Objectives: This thesis investigated the body composition changes using dual-energy x-ray absorptiometry (DXA) in women in the midlife and beyond. The primary research question was whether changes in fat and lean mass over time are related to incident cardiovascular events. Previous studies have used surrogate anthropometric methods with inconsistent findings. The trends in total and regional fat and lean mass over a five-year period were documented. This study also compared the prevalence of obesity and metabolic risk factors using body mass index (BMI) and percentage body fat (PBF) against fat mass index (FMI) determined by DXA. Methods: This was a prospective, longitudinal observational study of women from ages 40 to 79 randomly recruited from the electoral roll and stratified into decades; 40-49, 50-59, 60-69 and 70-79 years. Clinical data and anthropometric measures were obtained. DXA was performed in Year 1 and Year 5. Total body mass (TBM), total fat mass (TFM), total lean mass, abdominopelvic fat mass, and appendicular fat and lean mass were determined. Incident cardiovascular events were recorded up to 12 years. Results: A total of 489 women completed DXA testing in Year 1 and Year 5. There were 437 (85.5%) participants remaining at the end of 12 years. Twelve died from cardiovascular causes, leaving a total of 449 participants (87.9%) available for analysis of body composition changes against incident cardiovascular events. There were significant increases in total body mass (TBM) (p<0.001), total fat mass (TFM) (p<0.01), total lean mass (p<0.05), arm fat mass (p<0.05), leg fat mass (p<0.001) and leg lean mass (p<0.05) within the 40-49 age decade. TBM, TFM and abdominopelvic fat started to decline from the 50-59 decade. Abdominopelvic fat reduction was significant from the 50-59 to later decades (p=0.05 to p<0.001). Arm lean mass showed significant reduction from the 50-59 decade (p<0.01). Leg lean mass declined later from the 60-69 decade, reaching significance in the 70-79 decade (p=0.05). There was a higher prevalence of obesity using PBF compared to BMI and FMI (p<0.001). This difference was greater from age 50-59 (p<0.05) which may be explained by age-related lean mass loss. PBF over-classified obesity in over 35% of normal and 95% of overweight categories compared to FMI and BMI. BMI has a sensitivity of 78.9% and specificity of 98.3% for obesity using FMI as the standard. There was no difference in diabetes, dyslipidaemia, hypertension and metabolic syndrome prevalence within the BMI-obesity and FMI-obesity categories (p>0.05). A 10% or greater decrease in total fat mass index was associated with a 67% lower likelihood for any cardiovascular event (OR=0.33), with no association for an increase. A 10% or greater decrease in abdominal fat mass index was associated with a 62% lower likelihood of incident stroke (OR=0.38), with no association for an increase. A 10% or greater decrease in appendicular lean mass index resulted in increased odds ratio of 2.91 for incident peripheral artery events (OR=2.91). Conclusion: TFM and abdominopelvic fat were found to decline earlier from the 50-59 age decade than previous literature would suggest. A reduction in total and abdominal fat mass for women in midlife and beyond was associated with significant reduction in risk of incident cardiovascular events. An increase in fat mass did not contribute to additional cardiovascular events. A decline in appendicular lean mass with age occurred from the 50-59 decade with earlier and greater loss in the arms. A reduction in limb muscle mass may be an independent marker for cardiometabolic risk and peripheral artery disease. Health interventions including reducing fat mass and maintaining physical activity remain of value to modify the risk of cardiovascular events for women in the midlife and beyond. PBF classified more obesity than BMI and FMI because of its low pre-determined threshold. BMI had the lowest sensitivity for obesity diagnosis. There was no significant difference in the prevalence of metabolic risk factors between BMI and FMI-obesity categories indicating that fat location may influence metabolic dysregulation. No independent association was found using anthropometric measurements and incident cardiovascular events. DXA may be an accessible clinical tool to assess body composition and provide a measure of risk for future cardiovascular events. Further investigations are required to support more widespread application for cardiovascular risk particularly in men and other ethnic groups.