortality in this group.

Sex differences in risk for coronary heart disease mortality associated with diabetes and established coronary heart disease.

BACKGROUND: The sex-specific independent effect of diabetes mellitus and established coronary heart disease (CHD) on subsequent CHD mortality is not known. METHODS: This is an analysis of pooled data (n = 5243) from the Framingham Heart Study and the Framingham Offspring Study with follow-up of 20 years. At baseline (1971-1975), 134 men and 95 women had diabetes, while 222 men and 129 women had CHD. Risk for CHD death was analyzed by proportional hazards models, adjusting for age, hypertension, serum cholesterol levels, smoking, and body mass index. The comparative effect of established CHD vs diabetes on the risk of CHD mortality was tested by testing the difference in log hazards. RESULTS: The adjusted hazard ratios (HRs) with 95% confidence intervals (CIs) for death from CHD were 2.1 (95% CI, 1.3-3.3) in men with diabetes only, and 4.2 (95% CI, 3.2-5.6) in men with CHD only compared with men without diabetes or CHD. The HR for CHD death was 3.8 (95% CI, 2.2-6.6) in women with diabetes, and 1.9 (95% CI, 1.1-3.4) in women with CHD. The difference between the CHD and the diabetes log hazards was +0.73 (95% CI, 0.72-0.75) in men and -0.65 (95% CI, -0.68 to -0.63) in women. CONCLUSIONS: In men, established CHD signifies a higher risk for CHD mortality than diabetes. This is reversed in women, with diabetes being associated with greater risk for CHD mortality. Current treatment recommendations for women with diabetes may need to be more aggressive to match CHD mortality risk.

The relationship of physical activity and body weight with all-cause mortality: results from the Puerto Rico Heart Health Program.

PURPOSE: To study the relationship of physical activity and obesity with all-cause mortality in Puerto Rican Men. METHODS: The Puerto Rico Heart Health Program collected physical activity and anthropometric measurements in 9,824 men between 1962 and 1965. After excluding those with known coronary heart disease at baseline, and those who died within the first three years of the study we analyzed the data for the relationship between physical activity and overweight status to all-cause mortality in 9,136 men. We stratified our participants by quartiles of physical activity. Participants were classified into four categories of body weight: underweight (BMI < 18.5), healthy weight (BMI =18.5-24.9), overweight (BMI = 25-29.9), and obese (BMI = 30+). RESULTS: After adjusting for age, education, smoking status, hypertension status, hypercholesterolemic status, urban/rural residence, and overweight status, physical activity was independently related to all-cause mortality. All-cause mortality was lower in those in quartile 2 (OR = 0.68, CI = 0.58-0.79) than quartile 1 (reference, sedentary group). Mortality among those in quartile 3 and 4 (0.63, CI = 0.54-0.75; and 0.55, CI = 0.46-0.65, respectively) were also significantly lower than those observed in quartile 1, but not significantly lower than those observed in quartile 2. Furthermore, within every category of body weight, those who were most active had significantly lower odds ratio of all-cause mortality. CONCLUSION: Our findings support the current recommendation that some physical activity is better than none, in protecting against all-cause mortality. The benefits of an active lifestyle are independent of body weight and that overweight and obese Puerto Rican men who are physically active experienced significant reductions in all-cause mortality compared with their sedentary counterparts.

Effect of cerclage on obstetrical outcome in twin gestations with a shortened cervical length.

OBJECTIVE: Our purpose was to determine the impact of cerclage placement on obstetric outcome in twin gestations with a shortened cervical length. STUDY DESIGN: A prospective cohort study of 147 consecutive twin pregnancies (July 1994 to March 2001) who underwent transvaginal ultrasonographic cervical length measurement between 18 and 26 weeks' gestation. Cerclage was offered to women with cervical lengths < or = 25 mm. Patients were segregated into quartiles by cervical length. Regression analysis and chi(2) tests were used to determine the effect of cervical length and cerclage on parameters of prematurity. RESULTS: One hundred twenty-eight twin gestations met inclusion criteria, including 21 (16.4%) who underwent cerclage for a cervical length < or = 25 mm. Decreasing cervical length was significantly associated with a shorter length of gestation, lower combined birth weight, delivery at < or = 34 weeks, preterm premature rupture of fetal membranes, and very low birth weight. None of these outcomes was altered by cerclage placement. CONCLUSION: Midtrimester cerclage does not alter the risks of prematurity associated with a shortened cervical length in twin gestations.

Relation between body mass index and body fat in black population samples from Nigeria, Jamaica, and the United States

Body mass index (BMI) is the most commonly used measure of obesity. Recently, some investigators have advocated direct measurement of adiposity rather than use of the BMI. This study was undertaken to determine the ability of BMI to predict body fat levels in three populations of West Africa heritage living in different environments. A total of 1,054 black men and women were examined in Nigeria, Jamaica, and the United States during 1994 and 1995. A standardized protocol was used to measure height, weight, waist and hip circumferences, and blood pressure at all sites; percentage of body fat was estimated using bioelectrical impedance analysis. Percentage of body fat and BMI were highly correlated within site- and sex-specific groups, and the resulting r2 ranged from 0.61 to 0.85. The relation was quadratic in all groups except Nigerian men, in whom it was linear. The regression coefficients were similar across sites, yet the mean body fat levels differed significantly (p < 0.001) as estimated by the intercept, making intersite comparison difficult. Compared with BMI, percentage of body fat was not a better predictor of blood pressure or waist or hip circumference.(AU)

The prevalence of hypertension in seven populations of West African origin

OBJECTIVE: This study was undertaken to describe the distribution of blood pressures, hypertension prevalence, and associated risk factors among seven populations of West African origin. METHODS: The rates of hypertension in West Africa (Nigeria and Cameroon), the Caribbean (Jamaica, St. Lucia, Barbados), and the United States (metropolitan Chicago, Illinois) were compared on the basis of a highly standardized collaborative protocol. After researchers were given central training in survey methods, population-based samples of 800 to 2500 adults over the age of 25 were examined in seven sites, yielding a total sample of 10014. RESULTS: A consistent gradient of hypertension prevalence was observed, rising from 16 percent in West Africa to 26 percent in the Caribbean and 33 percent in the United States. Mean blood pressures were similar among persons aged 25 to 34, while the increase in hypertension prevalence with age was twice as steep in the United States as in Africa. Environmental factors, most notably obesity and the intake of sodium and potassium, varied consistently with disease prevalence across regions. CONCLUSION: The findings demonstrate the determining role of social conditions in the evolution of hypertension risk in these populations.(AU)

Obesity in the Caribbean

People of African origin who live in the Caribbean share a common genetic heritage but live in socioeconomic environments that diverge widely. A cross-cultural study of males and females from Jamaica, St. Lucia and Barbados investigated the prevalence of hypertension and its environmental determinants. Standardized measurement techniques allowed comparable measurement of weight, height, waist and hip circumferences, and blood pressure. The population values for body mass index (BMI), percent overweight (males BMI > 27.8 kg/m; females BMI > 27.3 kg/m) and percent obese (males BMI > 31.1 kg/m; females BMI > 32.3 kg/m) are presented. Prevalence of hypertension is base on the age-adjusted total population. The gradient in per capita gross national product in Jamaica, St. Lucia and Barbados parallels the gradient in the proportions of populations in those countries who are obese. BMI explained 26 percent of the variance in blood pressure in females and 13 percent in males. Obesity is a significant problem in the Caribbean, as it is in many other developing countries, and it is associated with a high prevalence of hypertension, particularly in women.(AU)

Obesity in peoples of the African diaspora

People of African descent in the Caribbean and the USA originated from the Bight of Benin in West Africa. Although these population share a common genetic heritage, they now live under different socioeconomical conditions. Assuming genetic similarity, a cross-cultural examination of these peoples in West Africa, the Caribbean and the USA may attenuate the effect of genetic factors and allow the assessment of environmental contributions to a biological outcome. We carried out an epidemiological survey to determine the prevalence of hypertension and the contribution of risk factors to the variation in blood pressure of adults in Nigeria, Cameroon, Jamaica, St. Lucia, Barbados and the USA. In urban populations there was a trend toward increasing weight, height, body mass index, and proportions of those overweight and obese going from West Africa to the USA, with the Caribbean being intermediate. The prevalence of hypertension lay on a similar gradient. Given a common genetic susceptibility, urbanization and western acculturation are therefore associated with increasing hypertension and obesity.(AU)

Obesity and hypertension prevalence in populations of African origin

Obesity has been shown to be associated with hypertension in Africa, the Caribbean, and the United States, but there has not previously been an opportunity to compare the magnitude of this relation and estimate the contribution of obesity to hypertension risk across these populations. The International Collaborative Study on Hypertension in Blacks (ICSHIB) used age-stratified sampling and a standardized protocol to measure blood pressure and hypertension risk factors. We analyzed data on 9,102 men and women, aged 25-74 years, from seven sites. We studied hypertension (140/90 mmHg or medication) in relation to body mass index (BMI) and sex-specific BMI cutpoints designating "overweight" and "obesity". The prevalence of these conditions ranged from 6 percent to 63 percent for overweight, from 1 percent to 36 percent for obesity, and from 12 percent to 35 percent for hypertension. Adjusted relative risks were similar in most sites, ranging form 1.3 to 2.3 for both cutpoints. We found that 6-29 percent of hypertension in each population was attributable to overweight and 0-16 percent to obesity. Comparing rural Africa with the United States, 43 percent of the difference in hypertension prevalence for women was attributable to overweight, and 22 percent for men, whereas respective values for obesity were 14 percent and 11 percent. These results indicate that the association between adiposity and hypertension is roughly constant across a range of environments, with little evidence for variation in susceptibility to effects of overweight in these groups.(AU)

Standardization of blood pressure measurement in an international comparative study

In the context of a collaborative study of hypertension in populations of West Africa origin procedures of standardization on the measurement of blood pressure were evaluated. Comparisons of means levels of blood pressure, which in large part determine prevalence rates, are highly sensitive to differences in technique. While rotating a single field team may be the ideal approach to multisite studies, it is not practical in international collaborative research. Appropriate techniques to standardize multiple teams over a long period of time have not been developed, however. In the present study 8981 individuals were examined in eight sites in six countries with the standard mercury sphygmomanometer. An evaluation of the effectiveness of central training, site visits, monitoring of digit preference, and the use of an electronic device for internal standardization is described. In all but one of the sites reliability was high and comparable to the observers at the Coordinating Center. Digit preference for the entire set of measurements was limited (frequency of terminal zero = 23.5 percent for systolic and 28.9 percent for diastolic readings) and could be shown to have virtually no effect on prevalence rates on correlation estimates. Mean differences among observers within a given site and between sites were small (ñ-5 mmHg). While logistically complex, these methods can provide the basis for standardization in international comparative blood pressure surveys.(AU)

Obesity in peoples of the African diaspora

People of African descent in the Caribbean and the USA originated from the Bight of Benin in West Africa. Although these populations share a common genetic heritage, they now live under different socioeconomical conditions. Assuming genetic similarity, a cross-cultural examination of these peoples in West Africa, the Caribbean and the USA may attenuate the effect of genetic factors and allow the assessment of environmental contributions to a biological outcome. We carried out an epidemiological survey to determine the prevalence of hypertension and the contribution of risk factors to the variation in blood pressure. We measured the height, weight, waist and hip circumferences, and blood pressure of adults in Nigeria, Cameroon, Jamaica, St. Lucia, Barbados and the USA. In urban populations there was a trend towards increasing weight, height, body mass index, and proportions of those overweight and obese going from West Africa to the USA, with the Caribbean being intermediate. The prevalence of hypertension lay on a similar gradient. Given a common genetic susceptibility, urbanization and western acculturation are therefore associated with increasing hypertension and obesity.(AU)

Obesity in the Caribbean

People of African origin who lived in the Caribbean share a common genetic heritage but live in socioeconomic environments that diverge widely. A cross-cultural study of males and females from Jamaica, St. Lucia and Barbados investigated the prevalence of hypertension and its environmental determinants. Standardized measurement techniques allowed comparable measurements of weight, height, waist and hip circumferences, and blood pressure. The population values for body mass index (BMI), per cent overweight (males BMI > or = 27.8 kg/m2; females BMI > or 27.3 kg/m2) and per cent obese (males BMI > or = 31.1 kg/m2; females BMI > or = 32.3 kg/m2) are presented. Prevalence of hypertension is based on the age-adjusted total population. The gradient in per capita gross national product in Jamaica, St. Lucia and Barbados parallels the gradient in the proportions of population in those countries who are obese. BMI explained 26 percent of the variance in blood pressure in females and 13 percent in males. Obesity is a significant problem in the Caribbean, as it is in many other developing countries, and it is associated with a high prevalence of hypertension, particularly in women.(AU)