The epidemiology of abdominal adiposity : validation and application of ultrasonography to estimate visceral and subcutaneous abdominal fat and to identify their early life determinants

Obesity has become a major public health problem, and its prevalence has increased drastically worldwide over the last decades among all ages. Central adiposity, particularly visceral fat, may play a significant role in the development of obesity related co-morbidities such as diabetes. Accurate measures of both visceral and abdominal subcutaneous fat are essential for investigating the pathophysiology of obesity and its co-morbidities. However, anthropometry which is generally implemented in epidemiology to assess fat distribution, cannot distinguish between these two fat depots. Reference methods such as Magnetic Resonance Imaging (MRI) and Computer Tomography (CT) are often not feasible in large-scale epidemiological studies and in paediatric research due to ethical and practical issues. The aims of the thesis are: to assess the validity of ultrasound abdominal fat depths compared to MRI or CT measures of visceral fat and abdominal subcutaneous fat in populations covering a wide range of ages (from infancy to adulthood); to identify possible early life factors that may influence the quantity of these abdominal fat compartments. The findings of this thesis suggest that, ultrasonography is a suitable, non-invasive and reliable tool for quantifying abdominal fat compartments from infancy and it could be used to assess possible risk factors associated with obesity and related co-morbidities in a very early stage. The results from this thesis also indicate that during both intrauterine and postnatal periods, the accumulation of visceral and subcutaneous fat may be under different regulatory control. Early nutrition seems to contribute significantly to the quantity of these fat depots.