Le but de cette thèse était d'explorer les relations entre le niveau de performance physique, le niveau d'activité physique usuel, les apports nutritionnels, les caractéristiques anthropométriques et le sommeil d'un côté et la densité minérale osseuse, la géométrie osseuse de la hanche et le trabecular bone score (TBS) de l'autre chez les jeunes adultes Libanais et Français agés de 18 à 35 ans. Dans un premier temps, nous avons mené 10 études préliminaires chez les jeunes adultes Libanais. Ces études ont montré que le poids, la masse maigre, la pratique d'activités physiques à impacts, la force maximale et le niveau de puissance musculaire sont des déterminants positifs de la DMO et que la pratique d'activités physiques à impats influence positivement les valeurs de TBS, les indices géométriques de résistance osseuse de la hanche (surface de la section transversale (CSA) et module de section (Z)) et les indices de résistance osseuse du col fémoral (Bending strength index (BSI), compressive strength index (CSI) et impact strength index (ISI)). Ces études préliminaires ont aussi montré des corrélations entre les apports protéiques et calciques d'une part et la DMO d'autre part chez les jeunes hommes. A la fin, une des études préliminaires a suggéré que la qualité de sommeil est associée à une meilleure DMO chez les jeunes hommes. Dans un deuxième temps, nous avons mené une étude sur 535 jeunes adultes français (342 femmes et 193 hommes) afin d'explorer les relations entre le niveau de performance physique, le niveau d'activité physique, la composition corporelle, les apports nutritionnels et la qualité du sommeil d'une part et les valeurs de BUA (Broadband Ultrasound Attenuation) d'autre part. Cette étude a montré que les caractéristiques anthropométriques (poids, IMC, masse grasse, tour de taille et tour de hanche) sont des facteurs corrélables à la BUA chez les femmes mais pas chez les hommes. D'autre part, il y avait une tendance de corrélation positive entre la performance en détente verticale et la BUA chez les hommes. En conclusion, cette thèse a pu définir un nombre important de facteurs corrélables à la BUA, à la DMO, à la géométrie osseuse et au TBS et a ainsi permis d'identifier de nouvelles relations entre les déterminants de santé et les paramètres osseux chez les jeunes adultes. / The aim of this study was to investigate the relations between physical performance level, physical activity level, nutritional intakes, anthropometrical characteristics and sleep on the one hand and bone mineral density, hip geometric indices and trabecular bone score (TBS) on the other hand in young Lebanese and French subjects aged to 18 to 35 years. In a first step, we led 10 preliminary studies in young Lebanese adults. These studies have shown that body weight, lean mass, high-impact physical activity practice, maximal strength and muscular power are positive determinants of bone mineral density, and that high-impact physical activity practice positively influences TBS values, geometric indices of hip bone strength (cross-sectional area (CSA) and section modulus (Z)) and femoral neck strength indices (Bending strength index (BSI), compressive strength index (CSI) and impact strength index (ISI)). These preliminary studies have also shown positive correlations between nutritional intakes (daily calcium intakes and daily protein intakes) and BMD values in young Lebanese men. Finally, one of these preliminary studies has shown that sleep quality is associated with a greater BMD in young men. In a second step, we led a study on 535 young French adults (342 women and 193 men) to explore the relations between physical performance level, physical activity level, nutritional intakes, anthropometrical characteristics and sleep on the one hand and BUA (Broadband ultrasound attenuation) values on the other hand. This study has showed that anthropometric characteristics (body weight, body mass index, waist circumference and hip circumference) are positively correlated to BUA values in women but not in men. On the other hand, we have noted a tendency of positive relation between vertical jump performance and BUA values in men. In conclusion, this thesis has defined an important number of factors significantly correlated to BUA, BMD, hip geometric indices and TBS and therefore permitted to identify new relations between health determinants and bone parameters in young adults.

Title: The influence of a specific movement therapy for bone density in female patients evaluated by bone DXA densitometry Objectives: The aim was to demonstrate the positive impact of movement on bone mineral density in patients suffering from postmenopausal osteoporosis. Summary: The main topic of this thesis is to evaluate potential benefits of an intensive program to the treatment of patients suffering from postmenopausal osteoporosis treated with the standard pharmacological therapy. The marker determined to evaluate the effect of change in bone density was DXA bone densitometry in the standard locations (lumbar spine, proximal femur). The evaluation of measurement results was performed after six-month program. Methods: The experiment, which was the substantial part of this thesis, was based on the method of comparison of input and output values in experimental and control groups. Each group consisted of 15 patients. Measured parameters of bone density were deliberately affected by means of physical interventions in the experimental group of patients. The results were processed and evaluated by Microsoft Excel and SAS 9. 2 programs. Results: Physical intervention is an essential part of therapy in patients suffering from postmenopausal osteoporosis. The experiment proved that a six-month...

Introdução - Nos últimos anos diversas hipóteses foram investigadas sobre a relação entre gordura corporal e a massa óssea. Objetivo - O presente estudo visa avaliar a associação de índices de gordura corporal e massa óssea em adultos e idosos. Metodologia - O estudo foi desenvolvido com os dados obtidos do estudo transversal de base populacional intitulado Inquérito Domiciliar de Saúde no Município de São Paulo (ISA Capital 2015), realizada de janeiro de 2015 a maio de 2016. A amostra foi composta por 296 indivíduos, sendo 129 adultos (18 a 59 anos) e 167 idosos (60 anos ou mais), de ambos os sexos. Utilizando os dados antropométricos, foram calculados os índices: Índice de Massa Corpórea (IMC), Índice de Conicidade (IC), Índice de Circularidade Corporal (ICC), Índice de Formato Corporal (IFC), Índice de Adiposidade Corporal (IAC), Índice de Gordura Corporal (IGC) e Índice de Adiposidade Visceral (IAV). Além disso, foram avaliados os dados de gordura corporal (GC) em kg, gordura visceral (GV em gramas), porcentagem de gordura corporal ( por centoGC) e densidade mineral óssea de corpo total (DMO CT), coluna lombar (DMO L1- L4) e do colo do fêmur (DMO femoral), obtidos pelo DXA (modelo Lunar iDXA Advance, GE Healthcare, Madison, WI, USA). Foram calculadas estatísticas descritivas (média, desvio-padrão, percentis); a normalidade foi testada por Anderson- Darling, foi aplicado o teste Mann-Whitney e a correlações de Spearman. A GC (kg) foi ajustada por sexo e idade e a DMO CT, L-L4 e femoral foram ajustadas por gênero, classe etária, atividade física, ingestão de álcool e tabagismo com o uso de Modelos Lineares Generalizados. Uma vez identificado o modelo mais adequado a uma variável resposta, procurou-se reduzir o número de parâmetros com uso do Critério de Informação Akaike (AIC). Para realizar essas análises foi utilizado o software SPSS, 23.0 (SPSS Inc, Chicago IL, USA) e R (Projeto para estatística em sistema computacional) for Windows, versão 3.4.1. O nível de significância adotado foi de 5 por cento. Resultados - No artigo 1 é apresentado uma revisão sobre a relação entre os índices antropométricos e de gordura corporal com Doenças Crônicas Não-Transmissíveis (DCNT) como diabetes mellitus, hipertensão arterial sistêmica, síndrome metabólica entre outras. No artigo 2, foi observado baixa proporção de osteoporose nos participantes. Na relação entre os índices antropométricos com a GC (kg), verificamos que com exceção do IFC e IAV, os demais índices apresentaram correlação positiva e significante com a GC em kg (p<0,001). Entretanto, o modelo que apresentou o melhor ajuste e associação para a GC foi o IGC (89,97 por cento), seguido do IMC (83,93 por cento). Na associação dos índices com a DMO nos 3 sítios (DMO CT, L-L4 e femoral), observamos baixos valores de predição dos modelos avaliados, sendo que o modelo que apresentou melhor associação foi o IMC para DMO femoral. Conclusão O índice antropométrico que mais se aproximou da GC (kg) foi o IMC, como observado na análise de correlação e confirmado na análise inferencial, uma vez que as fórmulas para obtenção de ambos os índices são muito semelhantes. Na relação com a DMO, nenhum índice antropométrico é capaz de predizer a DMO nos 3 sítios avaliados na amostra estudada. / Introduction - In recent years several hypotheses have been investigated on the relationship between body fat and bone mass. Objective - The present study aims to evaluate the association of body composition indexes and bone mass in adults and the elderly. Methods - The study was conducted in a subsample from the populationbased cross-sectional study titled Health Study of São Paulo (ISA-Capital Study- 2015), held from january 2015 to may 2016. This 396 individuals, 129 adults (18 to 59 years) and 167 elderly (60 and over), of both sexes. Data on demographic, anthropometric [weight (kg), height (m), waist circumference and hip (cm)], body composition (body fat distribution) and bone (bone mineral density and composition) analyzed. The ratios was calculated, ranked and analyzed: Body Mass Index (BMI), Body Adiposity Index (BAI), Body Roundness Index (BRI), a Body Shape Index (ABSI) and the Conicity Index (C index) and as a comparison method was the Fat Mass Index (FMI) obtained by DXA. Bone mineral density (BMD) was evaluated in the lumbar spine L1-L4 and femoral neck through energy dual beam absorptiometry technique, issued by an X-ray source - DXA (dual-energy X-ray absorptiometry) Lunar model iDXA Advance (GE Healthcare, Madison, WI, USA). Descriptive statistics (mean, standard deviation, percentiles) were calculated; the normality was tested by Anderson-Darling, thus the Mann-Whitney test and Spearman correlations were applied. The BF (kg) was adjusted by gender and age and the CT, L-L4 and femoral BMD were adjusted for gender, age group, physical activity, alcohol intake e smoking, with the use of Generalized Linear Models. Once the most appropriate model was identified for a response variable, we attempted to reduce the number of parameters using the Akaike Information Criterion (AIC). The SPSS software, 23.0 (SPSS Inc, Chicago IL, USA) and R (Computer statistical system design) for Windows, version 3.4.1 for data analysis were used. The level of significance was set at 5 per cent. Results - In article 1, it presents revision about the relationship between anthropometric and body fat indexes with chronic-degenerative diseases (CDC) such as diabetes mellitus, systemic arterial hypertension, metabolic syndrome, among others. In article 2 a low proportion of osteoporosis was observed in the participants. In the relationship between the anthropometric indices with the BF (kg), we observed that, with the exception of the IFC and VAI, the other indexes presented a positive and significant correlation with the BF in kg (p <0.001). However, the model that presented the best fit and association for BF was FMI (89.97 per cent), followed by BMI (83,93 per cent). In the association of the indexes with BMD in the 3 sites, we observed low values of prediction of the models evaluated, and the model that presented the best association was the BMI for femoral BMD. Conclusion - The anthropometric index that most approached the BF (kg) was BMI, as observed in the correlation analysis and confirmed in the inferential analysis, since the formulas to obtain both indices are very similar. In relation to BMD, no anthropometric index is able to predict BMD at the 3 sites evaluated in the studied sample.

Les buts de cette thèse étaient d’évaluer les taux de 25(OH)D chez des jeunes adultes Libanais et d’explorer les relations entre la 25(OH)D, la vitamine D libre et plusieurs paramètres osseux dans la même population. Dans un premier temps, nous avons démontré que l’insuffisance en 25(OH)D est très fréquente chez les jeunes adultes libanais (66 % des femmes vs. 50,7 des hommes) et que les taux de 25(OH)D ne sont pas des déterminants positifs de la DMO. Dans un deuxième temps, nous avons démontré que la 25(OH)D était positivement corrélée au BSI et au CSI dans les deux sexes et que certaines de ces corrélations ont persisté même après ajustement pour l’IMC. Dans un troisième temps, nous avons démontré que les taux de 25(OH)D sont positivement corrélés au TBS dans les deux sexes et que les valeurs de TBS sont supérieures chez les sujets ayant des taux suffisants (> 30 ng/ml) en 25(OH)D par rapport aux sujets ayant des taux insuffisants (< 30 ng/ml) en 25(OH)D. Dans un dernier temps, la vitamine D libre était positivement corrélée à plusieurs paramètres osseux dans les deux sexes ; certaines corrélations ont persisté même après ajustement pour le poids corporel. En conclusion, la 25(OH)D est un déterminant positif de plusieurs paramètres osseux chez les jeunes adultes Libanais. De plus, la vitamine D libre semble être un déterminant positif de plusieurs paramètres osseux dans cette population. La mesure des deux formes de vitamine D (25(OH)D et vitamine D libre) est intéressante pour l’évaluation et la prévention de l’ostéoporose. / The aims of this study were to evaluate the levels of 25(OH)D in a group of young Lebanese adults and to explore the relations between 25(OH)D, free vitamin D and many bone parameters in the same population. First, we have demonstrated that vitamin D insufficiency is very frequent in young Lebanese adults (66% in women vs. 50.7 % in men) and that levels of 25(OH)D are not positive determinants of BMD. Second, we have shown that 25(OH)D was positively correlated to BSI and CSI in both sexes, and some of these correlations remained significant after adjustment for BMI. Third, we have demonstrated that 25(OH)D levels were positively correlated to TBS in both sexes and that TBS values were higher in vitamin D sufficient (> 30 ng/ml) subjects compared to vitamin D insufficient subjects (< 30 ng/ml). Finally, free vitamin D was positively correlated to many bone parameters in both sexes; some of these correlations remained significant after adjustment for body weight. In conclusion, 25(OH)D is a positive determinant of many bone parameters in young Lebanese adults. Moreover, free vitamin D seems to be a positive determinant of many bone parameters in this population. The measurement of both forms of vitamin D (25(OH)D and total vitamin D) is interesting for the evaluation and the prevention of osteoporosis.

A osteoporose é um distúrbio esquelético caracterizado pela diminuição da força óssea, resultando em um risco aumentado de fratura. A perda óssea ocorre tanto em mulheres como em homens devido ao processo de envelhecimento natural [Drake et al.,2015]. De acordo com o diagnóstico e classificação da Organização Mundial da Saúde (OMS), a osteoporose é definida pela densidade mineral óssea (DMO) na coluna lombar ou quadril inferior a -2,5 do desvio padrão abaixo da média da DMO para uma população de jovens adultos [Cosman et al., 2014]. Tem uma alta prevalência sendo mais freqüente do que a soma de casos de infarto do miocárdio, câncer de mama e acidente vascular cerebral. Essa doença deve ser considerada como um problema de saúde pública, pois afeta o indivíduo em sua função social, física e de trabalho e, portanto, causa impacto socioeconômico [Haddad et al.,2015]. Neste trabalho, desenvolvemos um novo modelo de osteoporose em ratos nude por ooforectomia visando o uso de células humanas para a Medicina Traslacional. Para tanto, foram estabelecidos dois passos e a osteoporose foi analisada por densitometria óssea aos 0, 21, 45 e 60 dias após a cirurgia e por análises histológicas de ossos femorais, i) padronização do modelo animal de osteoporose por ooforectomia, utilizando ratos Sprague-Dawley fêmeas de 12 semanas; ii) na segunda fase do projeto, a osteoporose foi induzida em ratos imunodeficientes nude Rowett fêmeas (NTacFCfiq: NIJ-Whn) de 12 semanas e os mesmos ensaios foram conduzidos para detectar a osteoporose. O soro foi coletado para a medida de estrogênio. As análises da DMO e histológicas mostraram modificação do contéudo mineral e ósseos e da estrutura óssea, respectivamente, aos 60 dias após a cirurgia em ambas as linhagens de ratos fêmeas. Com este trabalho, pretendemos contribuir para a compreensão da biologia da osteoporose utilizando um novo modelo animal, o que pode levar ao desenvolvimento de novos protocolos clínicos e terapêuticos no futuro. / Osteoporosis is a skeletal disorder characterized by decreased bone strength resulting in an increased risk of fracture. Bone loss occurs in both women and men due to the natural aging process [Drake et al.,2015]. According to the World Health Organization (WHO) diagnosis and classification, osteoporosis is defined by the bone mineral density (BMD) in the hip or lumbar spine being less than or equal to -2.5 of the standard deviation below the BMD average for a population of young adults [Cosman et al.,2014]. It has a high prevalence being more frequent than the sum of cases of myocardial infarction, breast cancer and stroke. This disease should be considered as a public health problem, since it affects the individual in his social, physical and work function and, therefore, causes socioeconomic impact [Haddad et al.,2015]. In this work, we developed a new rat model of osteoporosis by oophorectomy aiming the use of human cells for Traslational Medicine. To this end, two steps were established, i) standardization of the animal model of osteoporosis by oophorectomy, using female Sprague-Dawley rats at 12 weeks. The osteoporosis was analyzed by bone densitometry at 0, 21, 45 and 60 days after surgery and by histological analyzes of femoral bones. The serum was collected for measurement of estrogen markers; ii) at second stage of the project, osteoporosis was induced in immunodeficient female nude Rowett (NTacFCfiq: NIJ-Whn) at 12 weeks and the same assays were conducted to detect osteoporosis. Bone mineral density and bone histological analyzes showed changes in the of bone mineral content and bone structure, respectively, at 60 days after surgery in both rat lineages. With this work, we intend to contribute to the understanding of osteoporosis biology using a new animal model, which can lead to the development of new clinical and therapeutic protocols in the future.

Osteoporosis is a disease characterized by low bone mineral density, deteriorated bone microstructure and increased fracture risk. About 50% of all women and 25% of all men will have an osteoporotic fracture. Given that there is no effective cure in established osteoporosis, prevention is of high importance. Bone mineral density (BMD) is accumulated during childhood and adolescence with a peak at about 20 years of age. Peak BMD has been suggested to explain at least half of the variation in BMD up to old age. Thus, to increase peak BMD could decrease the risk of later fractures. The purpose of the present thesis was to investigate the influence of physical activity, vitamins A and D, and fatty acids on peak bone mass in men. The influence of physical activity on bone accrual was studied in two cohorts. In the first cohort 46 ice hockey players, 18 badminton players and 27 controls, all 17 years of age at baseline, were followed for four years. During the follow up the badminton players gained more bone mass at the hip compared to both the ice hockey players and controls. In the second cohort the associations between physical activity and BMD were investigated in 62 female and 62 male young medical students. The estimated high impact activity per week was associated with bone mass at all sites in the male medical students (r=0.27-0.53, p&lt;0.05). In the female cohort different estimates of physical activity were not related to bone mass at any site. In both males and females correlations between bone mass and body constitution parameters were observed. Levels of vitamin D3, vitamin D2, retinol, retinol-binding-protein-4 (RBP-4) and fatty acids were measured in 78 young men with a mean age of 22.6 years. BMD at various sites were measured using Dual-Energy X-ray absorptiometry. Levels of vitamin D3 showed a significant positive association with all BMD sites and also lean body mass (r=0.23-0.35, p&lt;0.05). Levels of vitamin D2, however, showed a significant negative correlation with BMD of the total body (r=-0.28, p=0.01) and spine (r=-0.27, p=0.02). There was also a significant negative relationship between levels of vitamin D3 and D2 (r=-0.31, p=0.006). Concentrations of n-3 (omega-3) fatty acids showed a positive association with BMD at the total body (r=0.27, p=0.02) and spine BMD (r=0.25, p=0.02). There was also a positive association between levels of n-3 fatty acids and changes in BMD of the spine between 16 and 22 years of age (r=0.26, p=0.02). The significant associations found seemed to be related mostly to the concentration of the n-3 fatty acid docosahexaenoic acid. Levels of retinol and RBP-4 were not related to BMD but to levels of osteocalcin, which is a marker of bone formation. This association disappeared when adjusting for the influence of abdominal fat mass. In summary, the present thesis suggests that many modifiable factors may influence the accumulation of peak bone mass in males, such as physical activity, vitamins, and fatty acids. Further studies are needed to investigate whether optimizing these factors in youth may decrease the risk of osteoporosis later in life.

Ontogenetic patterns in postcranial robusticity are analysed in the skeletons of eighty-two juvenile Later Stone Age hunter-gatherers with estimated ages at death ranging from infancy to late adolescence. Robusticity is quantified from cross-sectional geometric properties of diaphyses at sixteen sites throughout the skeleton, using radiography and casting methods. Skeletal growth profiles for strength measures are analysed with locally-weighted regression and additional curve fitting to evaluate developmental trajectories. Ethnographic accounts of infancy and childhood in modern Ju/'hoansi (Khoesan) communities provide a culturally-relevant interpretive framework for evaluating skeletal correlates of behaviour. This research demonstrates that bone strength properties can be functionally linked to behaviour among juveniles toward the reconstruction of patterns of physical activity among prehistoric children. Postcranial strength measures vary predictably with age such that developmental patterns and timing in appositional growth can be assessed reliably. The onset of walking among Later Stone Age juveniles is evident by two years of age from proportional lower to upper limb strength measures. The lower limb continues to adapt to increasing loading demands especially in response to torsional forces, and bending in the medio-lateral plane; biomechanical shape measures illustrate the gradual development of the femoral pilaster. Individual humeral strength is symmetrical with respect to the orientation maximal bending forces experienced throughout development, but the magnitude of the functional adaptive response is greater, on average, in the right limb with more than 70% of the sample over the age of six displaying right-side dominance. Humeral asymmetry and side dominance does not emerge until late childhood, and the majority of arm strength is accrued during adolescence, relative to the sex-combined mean values for Later Stone Age adults. Evidence for sexual dimorphism in upper limb properties is evident by late adolescence whereas sex-based patterns of mobility reflected in lower limb strength have yet to emerge. These results illustrate the developmental patterns that underlie postcranial markers of subsistence activities in Later Stone Age hunter-gatherers.

Ontogenetic patterns in postcranial robusticity are analysed in the skeletons of eighty-two juvenile Later Stone Age hunter-gatherers with estimated ages at death ranging from infancy to late adolescence. Robusticity is quantified from cross-sectional geometric properties of diaphyses at sixteen sites throughout the skeleton, using radiography and casting methods. Skeletal growth profiles for strength measures are analysed with locally-weighted regression and additional curve fitting to evaluate developmental trajectories. Ethnographic accounts of infancy and childhood in modern Ju/'hoansi (Khoesan) communities provide a culturally-relevant interpretive framework for evaluating skeletal correlates of behaviour. This research demonstrates that bone strength properties can be functionally linked to behaviour among juveniles toward the reconstruction of patterns of physical activity among prehistoric children. Postcranial strength measures vary predictably with age such that developmental patterns and timing in appositional growth can be assessed reliably. The onset of walking among Later Stone Age juveniles is evident by two years of age from proportional lower to upper limb strength measures. The lower limb continues to adapt to increasing loading demands especially in response to torsional forces, and bending in the medio-lateral plane; biomechanical shape measures illustrate the gradual development of the femoral pilaster. Individual humeral strength is symmetrical with respect to the orientation maximal bending forces experienced throughout development, but the magnitude of the functional adaptive response is greater, on average, in the right limb with more than 70% of the sample over the age of six displaying right-side dominance. Humeral asymmetry and side dominance does not emerge until late childhood, and the majority of arm strength is accrued during adolescence, relative to the sex-combined mean values for Later Stone Age adults. Evidence for sexual dimorphism in upper limb properties is evident by late adolescence whereas sex-based patterns of mobility reflected in lower limb strength have yet to emerge. These results illustrate the developmental patterns that underlie postcranial markers of subsistence activities in Later Stone Age hunter-gatherers.

Despite usual onset during adolescence the cause of low bone density in adolescent onset anorexia nervosa is incompletely understood. Puberty is known to be a crucial time for the development of peak bone mass, due principally to growth plate bone formation and modelling on preformed surfaces. This results in bone formation uncoupled from bone resorption leading to increased bone size due to increase in matrix and bone mineral content. It was hypothesized that low bone density in adolescent anorexia nervosa was caused by malnutrition during puberty suppressing normal bone matrix formation at all sites of bone formation thus arresting bone mineralization. Method 49 female adolescents with anorexia nervosa and 109 healthy female adolescent controls were studied. 22 of the anorexia nervosa subjects were studied again a year later. Bone area, mineral content and density were measured using Dual Xray Absorptiometry at the spine, hip and whole body sites, including body composition assessment. Estimated volumetric bone density was calculated using published equations in order to study bone density independent of bone size. Height, weight and Tanner stage in puberty were measured. Dietary intake and physical exercise were assessed using questionnaires. In a subset of anorexia nervosa and control subjects bone age was measured. In a subset of anorexia nervosa subjects bone formation was assessed using serum bone specific alkaline phosphatase and osteocalcin, and bone resorption was assessed using urine N-telopeptide.

Introdução: Com o aumento da expectativa de vida dos pacientes com Fibrose Cística (FC), a saúde óssea têm sido objeto de estudo a fim de otimizar a qualidade de vida desses pacientes. A prevalência de massa óssea baixa e os fatores de risco associados são altamente variáveis dependendo da população estudada. Objetivos: Determinar a prevalência de massa óssea baixa em pacientes adolescentes e adultos com FC e estudar os fatores potencialmente associados. Métodos: Densidade mineral óssea foi determinada por DXA na coluna lombar em todos os pacientes e no fêmur em pacientes ≥20 anos. Avaliações nutricionais, bioquímicas e pulmonares foram realizadas. Dados referentes ao tratamento farmacológico foram coletados. Resultados: 58 pacientes foram incluídos no estudo (25 homens/ 33 mulheres), média de idade de 23,9 anos (16-53). Massa óssea baixa foi verificada em 20,7% dos pacientes. Não houve histórico de fratura. Z-score da coluna lombar associou-se positivamente com IMC (r= 0,3; p= 0,022), VEF1% (r=0,415; p=0,001). A média do Z-score da coluna foi mais alta nas mulheres que nos homens (p=0,001), em pacientes que não possuíam insuficiência pancreática (p=0,02) e em pacientes que não haviam sido hospitalizados no período de três meses (p=0,032). Os fatores encontrados como preditores independentes de Z-score da coluna lombar foram sexo masculino e IMC. Conclusão: Massa óssea baixa é frequente em pacientes com FC e está associada ao IMC, o qual provavelmente reflete a severidade da doença, e ao sexo masculino. Esforços devem ser empreendidos com o objetivo de manter esses pacientes com perfil nutricional adequado. / Background: Survival of cystic fibrosis (CF) patients has increased, so bone health could be important for the quality of life of affected patients. Several studies described lower bone mass density (BMD) in patients with CF, which increased fracture risk. Objective: The aim of this study was to evaluate the prevalence of low BMD as well as to evaluate the factors associated with bone mass in these patients. Methods: BMD was measured by DXA in lumpar spine (L1-L4), in patients ≤19years-old, or lumbar spine and femur (total and neck) in patients ≥20years-old. Evaluations of nutritional status, biochemical parameters and lung function were performed. Medications were obtained from medical records Results: Fifty-eight patients were included in the study (25 males/33females), mean age 23.9 years (16-53). The prevalence of bone mass below the expected range for age at any site was 20.7%. None of the subjects had history of fracture. Lumbar spine Z-score in FC patients correlated positively with BMI (r= 0.3, p=0.001), and with FEV1 (%predicted) (r=0.415, p=0.022). Mean lumbar spine Z-score were higher in women (p=0.001), in patients with no pancreatic insufficiency (p=0.032), and in patients with no hospitalization in the last 3 months (p=0.02). BMI (p= 0.001) and sex (p=0.001) were independently associated with the Z-score in the lumbar spine. Conclusion: Low bone mass is a frequent problem in patients with CF, being associated with BMI, which could reflect disease intensity, and male sex. A larger effort should be made to keep these patients well-nourished.