Improved survival with an implanted defibrillator in patients with coronary disease at high risk for ventricular arrhythmia. Multicenter Automatic Defibrillator Implantation Trial Investigators

BACKGROUND

Unsustained ventricular tachycardia in patients with previous myocardial infarction and left ventricular dysfunction is associated with a two-year mortality rate of about 30 percent. We studied whether prophylactic therapy with an implanted cardioverter-defibrillator, as compared with conventional medical therapy, would improve survival in this high-risk group of patients.

METHODS

Over the course of five years, 196 patients in New York Heart Association functional class I, II, or III with prior myocardial infarction; a left ventricular ejection fraction < or = 0.35; a documented episode of asymptomatic unsustained ventricular tachycardia; and inducible, nonsuppressible ventricular tachyarrhythmia on electrophysiologic study were randomly assigned to receive an implanted defibrillator (n = 95) or conventional medical therapy (n=101). We used a two-sided sequential design with death from any cause as the end point.

RESULTS

The base-line characteristics of the two treatment groups were similar. During an average follow-up of 27 months, there were 15 deaths in the defibrillator group (11 from cardiac causes) and 39 deaths in the conventional-therapy group (27 from cardiac causes) (hazard ratio for overall mortality, 0.46; 95 percent confidence interval, 0.26 to 0.82; P=0.009). There was no evidence that amiodarone, beta-blockers, or any other antiarrhythmic therapy had a significant influence on the observed hazard ratio.

CONCLUSIONS

In patients with a prior myocardial infarction who are at high risk for ventricular tachyarrhythmia, prophylactic therapy with an implanted defibrillator leads to improved survival as compared with conventional medical therapy.

Healthy percentage body fat ranges: an approach for developing guidelines based on body mass index

BACKGROUND

Although international interest in classifying subject health status according to adiposity is increasing, no accepted published ranges of percentage body fat currently exist. Empirically identified limits, population percentiles, and z scores have all been suggested as means of setting percentage body fat guidelines, although each has major limitations.

OBJECTIVE

The aim of this study was to examine a potential new approach for developing percentage body fat ranges. The approach taken was to link healthy body mass index (BMI; in kg/m(2)) guidelines established by the National Institutes of Health and the World Health Organization with predicted percentage body fat.

DESIGN

Body fat was measured in subjects from 3 ethnic groups (white, African American, and Asian) who were screened and evaluated at 3 universities [Cambridge (United Kingdom), Columbia (United States), and Jikei (Japan)] with use of reference body-composition methods [4-compartment model (4C) at 2 laboratories and dual-energy X-ray absorptiometry (DXA) at all 3 laboratories]. Percentage body fat prediction equations were developed based on BMI and other independent variables.

RESULTS

A convenient sample of 1626 adults with BMIs < or =35 was evaluated. Independent percentage body fat predictor variables in multiple regression models included 1/BMI, sex, age, and ethnic group (R: values from 0.74 to 0.92 and SEEs from 2.8 to 5.4% fat). The prediction formulas were then used to prepare provisional healthy percentage body fat ranges based on published BMI limits for underweight (<18.5), overweight (> or =25), and obesity (> or =30).

CONCLUSION

This proposed approach and initial findings provide the groundwork and stimulus for establishing international healthy body fat ranges.

What is the best measure of adiposity change in growing children: BMI, BMI %, BMI z-score or BMI centile?

BACKGROUND

Weight control programs for obese children monitor change in body mass index (BMI) adjusted for age. However, change can be measured in several ways: raw (kg/m2) units, percentage, z-scores or centiles. The suitability of the different measures is not known.

AIM

To identify the optimal BMI measure for change, whose short-term variability is most consistent for children across the spectrum of adiposity.

SETTING

An Italian kindergarten.

SUBJECTS

A total of 135 (66 female) children aged 29-68 months at baseline, with BMI measured three times over a 9-month period.

METHODS

Each child's short-term variability in adiposity was summarized by the standard deviation (s.d.) of BMI and BMI % adjusted for age, and BMI z-score and BMI centile. The s.d.'s were then compared in obese and nonobese children, and also correlated with each child's baseline BMI z-score.

RESULTS

The within-child s.d.s of BMI z-score and BMI centile were significantly smaller in obese than nonobese children, while the s.d.s of BMI and BMI % were similar in the two groups. Also, the within-child s.d.s of z-score and centile, and to a lesser extent BMI %, were significantly inversely correlated with baseline z-score, whereas the s.d. of BMI was not. The changes in adiposity over time, as assessed by the four measures, were very highly correlated with each other, particularly for BMI with BMI %.

DISCUSSION

Even though BMI z-score is optimal for assessing adiposity on a single occasion, it is not necessarily the best scale for measuring change in adiposity, as the within-child variability over time depends on the child's level of adiposity. Better alternatives are BMI itself or BMI %. Our results underscore the importance of using a relatively stable method to assess adiposity change when following children at risk of obesity.

Antipsychotic-induced weight gain: a comprehensive research synthesis

OBJECTIVE

The purpose of this study was to estimate and compare the effects of antipsychotics-both the newer ones and the conventional ones-on body weight.

METHOD

A comprehensive literature search identified 81 English- and non-English-language articles that included data on weight change in antipsychotic-treated patients. For each agent, a meta-analysis and random effects metaregression estimated the weight change after 10 weeks of treatment at a standard dose. A comprehensive narrative review was also conducted on all articles that did not yield quantitative information but did yield important qualitative information.

RESULTS

Placebo was associated with a mean weight reduction of 0.74 kg. Among conventional agents, mean weight change ranged from a reduction of 0.39 kg with molindone to an increase of 3.19 kg with thioridazine. Among newer antipsychotic agents, mean increases were as follows: clozapine, 4.45 kg; olanzapine, 4.15 kg; sertindole, 2.92 kg; risperidone, 2.10 kg; and ziprasidone, 0.04 kg. Insufficient data were available to evaluate quetiapine at 10 weeks.

CONCLUSIONS

Both conventional and newer antipsychotics are associated with weight gain. Among the newer agents, clozapine appears to have the greatest potential to induce weight gain, and ziprasidone the least. The differences among newer agents may affect compliance with medication and health risk.

Total-body skeletal muscle mass: development and cross-validation of anthropometric prediction models

BACKGROUND

Skeletal muscle (SM) is a large body compartment of biological importance, but it remains difficult to quantify SM with affordable and practical methods that can be applied in clinical and field settings.

OBJECTIVE

The objective of this study was to develop and cross-validate anthropometric SM mass prediction models in healthy adults.

DESIGN

SM mass, measured by using whole-body multislice magnetic resonance imaging, was set as the dependent variable in prediction models. Independent variables were organized into 2 separate formulas. One formula included mainly limb circumferences and skinfold thicknesses [model 1: height (in m) and skinfold-corrected upperarm, thigh, and calf girths (CAG, CTG, and CCG, respectively; in cm)]. The other formula included mainly body weight (in kg) and height (model 2). The models were developed and cross-validated in nonobese adults [body mass index (in kg/m(2)) < 30].

RESULTS

Two SM (in kg) models for nonobese subjects (n = 244) were developed as follows: SM = Ht x (0.00744 x CAG(2) + 0.00088 x CTG(2) + 0.00441 x CCG(2)) + 2.4 x sex - 0.048 x age + race + 7.8, where R:(2) = 0.91, P: < 0.0001, and SEE = 2.2 kg; sex = 0 for female and 1 for male, race = -2.0 for Asian, 1.1 for African American, and 0 for white and Hispanic, and SM = 0.244 x BW + 7.80 x Ht + 6.6 x sex - 0.098 x age + race - 3.3, where R:(2) = 0.86, P: < 0.0001, and SEE = 2.8 kg; sex = 0 for female and 1 for male, race = -1.2 for Asian, 1.4 for African American, and 0 for white and Hispanic.

CONCLUSION

These 2 anthropometric prediction models, the first developed in vivo by using state-of-the-art body-composition methods, are likely to prove useful in clinical evaluations and field studies of SM mass in nonobese adults.

Weight management using a meal replacement strategy: meta and pooling analysis from six studies

OBJECTIVE

Although used by millions of overweight and obese consumers, there has not been a systematic assessment on the safety and effectiveness of a meal replacement strategy for weight management. The aim of this study was to review, by use of a meta- and pooling analysis, the existing literature on the safety and effectiveness of a partial meal replacement (PMR) plan using one or two vitamin/mineral fortified meal replacements as well as regular foods for long-term weight management.

DESIGN

A PMR plan was defined as a program that prescribes a low calorie (>800<or=1600 kcal/day) diet whereby one or two meals are replaced by commercially available, energy-reduced product(s) that are vitamin and mineral fortified, and includes at least one meal of regular foods. Randomized, controlled PMR interventions of at least 3 months duration, with subjects 18 y of age or older and a BMI>or=25 kg/m(2), were evaluated. Studies with self-reported weight and height were excluded. Searches in Medline, Embase, and the Cochrane Clinical Trials Register from 1960 to January 2001 and from reference lists identified 30 potential studies for analysis. Of these, six met all of the inclusion criteria and used liquid meal replacement products with the associated plan. Overweight and obese subjects were randomized to the PMR plan or a conventional reduced calorie diet (RCD) plan. The prescribed calorie intake was the same for both groups. Authors of the six publications were contacted and asked to supply primary data for analysis. Primary data from the six studies were used for both meta- and pooling analyses.

RESULTS

Subjects prescribed either the PMR or RCD treatment plans lost significant amounts of weight at both the 3-month and 1-year evaluation time points. All methods of analysis indicated a significantly greater weight loss in subjects receiving the PMR plan compared to the RCD group. Depending on the analysis and follow-up duration, the PMR group lost approximately 7-8% body weight and the RCD group lost approximately 3-7% body weight. A random effects meta-analysis estimate indicated a 2.54 kg (P<0.01) and 2.43 kg (P=0.14) greater weight loss in the PMR group for the 3-month and 1-y periods, respectively. A pooling analysis of completers showed a greater weight loss in the PMR group of 2.54 kg (P<0.01) and 2.63 kg (P<0.01) during the same time period. Risk factors of disease associated with excess weight improved with weight loss in both groups at the two time points. The degree of improvement was also dependent on baseline risk factor levels. The dropout rate for PMR and RCD groups was equivalent at 3 months and significantly less in the PMR group at 1 y. No reported adverse events were attributable to either weight loss regimen.

CONCLUSION

This first systematic evaluation of randomized controlled trials utilizing PMR plans for weight management suggests that these types of interventions can safely and effectively produce significant sustainable weight loss and improve weight-related risk factors of disease.

Why are there race/ethnic differences in adult body mass index-adiposity relationships? A quantitative critical review

Body mass index (BMI) is now the most widely used measure of adiposity on a global scale. Nevertheless, intense discussion centers on the appropriateness of BMI as a phenotypic marker of adiposity across populations differing in race and ethnicity. BMI-adiposity relations appear to vary significantly across race/ethnic groups, but a collective critical analysis of these effects establishing their magnitude and underlying body shape/composition basis is lacking. Accordingly, we systematically review the magnitude of these race-ethnic differences across non-Hispanic (NH) white, NH black and Mexican American adults, their anatomic body composition basis and potential biologically linked mechanisms, using both earlier publications and new analyses from the US National Health and Nutrition Examination Survey. Our collective observations provide a new framework for critically evaluating the quantitative relations between BMI and adiposity across groups differing in race and ethnicity; reveal new insights into BMI as a measure of adiposity across the adult age-span; identify knowledge gaps that can form the basis of future research and create a quantitative foundation for developing BMI-related public health recommendations.

The distribution of body mass index among individuals with and without schizophrenia

OBJECTIVE

The objective of this study was to estimate and compare the distributions of body mass index (BMI: kg/m2) among individuals with and without schizophrenia, and, thereby, place the weight gain-inducing effects of antipsychotic drugs into context.

METHOD

Data sources were (1) the mental health supplement of the 1989 National Health Interview Survey (NHIS; N = 80,130 nonschizophrenic and 150 self-reported schizophrenic individuals), (2) baseline BMI data from a drug trial of the anti-psychotic ziprasidone supplied by Pfizer Inc (420 noninstitutionalized individuals with chronic psychotic disorders [DSM-IV schizophrenia or schizoaffective disorder]) and (3) data from the National Health and Nutrition Examination Survey III (NHANES III; N = 17,689 nonschizophrenic individuals) to act as a control group for the ziprasidone trial data.

RESULTS

After age-adjusting BMI in each data set, the NHIS data revealed that men with schizophrenia have mean BMIs similar to those of men without schizophrenia (26.14 vs. 25.63, respectively). In contrast, women with schizophrenia in the NHIS data set had a significantly (p<.001) higher mean BMI than did women without schizophrenia (27.36 vs. 24.50, respectively). Moreover, each decile was higher for women with schizophrenia than for women without schizophrenia. Analysis of the ziprasidone and NHANES III data sets revealed that, on average, men with schizophrenia have mean BMIs comparable to those of men without schizophrenia (26.79 vs. 26.52, respectively). In these 2 data sets, women with schizophrenia also had a mean BMI similar to those of women without schizophrenia (27.29 vs. 27.39, respectively).

CONCLUSION

Although there may be a small subpopulation of schizophrenic individuals who are underweight, individuals with schizophrenia were, on the whole, as obese as or more obese than individuals without schizophrenia, suggesting that weight gain induced by antipsychotic agents is an important concern for many individuals.

Depressive mood and obesity in US adults: comparison and moderation by sex, age, and race

OBJECTIVE

Sustained depressive mood is a gateway symptom for a major depressive disorder. This paper investigated whether the association between depressive mood and obesity differs as function of sex, age, and race in US adults after controlling for socio-economic variables of martial status, employment status, income level and education level.

METHODS

A total of 44,800 nationally representative respondents from the 2001 Behavioral Risk Factor Surveillance Survey were studied. Respondents were classified as having experienced a depressive mood if they felt sad, blue, or depressed at least for 1 week in the previous month. The depressive mood was operationalized in terms of duration and sustenance, both defined based on number of days with depressive mood: 7+ and 14+ days. Age groups were classified as young (18-64 years) and old (65+ years). Obesity status was classified as: not overweight/obese (BMI<25); overweight (25<or=BMI<30); obese (BMI>or=30).

RESULTS

Prevalence of prior-month depressive mood was 14.3 and 7.8% for 7+ and 14+ days, respectively. Controlling for race and socio-economic variables, both young overweight and obese women were significantly more likely to have experienced depressive mood than nonoverweight/nonobese women. Young overweight, but not obese, men were significantly more likely to have experienced depressive mood than nonoverweight/nonobese men. Young obese women were also significantly more likely to have a sustained depressive mood than nonoverweight/nonobese women. For old respondents, depressive mood and its sustenance were not associated with obesity in either sex.

DISCUSSION

The relationship between the depressive mood and obesity is dependent upon gender, age, and race. Young obese women, Hispanics in particular, are much more prone to depressive mood than nonobese women. Future studies testing associations between depression and obesity should be sensitive to the influence of these demographic and socio-economic variables.

Weight loss increases and fat loss decreases all-cause mortality rate: results from two independent cohort studies

OBJECTIVE

In epidemiological studies, weight loss is usually associated with increased mortality rate. Contrarily, among obese people, weight loss reduces other risk factors for disease and death. We hypothesised that this paradox could exist because weight is used as an implicit adiposity index. No study has considered the independent effects of weight loss and fat loss on mortality rate. We studied mortality rate as a function of weight loss and fat loss.

DESIGN

Analysis of 'time to death' in two prospective population-based cohort studies, the Tecumseh Community Health Study (1890 subjects; 321 deaths within 16y of follow-up) and the Framingham Heart Study (2731 subjects; 507 deaths within 8y of follow-up), in which weight and fat (via skinfolds) loss were assessable.

RESULTS

In both studies, regardless of the statistical approach, weight loss was associated with an increased, and fat loss with a decreased, mortality rate (P < 0.05). Each standard deviation (s.d.) of weight loss (4.6 kg in Tecumseh, 6.7 kg in Framingham) was estimated to increase the hazard rate by 29% (95% confidence interval CI), (14%, 47%, respectively) and 39% (95% CI, 25%, 54% respectively), in the two samples. Contrarily, each s.d. of fat loss (10.0 mm in Tecumseh, 4.8 mm in Framingham) was estimated to reduce the hazard rate 15% (95% CI, 4%, 25%) and 17% (95% CI, 8%, 25%) in Tecumseh and Framingham, respectively. Generalisability of these results to severely (that is, body mass index BMI) > or = 34) obese individuals is unclear.

CONCLUSIONS

Among individuals that are not severely obese, weight loss is associated with increased mortality rate and fat loss with decreased mortality rate.

Estimating the consequences of anti-psychotic induced weight gain on health and mortality rate

Many anti-psychotic medications produce marked weight gain. In this study, we estimate the expected impact of degrees of antipsychotic-induced weight gain on selected mortality rate and incidence rates of impaired glucose tolerance (IGT) and hypertension (HTN) among US adults. Using raw data from 5209 respondents from the Framingham Heart Study's public use data set and national statistics on population demographics, we estimated the expected effect of weight gain on number of deaths and incident cases of IGT and HTN for a 10-year period commencing in 1999. Results indicated that the estimated deleterious effects of weight gain were greater for people with higher BMIs at baseline, for greater degrees of weight gain, for men than women, and for older than younger persons. Because there is a 'U-shaped' relation between BMI and mortality rate, small to moderate weight gains among people with baseline BMIs less than 23 were predicted to decrease mortality rates, whereas weight gains among people with baseline BMIs above that level were expected to increase mortality rates. However, the relations of IGT and HTN with BMI are monotonically increasing. Thus, the anticipated effect of weight gain on IGT and HTN is deleterious regardless of baseline BMI. Because it is unclear whether the beneficial effects of the atypical agents on, for example, reducing suicide mortality, outweigh the putative increase in mortality due to weight gain, we estimate the beneficial effects due to decreased death from suicide with the potential deleterious effects due to a 10-kg weight gain. We found that 492 suicide deaths per 100,000 schizophrenic patients would be prevented over 10 years with the use of clozapine compared to 416 additional deaths due to antipsychotic induced weight gain. Although this estimate is rather crude and should be seen only as offering a sense of the likely situation, results suggest that the lives saved via clozapine may essentially be offset by the deaths due to weight gain. As we discuss, it is not possible to provide definitive estimates of the effect of antipsychotic-induced weight gain on health and mortality, but our findings suggest that the magnitude of weight gains induced by many antipsychotic agents is likely to have important deleterious effects on mortality and health.

Hypothesis concerning the U-shaped relation between body mass index and mortality

Numerous studies have documented a U- or J-shaped association between body mass index (BMI) (kg/m2) and mortality, such that increased mortality rate is associated with relatively low and high BMI values. It has been argued elsewhere that the elevated mortality rate observed at lower BMI values actually results from the effects of unmeasured confounding variables, in particular smoking status and preexisting disease. In this paper, the authors present an additional explanation for the phenomenon, i.e., nonspecific measurement. They propose that differential health consequences of fat mass and fat-free mass can be masked by the use of BMI when studied in relation to mortality. To illustrate this point, they use body composition data from 1,137 healthy adults and specify a hypothetical underlying BMI-mortality model in which the logit of death increased linearly with fat mass and decreased linearly with fat-free mass, and % fat increased monotonically with BMI. The results indicate that, even under these specifications, the authors can recover a U-shaped association between BMI and mortality. Consistent with previous suggestions in the literature, future epidemiologic studies that examine the association between adiposity and mortality should prioritize the use of body composition measures.

Differential associations of body mass index and adiposity with all-cause mortality among men in the first and second National Health and Nutrition Examination Surveys (NHANES I and NHANES II) follow-up studies

OBJECTIVE

The frequently observed U-shaped relationship between body mass index (BMI; kg/m(2)) and mortality rate may be due to the opposing effects of fat mass (FM) and fat-free mass (FFM) components of BMI on mortality rate. The purpose is to test the hypothesis stated above.

DESIGN

Longitudinal prospective cohort studies. The mortality follow-up of the first and second National Health and Nutrition Examination Surveys (NHANES I and NHANES II).

SUBJECTS

A total of 10 169 male subjects aged 25-75 who participated in NHANES I and II were selected for analyses. Follow-up continued until 1992. The mean follow-up time was 14.6 y for NHANES I and 12.9 y for NHANES II. Ninety-eight percent of the participants were successfully followed representing a total of 3722 deaths.

MEASUREMENTS

Subscapular and triceps skinfolds thickness were used as FM indicators, whereas upper arm circumference was used as a FFM indicator. The Cox proportional hazards model tested the relationships of BMI, FM and FFM with all-cause mortality adjusting for age, smoking status, race and education levels.

RESULTS

BMI had a U-shaped relationship with mortality, with a nadir of approximately 27 kg/m(2). However, when indicators of FM and FFM were added to the model, the relationship between BMI and mortality became more nearly monotonic increasing. Moreover, the relationship between FM indicator and mortality was monotonic increasing and the relationship between FFM indicator and mortality was monotonic decreasing.

CONCLUSION

These results support the hypothesis that the apparently deleterious effects of marked thinness may be due to low FFM and that, over the observed range of the data, marked leanness (as opposed to thinness) has beneficial effects.

Body mass index and all-cause mortality among people age 70 and over: the Longitudinal Study of Aging

OBJECTIVES

To assess the relationship between body mass index (BMI; kg/m2) and mortality in a large nationally representative sample of US adults over age 70 years.

DESIGN

Prospective longitudinal cohort study, the Longitudinal Study of Aging (LSOA). Subjects were all those 7260 black and white people (2769 men, 4491 women) initially interviewed in 1984 for whom height and weight were available. These subjects were followed through to 1990.

MEASUREMENTS

Measurements included self-reported height and weight, date of death if subjects died, sex, age, race, measures of socio-economic status, number of living first degree relatives, and responses to questions asking whether the subject had retired due to poor health, had difficulty eating, worried about their health, and felt their health was worse than during the prior year. Smoking status was not assessed.

RESULTS

When analyzed via Cox proportional hazard regression, the relationship between BMI and mortality, represented by means of hazard ratio, was clearly U-shaped for both men and women. The base of the curves was fairly wide suggesting that a broad range of BMIs are well tolerated by older adults. The minimum mortality (estimated from the fitted proportional hazard models) occurred at a BMI of approximately 31.7 for women and 28.8 for men. The results were essentially unchanged, if analyses were weighted, if various disease states were controlled for, and if apparently unhealthy subjects were excluded.

CONCLUSIONS

The finding of the relatively high BMI (27-30 for men, 30-35 for women) associated with minimum hazard in persons older than seventy years supports some previously documented findings and opposes others and, if confirmed in future research, has implications for public health and clinical recommendations.

Effects of contingent television on physical activity and television viewing in obese children

OBJECTIVE

Elevated television (TV) viewing and physical inactivity promote obesity in children. Thus, changes in physical activity and sedentary behavior seem critical to treating childhood obesity. PRESENT STUDY: Using a randomized, 2-arm design, this pilot study tested the effects of contingent TV on physical activity and TV viewing in 10 obese children. TV viewing was contingent on pedaling a stationary cycle ergometer for experimental participants but was not contingent on pedaling for control participants. The study was conducted over 12 weeks, including a 2-week baseline period.

RESULTS

Multivariate analyses indicated that the intervention significantly increased pedaling and reduced TV-viewing time. During the treatment phase, the experimental group pedaled 64.4 minutes per week on average, compared with 8.3 minutes by controls. The experimental group watched 1.6 hours of TV per week on average, compared with 21.0 hours per week on average by controls during this phase. Secondary analyses indicated that the experimental group showed significantly greater reductions in total body fat and percent leg fat. Total pedaling time during intervention correlated with greater reductions in percent body fat (r = -0.68).

CONCLUSIONS

Contingencies in the home environment can be arranged to modify physical activity and TV viewing and may have a role in treating childhood obesity. Contingent TV may be one method to help achieve this goal.

A meta-analytic investigation of linkage and association of common leptin receptor (LEPR) polymorphisms with body mass index and waist circumference

METHODS

We analyzed data pooled from nine studies on the human leptin receptor (LEPR) gene for the association of three alleles (K109R, Q223R and K656N) of LEPR with body mass index (BMI; kg/m(2)) and waist circumference (WC). A total of 3263 related and unrelated subjects from diverse ethnic backgrounds including African-American, Caucasian, Danish, Finnish, French Canadian and Nigerian were studied. We tested effects of individual alleles, joint effects of alleles at multiple loci, epistatic effects among alleles at different loci, effect modification by age, sex, diabetes and ethnicity, and pleiotropic genotype effects on BMI and WC.

RESULTS

We found that none of the effects were significant at the 0.05 level. Heterogeneity tests showed that the variations of the non-significant effects are within the range of sampling variation.

CONCLUSIONS

We conclude that, although certain genotypic effects could be population-specific, there was no statistically compelling evidence that any of the three LEPR alleles is associated with BMI or WC in the overall population.

Sibling-based tests of linkage and association for quantitative traits

The transmission/disequilibrium test (TDT) developed by Spielman et al. can be a powerful family-based test of linkage and, in some cases, a test of association as well as linkage. It has recently been extended in several ways; these include allowance for implementation with quantitative traits, allowance for multiple alleles, and, in the case of dichotomous traits, allowance for testing in the absence of parental data. In this article, these three extensions are combined, and two procedures are developed that offer valid joint tests of linkage and (in the case of certain sibling configurations) association with quantitative traits, with use of data from siblings only, and that can accommodate biallelic or multiallelic loci. The first procedure uses a mixed-effects (i.e., random and fixed effects) analysis of variance in which sibship is the random factor, marker genotype is the fixed factor, and the continuous phenotype is the dependent variable. Covariates can easily be accommodated, and the procedure can be implemented in commonly available statistical software. The second procedure is a permutation-based procedure. Selected power studies are conducted to illustrate the relative power of each test under a variety of circumstances.

Meta-analysis of the association of the Trp64Arg polymorphism in the beta3 adrenergic receptor with body mass index

OBJECTIVE

As a result of efforts to isolate obesity-promoting genes, the Trp64Arg polymorphism in the beta3 adrenergic receptor locus, has been studied by many investigators. Results of the studies have varied in statistical significance and magnitude of the association of the polymorphism with body mass index (BMI: kg/m2). This has led to controversy about whether this polymorphism is associated with meaningful changes in BMI. To clarify the possible association, we conducted a meta-analysis.

DESIGN

Meta-analytic study.

MEASUREMENTS

For each genotype of the beta3 adrenergic receptor (Trp/Trp; Trp/Arg; Arg/Arg), we extracted the number of subjects, mean and standard deviation of BMI from 23 studies, including 36 different subgroups with a total of 7399 subjects. Other indices and obesity-related variables were not considered.

RESULTS

No significant association of the Trp64Arg polymorphism with BMI was found. The weighted mean BMI difference between Trp/Trp homozygotes and Trp/Arg heterozygotes was 0.19 (s.e. = 0.11; P = 0.07). In addition, the distribution of effect sizes was not significantly heterogeneous (chi2=38.68; df 35; P = 0.31) suggesting that the variation of the effect sizes across the subgroups is not significant. A further weighted regression analysis, utilizing all three genotypes and adjusting for the random subgroup effect, also showed the effect of the polymorphism on BMI is not significant (F = 1.72, df = (2,54), P = 0.19).

CONCLUSION

Based on existing data, the Trp64Arg polymorphism does not appear to be significantly associated with BMI. Moreover, we found no evidence for effect heterogeneity, suggesting that the effect of the polymorphism is not moderated by ethnicity or diabetic status.

Body weight and cancer screening among women

Obesity increases cancer risk, yet small-scale surveys indicate that obese women delay or avoid cancer screening even more so than do nonobese women. We sought to estimate the association between body mass index (BMI) (kg/m(2)) and delayed cancer screening among adult women in a population-based survey. Subjects were women classified by BMI as underweight (<18.5), desirable weight (18.5-24.9), overweight (25-29.9), obese class I (30-34.9), obese class II (35-39.9), and obese class III (> or =40). Outcome measures were intervals (0 for < or =2 years versus 1 for >2 years) since most recent screening for Papanicolaou (Pap) smear, mammography, and clinical breast examination (CBE). Adjusting for age, race, smoking, and health insurance, we observed J-shaped associations between BMI and screening. Compared with desirable weight women, underweight women (odds ratios [OR] = 1.21, 95% confidence interval [95% CI] 1.09-1.34), overweight women (OR = 1.13, 95% CI 1.07-1.18), and obese women (OR range 1.22-1.69) were significantly more likely to delay Pap smear testing for >2 years. Underweight (OR = 1.32, 95% CI 1.13-1.54), obesity class I (OR = 1.12, 95% CI 1.02-1.23), and obesity class III women (OR = 1.32, 95% CI 1.10-1.54) were more likely to delay mammography, and overweight (OR = 1.10, 95% CI 1.01-1.19), obesity class I (OR = 1.18, 95% CI 1.08-1.30), and obesity class III women (OR = 1.47, 95% CI 1.23-1.75) were more likely to delay CBE. White women were more likely to delay CBE as a function of BMI than were non-white women. Weight may be an important correlate of cancer screening behavior, particularly for white women.

Meta-analysis of the effect of excluding early deaths on the estimated relationship between body mass index and mortality

OBJECTIVES

Prospective cohort studies typically observe U- or J-shaped relationships between body mass index (BMI) (kg/m2) and mortality. However, some studies suggest that the elevated mortality at lower BMIs is due to confounding by pre-existing occult disease and recommend eliminating subjects who die during the first several (k) years of follow-up. This meta-analysis tests the effects of such early death exclusion on the BMI-mortality association.

RESEARCH METHODS AND PROCEDURES

Studies identified from MEDLINE, review articles, ancestry analyses, and the "invisible college."

INCLUDED STUDIES

1) measured relative body weight at baseline; 2) included at least 1000 subjects; 3) reported results with and without early-death exclusion, or relevant data; and 4) did not study exclusively diseased populations. Blank tables were mailed to 131 investigators covering 59 databases. Completed tables (n = 16 databases), electronic raw data (n = 7 databases), and original articles (n = 6 databases) provided final data. Meta-analytic regressions compared the BMI-mortality association with and without early death exclusion. The sample included 29 studies and 1,954,345 subjects.

RESULTS

The effect of eliminating early deaths was statistically significant but minuscule in magnitude. Implementation of early death exclusion was estimated to shift the BMI associated with minimum mortality only 0.4 units for men and 0.6 units for women at age 50. Even at a BMI 16, the estimated relative risk (compared to BMI 25) decreased only 0.008 units for men and 0.076 units for women at age 50.

DISCUSSION

Results indicate that either pre-existing disease does not confound the BMI-mortality association or eliminating early deaths is inefficient for reducing that confounding.

Lower limb skeletal muscle mass: development of dual-energy X-ray absorptiometry prediction model

Although magnetic resonance imaging (MRI) can accurately measure lower limb skeletal muscle (SM) mass, this method is complex and costly. A potential practical alternative is to estimate lower limb SM with dual-energy X-ray absorptiometry (DXA). The aim of the present study was to develop and validate DXA-SM prediction equations. Identical landmarks (i.e., inferior border of the ischial tuberosity) were selected for separating lower limb from trunk. Lower limb SM was measured by MRI, and lower limb fat-free soft tissue was measured by DXA. A total of 207 adults (104 men and 103 women) were evaluated [age 43 +/- 16 (SD) yr, body mass index (BMI) 24.6 +/- 3.7 kg/m(2)]. Strong correlations were observed between lower limb SM and lower limb fat-free soft tissue (R(2) = 0.89, P < 0.001); age and BMI were small but significant SM predictor variables. In the cross-validation sample, the differences between MRI-measured and DXA-predicted SM mass were small (-0.006 +/- 1.07 and -0.016 +/- 1.05 kg) for two different proposed prediction equations, one with fat-free soft tissue and the other with added age and BMI as predictor variables. DXA-measured lower limb fat-free soft tissue, along with other easily acquired measures, can be used to reliably predict lower limb skeletal muscle mass.

Risk factors for mortality among MDR- and XDR-TB patients in a high HIV prevalence setting

SETTING

Recent studies suggest that the prevalence of drug-resistant tuberculosis (TB) in sub-Saharan Africa may be rising. This is of concern, as human immunodeficiency virus (HIV) co-infection in multidrug-resistant (MDR) and extensively drug-resistant (XDR) TB has been associated with exceedingly high mortality rates.

OBJECTIVE

To identify risk factors associated with mortality in MDR- and XDR-TB patients co-infected with HIV in South Africa.

DESIGN

Case-control study of patients who died of all causes within 2 years of diagnosis with MDR- or XDR-TB.

RESULTS

Among 123 MDR-TB patients, 78 (63%) died following diagnosis. CD4 count ≤ 50 (HR 4.64, P = 0.01) and 51-200 cells/mm(3) (HR 4.17, P = 0.008) were the strongest independent risk factors for mortality. Among 139 XDR-TB patients, 111 (80%) died. CD4 count ≤ 50 cells/mm(3) (HR 4.46, P = 0.01) and resistance to all six drugs tested (HR 2.54, P = 0.04) were the principal risk factors. Use of antiretroviral therapy (ART) was protective (HR 0.34, P = 0.009).

CONCLUSIONS

Mortality due to MDR- and XDR-TB was associated with greater degree of immunosuppression and drug resistance. Efforts to reduce mortality must focus on preventing the amplification of resistance by strengthening TB treatment programs, as well as reducing the pool of immunosuppressed HIV-infected patients through aggressive HIV testing and ART initiation.

Evidence for independent genetic influences on fat mass and body mass index in a pediatric twin sample

OBJECTIVE

Insight into genetic and environmental influences on fat mass, independent of body mass index (BMI; kg/m2), is expected to enhance methods for treating pediatric obesity. However, few studies have estimated the heritability of fat mass in pediatric samples, and those conducted have relied primarily on BMI measurements. PRESENT STUDY: Using bioimpedance analysis, the present study tested a series of hypotheses predicting significant genetic and environmental influences on percent body fat (PBF) above and beyond BMI. Subjects were 66 pairs of twins, including 41 monozygotic and 25 dizygotic pairs, from 3 to 17 years of age. Structural equation modeling tested hypotheses, adjusting for demographic variables.

RESULTS

Analyses indicated significant genetic influences on PBF, with genes estimated to account for 75% to 80% of the phenotypic variation. The remaining variation was attributable to nonshared environmental influences. Multivariate analyses revealed sizable genetic correlations and environmental correlations between BMI and PBF (rg =.74 and re =.67, respectively), suggesting that some genes and environmental experiences influence both phenotypes. However, analyses confirmed genetic and environmental influences on PBF above and beyond BMI. For example, 62.5% of the total genetic variation in PBF was attributable to genes that influenced PBF but not BMI.

CONCLUSION

There seems to be a substantial genetic contribution to fat mass distinct from BMI in a sample of children and adolescents. Studies testing putative genetic or environmental determinants of pediatric obesity might be strengthened further by including research-based body composition methods.

Muscularity in adult humans: proportion of adipose tissue-free body mass as skeletal muscle

Muscularity, or the proportion of adipose tissue-free body mass (ATFM) as skeletal muscle (SM), provides valuable body composition information, especially for age-related SM loss (i.e., sarcopenia). Limited data from elderly cadavers suggest a relatively constant SM/ATFM ratio, 0.540 +/- 0.046 for men (mean +/- SD, n = 6) and 0.489 +/- 0.049 for women (n = 7). The aim of the present study was to examine the magnitude and constancy of the SM/ATFM ratio in healthy adults. Whole-body SM and ATFM were measured using multi-scan magnetic resonance imaging. The SM/ATFM ratio was 0.528 +/- 0.036 for men (n = 139) and 0.473 +/- 0.037 for women (n = 165). Multiple regression analysis indicated that the SM/ATFM ratio was significantly influenced by sex, age, body weight, and race. The four factors explained 50% of the observed between individual variation in the SM/ATFM ratio. After adjusting for age, body weight, and race, men had a larger SM/ATFM ratio than women. Both older men and women had a lower SM/ATFM ratio than younger subjects, although the relative reduction was greater in men. After adjustment for sex, age, and body weight, there were no significant differences in the SM/ATFM ratios between Asian, Caucasian, and Hispanic subjects. In contrast, African-American subjects had a significantly greater SM/ATFM ratio than subjects in the other three groups. In addition, the SM/ATFM ratio was significantly lower in AIDS patients than corresponding values in healthy subjects.

Relative influences of sex, race, environment, and HIV infection on body composition in adults

BACKGROUND

The factors that control body composition in disease are uncertain.

OBJECTIVE

We planned to compare the relative influences of HIV infection, sex, race, and environment on body composition.

METHODS

We analyzed results of body composition studies performed by bioelectrical impedance analysis in 1415 adults from 2 cohorts: white and African American men and women from the United States, and African men and women (279 HIV-infected and 1136 control). The effects of sex and HIV infection on weight, body cell mass, and fat-free mass were analyzed by using both unadjusted and age-, weight-, and height-adjusted data.

RESULTS

Control men weighed more and had more body cell mass and fat-free mass than did control women, although control women had more fat. The strongest correlates with body composition were height and weight, followed by sex. HIV infection, age, environment, and race. Control men and women weighed more and had more body cell mass, fat-free mass, and fat than did HIV-infected men. However, differences in body composition between HIV-infected and control groups were strongly influenced by sex. Of the differences in weight between HIV-infected and uninfected subjects, fat-free mass accounted for 51% in men but only 18% in women, in whom the remainder was fat. Sex effects were similar in African and American groups.

CONCLUSIONS

Sex has a marked effect on the changes in body composition during HIV infection, with women losing disproportionately more fat than men. Sex-related differences in body composition were narrower in the HIV-infected groups. Race and environment had smaller effects than sex and HIV infection.