PET-CT has low specificity for mediastinal staging of non-small-cell lung cancer in an endemic area for tuberculosis: a diagnostic test study (LACOG 0114).

BACKGROUND: The present study aims to assess the performance of 18F-FDG PET-CT on mediastinal staging of non-small cell lung cancer (NSCLC) in a location with endemic granulomatous infectious disease. METHODS: Diagnostic test study including patients aged 18 years or older with operable stage I-III NSCLC and indication for a mediastinal lymph node biopsy. All patients underwent a 18F-FDG PET-scan before invasive mediastinal staging, either through mediastinoscopy or thoracotomy, which was considered the gold-standard. Surgeons and pathologists were blinded for scan results. Primary endpoint was to evaluate sensitivity, specificity and positive and negative predictive values of PET-CT with images acquired in the 1st hour of the exam protocol, using predefined cutoffs of maximal SUV, on per-patient basis. RESULTS: Overall, 85 patients with operable NSCLC underwent PET-CT scan followed by invasive mediastinal staging. Mean age was 65 years, 49 patients were male and 68 were white. One patient presented with active tuberculosis and none had HIV infection. Using any SUV_max > 0 as qualitative criteria for positivity, sensitivity and specificity were 0.87 and 0.45, respectively. Nevertheless, even when the highest SUV cut-off was used (SUV_max ≥5), specificity remained low (0.79), with an estimated positive predictive value of 54%. CONCLUSIONS: Our findings are in line with the most recent publications and guidelines, which recommend that PET-CT must not be solely used as a tool to mediastinal staging, even in a region with high burden of tuberculosis. TRIAL REGISTRATION: The LACOG 0114 study was registered at ClinicalTrials.gov , before study initiation, under identifier NCT02664792.

Body mass index at 11 years and bone mass at age 18: path analysis within the 1993 Pelotas (Brazil) birth cohort study.

BACKGROUND: We investigated whether Body Mass Index (BMI) at 11 years old has a direct effect on bone mass at age 18 operating through alterations to bone growth and development, or whether the association is mediated by concurrent BMI, fat mass (FM), and fat free mass (FFM). METHODS: Path analysis was used to explore the association between BMI at age 11 and whole-body bone mineral content (BMC) and bone mineral density (BMD) assessed by dual-energy x-ray absorptiometry (DXA) at age 18 in a prospective birth cohort study comprising 3,307 adolescents; we also evaluated the degree to which this association was mediated by BMI, FM (kg) and FFM (kg) assessed by plethysmography (BOD POD) at age 18. RESULTS: We found a positive association between BMI at age 11 and BMC (males [ß = 179.7 g, 95% CI 161.4; 198.0]; females [ß = 179.9 g, 95% CI 165.3; 194.6]) and BMD (males [ß = 0.030 g/cm2, 95% CI 0.024; 0.035]; females [ß = 0.029 g/cm2, 95% CI 0.025; 0.033]) at age 18. This association was largely mediated by BMI and FFM at age 18 in both female and male adolescents. FM at age 18 was not an important mediator. CONCLUSIONS: Concurrent BMI and FFM were the main mediators of the association between BMC/BMD in late adolescence and BMI in early adolescence.

Inequalities in Pap smear screening for cervical cancer in Brazil.

OBJECTIVE: To examine the risk factors associated with never being screened for cervical cancer (CC) in Brazil. METHODS: Using the National Household Sample Survey 2008 (PNAD), we analyzed data from 102,108 Brazilian women ages 25-64years. The patients were analyzed as having been or never having been screened with a Pap smear (Yes/No). Age-adjusted prevalence of never-screening was analyzed using a Chi-squared test. Crude and adjusted models using Poisson regression were performed. RESULTS: The prevalence of never-screened women for CC was 12.9%, 11.5% and 22.2% in Brazil in general, urban and rural areas, respectively. The Brazilian region with the highest prevalence of never-screening was the North (17.4%, 14.7% and 27.3% in general, urban and rural areas, respectively). The factors associated with a higher risk for never being screened were the following: poverty, younger age, lower educational level, non-white skin color, a greater number of children, no supplemental health insurance and not having visited a doctor in the past 12months. CONCLUSION: Socioeconomic and demographic conditions lead to inequalities in access to Pap smear screening in Brazil. Public health policy addressing these risk groups is necessary.

Physical activity during life course and bone mass: a systematic review of methods and findings from cohort studies with young adults.

BACKGROUND: The purpose of this paper was to review the literature of the cohort studies which evaluated the association between physical activity during the life course and bone mineral content or density in young adults. METHODS: Prospective cohort studies with bone mineral density or content measured in the whole body, lumbar spine and femoral neck by dual energy x-ray absorptiometry as outcome and physical activity as exposure were searched. Two independent reviewers selected studies retrieved from electronic databases (Medline, Lilacs, Web of Science and Scielo) and reviewed references of all selected full text articles. Downs & Black criterion was used in the quality assessment of these studies. RESULTS: Nineteen manuscripts met inclusion criteria. Lumbar spine was the skeletal site most studied (n = 15). Different questionnaires were used for physical activity evaluation. Peak strain score was also used to evaluate physical activity in 5 manuscripts. Lack of statistical power calculation was the main problem found in the quality assessment. Positive associations between physical activity and bone mass were found more in males than in females; in weight bearing anatomical sites (lumbar spine and femoral neck) than in total body and when physical activity measurements were done from adolescence to adulthood - than when evaluated in only one period. Physical activity during growth period was associated with greater bone mass in males. It was not possible to conduct pooled analyses due to the heterogeneity of the studies, considering mainly the different instruments used for physical activity measurements. CONCLUSIONS: Physical activity seems to be important for bone mass in all periods of life, but especially the growth period should be taking into account due to its important direct effect on bone mass and its influence in physical activity practice in later life. Low participation in peak strain activities may also explain the lower number of associations found in females.

Socioeconomic trajectory from birth to adolescence and lung function: prospective birth cohort study.

BACKGROUND: Socioeconomic status (SES) has been shown to be an important contributor to lung function. The aim of this study was to evaluate the association between lung function in adolescence and (a) SES at birth; (b) SES in adolescence; (c) SES trajectory from birth to adolescence ('never poor', 'non poor-poor', 'poor-non poor' and 'always poor'). Additionally, we investigate the role of adolescent and parental variables at mediating these associations. METHODS: Prospective birth cohort study in Pelotas, Brazil, including 4,005 adolescents (mean age: 14.7 years) followed up from birth. Lung function was measured by spirometry. Outcome variables were forced expiratory volume in one second in liters (FEV1) and forced vital capacity also in liters (FVC). RESULTS: Mean FEV1 was 3.46 L (95%CI 3.43-3.49) among boys and 2.93 L (95%CI 2.91-2.95) among girls. Mean FVC was 4.00 L (95%CI 3.97; 4.04) among boys and 3.30 L (95%CI 3.27; 3.32) among girls. SES at birth, in adolescence and its trajectory from birth to adolescence were inversely associated with lung function in both adolescent boys and girls. After adjustment for mediating variables, coefficients were largely reduced, particularly among boys, and the main predictor of change in coefficients was the inclusion of height in the models. CONCLUSION: Low income adolescents from Brazil present impaired lung function as compared to the better off, and this is largely explained by height.

Prevalence of symptoms of COVID-19 in the state of Rio Grande do Sul: results of a population-based study with 18,000 participants.

OBJECTIVE: To evaluate the prevalence of reports of symptoms of COVID-19 among individuals with and without antibodies and identify those with greater capability to predict the presence of antibodies against SARS-CoV-2. METHODS: The study uses data collected in phases 5 to 8 of Epicovid-19-RS. The presence of antibodies against SARS-CoV-2 was evaluated by a rapid test. The occurrence of cough, fever, palpitations, sore throat, difficulty breathing, changes in taste and smell, vomiting, diarrhea, body pain, shaking, and headache since March 2020 was also evaluated. Then, the capability to predict the evaluated symptoms concerning the presence of antibodies was calculated. RESULTS: A total of 18,000 individuals were interviewed and 181 had antibodies against COVID-19 in phases 5 to 8. The proportion of asymptomatic individuals was 19.9% among participants with antibodies and 49.7% among those without antibodies. All symptoms were reported more frequently by individuals with antibodies. The division of the prevalence of symptoms among individuals with antibodies by the prevalence among individuals without antibodies showed the following prevalence ratios: for changes in smell or taste (9.1), fever (4.2), tremors (3.9), breathing difficulty (3.2) and cough (2.8 times). Anosmia and fever were the symptoms with a greater capability to predict the presence of antibodies. CONCLUSION: The prevalence of symptoms was higher among individuals with antibodies against SARS-CoV-2. The proportion of asymptomatic individuals was low. Altered smell or taste and fever were the symptoms that most predict the presence of antibodies. These results can help to identify probable cases, contributing to the clinical diagnosis and screening of patients for testing and isolation guidance in positive cases, especially in scenarios of the scarcity of diagnostic COVID-19 tests.

Quality of Prenatal Care in Brazil: National Health Research 2013. / Qualidade do Pré-Natal no Brasil: Pesquisa Nacional de Saúde 2013.

This study aimed to assess the adequacy of prenatal care in Brazil associated with sociodemographic determinants. The study included a data analysis from the National Health Research performed in Brazil in 2013. Two outcomes on the adequacy of prenatal care were assessed: the Kessner index modified by Takeda index that, in addition to the former, assessed whether blood pressure and weight were measured in all appointments, as well as the performance of blood and urine tests and ultrasound. Both quality indicators were assessed for Brazil and for its macro-regions. According to Outcome 1, 80.6% of women received adequate prenatal care. When adding the performance of tests (Outcome 2), the rate dropped to 71.4%. Adequate prenatal care was more frequent among white women who performed prenatal care in the private health sector. The northern region had the lowest rate of adequate prenatal care, while the southeast region showed the highest rates. Despite the extensive coverage, prenatal care in Brazil still presents inequities and low service quality, especially for women from the poorest regions of the country.

O objetivo deste estudo foi avaliar a adequação do cuidado pré-natal no Brasil associado a determinantes sociodemográficos. A pesquisa consistiu em uma análise dos dados da Pesquisa Nacional de Saúde realizada no Brasil em 2013. Foram avaliados dois desfechos sobre a adequação do pré-natal, o índice de Kessner modificado por Takeda que, além de levar em consideração esse índice, avaliou se houve aferição da pressão arterial e do peso em todas as consultas, realização de algum exame de sangue e urina e ultrassom. Ambos indicadores de qualidade foram avaliados para o Brasil e também pelas macrorregiões do país. De acordo com o desfecho 1, 80,6% das mulheres realizaram o pré-natal adequado. Ao adicionarmos a realização de exames (Desfecho 2) o percentual foi 71,4%. O pré-natal adequado foi mais frequente entre as mulheres de cor branca e que realizaram o pré-natal na rede privada. A região norte apresentou as menores frequências de pré-natal adequado, enquanto a região sudeste as maiores. Apesar da ampla cobertura, o pré-natal no Brasil ainda apresenta iniquidades e baixa qualidade no atendimento, especialmente entre mulheres das regiões mais pobre do país.

Characteristics and prognosis of stage I-III breast cancer subtypes in Brazil: The AMAZONA retrospective cohort study.

OBJECTIVE: To describe stage I-III breast cancer (BC) molecular subtypes and outcomes among a cohort of patients from Brazil. METHODS: AMAZONA study is a retrospective cohort conducted from June 2008 to January 2009 including women of at least 18 years old, with histologically proven breast cancer, diagnosed in 2001 (n = 2198) and 2006 (n = 2714). In this analysis, we included patients who underwent surgery, had stage I-III disease and available pathological information (n = 2296). We estimated molecular subtypes by local immunohistochemical stains. Data was obtained from medical charts and public databases. RESULTS: Mean age at diagnosis was 54 years and 41.1% were younger than 50 years. 23.3% were diagnosed in stage I, 53.5% in stage II and 23.2% in stage III. 80.8% were treated in the public health system. 71.3% had hormonal receptor positive disease, 15.7% were HER-2 positive and 21.1% had triple-negative breast cancer. 55.6% were treated with mastectomy and 96.2% received adjuvant treatment (82.2% chemotherapy). 13.4% of HER-2 positive patients received adjuvant trastuzumab. Overall survival rate at 5 years was 96.84% for stage I, 94.16% for stage II and 70.48% for stage III. Molecular subtypes were independent prognostic factor in stages II and III patients. CONCLUSIONS: Brazilian women have a higher risk of being diagnosed with late stage breast cancer and younger age than in high-income countries. Luminal-like disease is the most common molecular subtype in the country. Triple negative and HER-2 positive had the worst prognosis.

Lung cancer in Brazil.

Lung cancer is one of the most incident types of cancer and a leading cause of cancer mortality in Brazil. We reviewed the current status of lung cancer by searching relevant data on prevention, diagnosis, and treatment in the country. This review highlights several issues that need to be addressed, including smoking control, patient lack of awareness, late diagnosis, and disparities in the access to cancer health care facilities in Brazil. We propose strategies to help overcome these limitations and challenge health care providers, as well as the society and governmental representatives, to work together and to take a step forward in fighting lung cancer.

Describing numerical variables: which are the most appropriate parameters to describe the data?

The proper description of numerical variables is very important when presenting a set of data. Measures of central tendency and dispersion are used to adequately understand a set of numerical variables. Knowledge of the properties of these measures and their adequate use provide the reader with a better understanding of the results of a study.

[Simultaneity of risk factors for chronic non-communicable diseases in the elderly in Pelotas, Rio Grande do Sul State, Brazil]. / Simultaneidade de fatores de risco para doenças crônicas não transmissíveis entre idosos da zona urbana de Pelotas, Rio Grande do Sul, Brasil.

This study aimed to describe the simultaneity of risk factors for chronic non-communicable diseases among the elderly (≤ 60 years) in a city in Southern Brazil. This was a cross-sectional, population-based study of 1,451 elderly in 2013. Cluster analysis was applied to selected risk factors (smoking, alcohol consumption, excess weight, and physical inactivity). Logistic regression was used to assess the association between simultaneity of risk factors and socio-demographic variables. The most frequent cluster in men (18.1%) and women (30.7%) was physical inactivity + excess weight. The cluster alcohol consumption + excess weight exceeded the expected level in men (O/E = 1.27; 95%CI: 1.01; 1.59) and women (O/E = 1.72; 95%CI: 1.35; 2.20). The presence of two or more risk factors in the elderly population (88.1%) points to the need for specific interventions for this population to fight risk factors simultaneously rather than separately.

Sampling: how to select participants in my research study?

BACKGROUND: In this paper, the basic elements related to the selection of participants for a health research are discussed. Sample representativeness, sample frame, types of sampling, as well as the impact that non-respondents may have on results of a study are described. The whole discussion is supported by practical examples to facilitate the reader's understanding. OBJECTIVE: To introduce readers to issues related to sampling.

Desempenho dos escores APACHE II e SOFA em pacientes com injúria renal aguda em uma unidade de terapia intensiva / Performance of APACHE II and SOFA scores in patients with acute kidney injury in an intensive care unit

Objetivo: Validar o desempenho dos escores APACHE II e SOFA para predizer a mortalidade em pacientes com injúria renal aguda em uma unidade de terapia intensiva. Métodos: Estudo observacional e retrospectivo realizado de janeiro de 2018 a setembro de 2020 em um hospital do Rio Grande do Sul. Foram incluídos 256 pacientes. Resultados: Ambos os escores apre- sentaram desempenho adequado para a discriminação da mortalidade em pacientes com injúria renal aguda (área sob a curva para APACHE II de 0,80 e para SOFA de 0,77). Conclusão: A injúria renal aguda é uma condição frequente em ambiente de unidade de terapia intensiva, e os resultados do presente estudo sugerem que ambos os índices são mais precisos quando aplicados em centros únicos e podem ser utilizados rotineiramente para predizer a mortalidade na população

Objective: To validate the performance of the APACHE II and SOFA scores to predict mortality in patients with acute kidney injury in an Intensive Care Unit. Methods: This is an observational and retrospective study conducted from January 2018 to September 2020 at a hospital in Rio Grande do Sul. A total of 256 patients were included. Results: Both scores showed adequate performance for the discrimination of mortality in acute kidney injury patients (area under the curve of 0.80 for APACHE II and 0.77 for SOFA). Conclusion: Acute kidney injury is a frequent condition in intensive care unit settings and the results of the present study suggest that both indices are more accurate when applied in single centers, and can be used routinely to predict mortality in the population

A Phase II Randomized Study of Lapatinib Combined With Capecitabine, Vinorelbine, or Gemcitabine in Patients With HER2-Positive Metastatic Breast Cancer With Progression After a Taxane (Latin American Cooperative Oncology Group 0801 Study).

BACKGROUND: Novel targeted agents and combinations have become available in multiple lines of treatment for human epidermal growth factor receptor 2-positive (HER2(+)) metastatic breast cancer (MBC). In this context, alternatives to the lapatinib (L) and capecitabine (C) regimen, evaluating L combined with other cytotoxic drugs, are warranted. PATIENTS AND METHODS: In the present phase II, multicenter study, patients with HER2(+) MBC with progression after taxane were randomized between L, 1250 mg, combined with C, 2000 mg/m(2) on days 1 to 14 (LC), vinorelbine (V), 25 mg/m(2) on days 1 and 8 (LV), or gemcitabine (G), 1000 mg/m(2) on days 1 and 8 (LG), every 21 days. The primary endpoint was the overall response rate. RESULTS: A total of 142 patients were included from 2009 to 2012. No differences were found in the patient baseline characteristics. The median age was 51 years, 69% were postmenopausal, 32% had liver metastasis, 57% were hormone receptor negative, and 48% had been previously treated with trastuzumab. The overall response rate was 49% (95% confidence interval [CI], 34.8%-63.4%), 56% (95% CI, 40%-70.4%), and 41% (95% CI, 27%-56.8%) in the LC, LV, and LG groups, respectively. The median progression-free survival was 9 months in the LC arm and 7 months in the other 2 arms (P = .28). The most common grade 3 and 4 adverse events were hand-foot syndrome (18%), diarrhea (6%), and increased alanine aminotransferase/aspartate aminotransferase (4%) in the LC arm; neutropenia (36%), diarrhea (9%), and febrile neutropenia (6%) in the LV arm; and neutropenia (47%), alanine aminotransferase/aspartate aminotransferase (13%), and rash (4%) in the LG arm. CONCLUSION: LV and LG seem to be active combinations in patients with HER2(+) MBC after taxane failure. The overall toxicity was manageable in all regimens.

Prevalence of symptoms of COVID-19 in the state of Rio Grande do Sul: results of a population-based study with 18,000 participants / Prevalência de sintomas característicos de covid-19 no Rio Grande do Sul: resultados de um estudo de base populacional com 18 mil participantes

ABSTRACT OBJECTIVE To evaluate the prevalence of reports of symptoms of COVID-19 among individuals with and without antibodies and identify those with greater capability to predict the presence of antibodies against SARS-CoV-2. METHODS The study uses data collected in phases 5 to 8 of Epicovid-19-RS. The presence of antibodies against SARS-CoV-2 was evaluated by a rapid test. The occurrence of cough, fever, palpitations, sore throat, difficulty breathing, changes in taste and smell, vomiting, diarrhea, body pain, shaking, and headache since March 2020 was also evaluated. Then, the capability to predict the evaluated symptoms concerning the presence of antibodies was calculated. RESULTS A total of 18,000 individuals were interviewed and 181 had antibodies against COVID-19 in phases 5 to 8. The proportion of asymptomatic individuals was 19.9% among participants with antibodies and 49.7% among those without antibodies. All symptoms were reported more frequently by individuals with antibodies. The division of the prevalence of symptoms among individuals with antibodies by the prevalence among individuals without antibodies showed the following prevalence ratios: for changes in smell or taste (9.1), fever (4.2), tremors (3.9), breathing difficulty (3.2) and cough (2.8 times). Anosmia and fever were the symptoms with a greater capability to predict the presence of antibodies. CONCLUSION The prevalence of symptoms was higher among individuals with antibodies against SARS-CoV-2. The proportion of asymptomatic individuals was low. Altered smell or taste and fever were the symptoms that most predict the presence of antibodies. These results can help to identify probable cases, contributing to the clinical diagnosis and screening of patients for testing and isolation guidance in positive cases, especially in scenarios of the scarcity of diagnostic COVID-19 tests.

RESUMO OBJETIVO Avaliar prevalência de relato de sintomas característicos de covid-19 entre indivíduos com e sem anticorpos e identificar aqueles com maior capacidade de predição da presença de anticorpos contra o SARS-CoV-2. MÉTODOS O presente estudo usa dados coletados nas fases de 5 a 8 do Epicovid-19-RS. A presença de anticorpos contra o SARS-CoV-2 foi avaliada por um teste rápido. Avaliou-se também a ocorrência dos sintomas tosse, febre, palpitações, dor de garganta, dificuldade para respirar, alterações no paladar e olfato, vômito, diarreia, dor no corpo, tremedeira e dor de cabeça, desde março de 2020. Então, calculou-se a capacidade de predição dos sintomas avaliados em relação a presença de anticorpos. RESULTADOS Nas fases de 5 a 8, 18 mil indivíduos foram entrevistados e 181 apresentaram anticorpos contra covid-19. A proporção de indivíduos assintomáticos foi de 19,9% entre participantes com anticorpos e 49,7% entre aqueles sem anticorpos. Todos os sintomas foram relatados com maior frequência por indivíduos com presença de anticorpos. A divisão da prevalência de sintomas entre indivíduos com anticorpos pela prevalência entre indivíduos sem anticorpos evidenciou as seguintes razões de prevalência: para alterações de olfato ou paladar (9,1), febre (4,2), tremedeira (3,9), dificuldade respiratória (3,2) e tosse (2,8 vezes). Anosmia e febre foram os sintomas com maior capacidade de predizer a presença de anticorpos. CONCLUSÃO A prevalência de sintomas foi maior entre indivíduos com anticorpos contra SARS-CoV-2. A proporção de indivíduos assintomáticos foi baixa. Alteração de olfato ou paladar e febre foram os sintomas que mais predizem a presença de anticorpos. Esses resultados podem auxiliar a identificação de casos prováveis, contribuindo para o diagnóstico clínico e triagem de pacientes para testagem e orientação de isolamento em casos positivos, especialmente em cenários de escassez de testes diagnósticos de covid-19.

The global conduct of cancer clinical trials: challenges and opportunities.

The nature of clinical research has changed substantially over the last 2 decades, evolving from being centered almost exclusively in developed countries to a more global scenario that is increasingly involving less developed regions of the world. Pharmaceutical companies and some academic cooperative groups have been conducting challenging, large pivotal registration studies with multinational participation. The much more needed globalization of academic research demands particular attention and represents a worthwhile subject for a more profound discussion. The requirement of large sample sizes and the potential for fast recruitment leading to a speedy completion of clinical studies are probably the most important factors that have fueled globalization of studies. Reduced operational costs and the ability to expedite the regulatory approval of drugs in various countries or regions are also important drivers. Globalization of research should be seen as having a much wider effect in the societies involved, in particular, when we consider public health, economic, social, and ethical implications. Most importantly, the process of expanding the network of clinical research sites also fosters the integration and the development of closer relationships among investigators at a global level. We consider this an essential element that should remain a prominent element in the discussion. In this article, we address the underlying reasons for globalization and we highlight some of the scientific and ethical concerns arising as a consequence. Finally, some strategies to address and mitigate the challenges of conducting multinational clinical research are proposed.

Test of association: which one is the most appropriate for my study?

BACKGROUND: Hypothesis tests are statistical tools widely used for assessing whether or not there is an association between two or more variables. These tests provide a probability of the type 1 error (p-value), which is used to accept or reject the null study hypothesis. OBJECTIVE: To provide a practical guide to help researchers carefully select the most appropriate procedure to answer the research question. We discuss the logic of hypothesis testing and present the prerequisites of each procedure based on practical examples.

Physical Activity at 11 Years of Age and Incidence of Mental Health Problems in Adolescence: Prospective Study.

AIM: To evaluate the longitudinal association between physical activity behavior at 11 years of age and the incidence of mental health problems from 11 to 15 years of age. METHODS: Individuals born in the city of Pelotas, Brazil, in 1993 have been followed up since birth. At 11 and 15 years of age, mental health was assessed using the Strengths and Difficulties Questionnaire (SDQ). At 11 years of age, physical activity was assessed through a validated questionnaire. The continuous SDQ score at 15 years was used as the outcome variable. The main exposure was physical activity behavior at 11 years of age divided into 3 categories (0, 1-299, ≥ 300 min/wk). RESULTS: The incidence of mental health problems from 11 to 15 years was 13.6% (95% CI, 12.4-14.9). At 11 years, 35.2% of the adolescents achieved 300 min/wk of physical activity. In the unadjusted analysis, physical activity was inversely related to mental health problems (P = .04). After adjustment for confounders, the association was no longer significant in the whole sample but was still significant among boys. CONCLUSION: Physical activity appears to be inversely related to mental health problems in adolescence, but the magnitude of the association is weak to moderate.

Breastfeeding and bone mass at the ages of 18 and 30: prospective analysis of live births from the Pelotas (Brazil) 1982 and 1993 cohorts.

OBJECTIVE: To evaluate the effect of total breastfeeding, breastfeeding duration and type of breastfeeding at 3 months of age on bone mass at 18 and 30 years. STUDY DESIGN: A prospective, longitudinal study was conducted with two birth cohorts (1982 and 1993) in Pelotas, Southern Brazil. Measurements of bone mineral content (BMC) and bone mineral density (BMD) at 18 and 30 years of age were obtained by dual-energy X-ray absorptiometry (DXA). Information on breastfeeding was collected during the first 4 years of life. Analyses were performed by linear regression and stratified by sex. RESULTS: A total of 1109 and 3226 participants provided complete information on breastfeeding in early life and bone mass at 18 and 30 years, respectively. No association between breastfeeding and bone mass was observed in women at both ages nor among men at age 30. Among men at the age of 18, BMC and BMD were higher among those breastfed regardless of duration (p=0.032 and p=0.043, respectively). CONCLUSIONS: Despite a very weak positive effect of breastfeeding (yes/no) on BMC and BMD at age 18 in men, most findings pointed to a lack of association between breastfeeding and bone mass until young adulthood.

Sample size: how many participants do I need in my research?

The importance of estimating sample sizes is rarely understood by researchers, when planning a study. This paper aims to highlight the centrality of sample size estimations in health research. Examples that help in understanding the basic concepts involved in their calculation are presented. The scenarios covered are based more on the epidemiological reasoning and less on mathematical formulae. Proper calculation of the number of participants in a study diminishes the likelihood of errors, which are often associated with adverse consequences in terms of economic, ethical and health aspects.