Timothy A. Welborn

Multiple regression analysis of risk factors for cardiovascular disease and cancer mortality in Busselton, Western Australia—13-year study

The mortality of 1564 Busselton subjects has been studied from 1966-79 to determine whether risk factors for cardiovascular disease (CVD) and coronary heart disease (CHD) showed any change in emphasis compared with the Framingham Population Study of 20 yr previously. The Busselton analysis used subjects free of probable and suspect coronary heart disease at onset. In men aged 40-59, systolic blood pressure (SBP), forced expiratory volume (FEV), and serum cholesterol levels were significant independent determining variables for CVD mortality and cholesterol for CHD mortality, with SBP being related to CVD in men aged 60-74 yr. In women, there were few indicators of future vascular risk with no significant determining variable for CVD and CHD in 40-59 yr olds, but blood glucose and FEV were significant risk factors for CVD in women aged 60-74 yr. Cholesterol was unrelated to mortality in women but showed negative relationship with cancer in 60-74 yr old men. In total mortality, smoking in men and women, and obesity in women were significant risk factors; 1 hr serum insulin had a negative relationship in men aged 40-59 yr, and a stronger positive relationship in men aged 60-74 yr, but this may have been due to the close negative association of the variable with body size (i.e. height). More studies are required to ascertain whether glucose and insulin have an aetiological role in vascular disease.

Familial correlations, cohabitation effects, and heritability for cardiovascular risk factors

Familial correlations in cardiovascular risk factors were investigated with use of data from a community-based sample of 1319 nuclear families involving 4178 adult persons collected in the Busselton Population Health Surveys over the period 1966 to 1981. The risk factors considered were systolic blood pressure, diastolic blood pressure, body mass index, triceps fatfold, and cholesterol. All risk factors showed positive familial correlations, with correlations generally being lower for spouses than for parent-offspring pairs or for siblings. Spouse correlations showed little variation with age, suggesting that observed correlations are primarily due to assortative mating and not to cohabitation. The parent-offspring correlations tended to decline with age of (adult) offspring; this observation suggests that the effect of a shared household environment during childhood and adolescence diminishes over time when living apart during adulthood. The sibling correlations decreased with age for blood pressure and serum cholesterol and increased with age for body mass index and triceps fatfold. The estimated heritabilities were 27% for systolic and diastolic blood pressure, 37% for serum cholesterol, 52% for body mass index, and 23% for triceps fatfold. These results confirm that substantial familial aggregation of cardiovascular risk factors occurs and that much of this aggregation has a genetic basis, although assortative mating (in spouses) and environmental influences (in offspring and siblings) are also present. The nuclear family should be considered as a point of intervention in cardiovascular disease prevention programs.

Anthropometric measurements of general and central obesity and the prediction of cardiovascular disease risk in women: a cross-sectional study.

Objectives It is important to ascertain which anthropometric measurements of obesity, general or central, are better predictors of cardiovascular disease (CVD) risk in women. 10-year CVD risk was calculated from the Framingham risk score model, SCORE risk chart for high-risk regions, general CVD and simplified general CVD risk score models. Increase in CVD risk associated with 1 SD increment in each anthropometric measurement above the mean was calculated, and the diagnostic utility of obesity measures in identifying participants with increased likelihood of being above the treatment threshold was assessed. Design Cross-sectional data from the National Heart Foundation Risk Factor Prevalence Study. Setting Population-based survey in Australia. Participants 4487 women aged 20–69u2005years without heart disease, diabetes or stroke. Outcome measures Anthropometric obesity measures that demonstrated the greatest increase in CVD risk as a result of incremental change, 1 SD above the mean, and obesity measures that had the greatest diagnostic utility in identifying participants above the respective treatment thresholds of various risk score models. Results Waist circumference (WC), waist-to-hip ratio (WHR) and waist-to-stature ratio had larger effects on increased CVD risk compared with body mass index (BMI). These central obesity measures also had higher sensitivity and specificity in identifying women above and below the 20% treatment threshold than BMI. Central obesity measures also recorded better correlations with CVD risk compared with general obesity measures. WC and WHR were found to be significant and independent predictors of CVD risk, as indicated by the high area under the receiver operating characteristic curves (>0.76), after controlling for BMI in the simplified general CVD risk score model. Conclusions Central obesity measures are better predictors of CVD risk compared with general obesity measures in women. It is equally important to maintain a healthy weight and to prevent central obesity concurrently.

Self-reported health and use of health services: a comparison of diabetic and nondiabetic persons from a national sample

Abstract: Population‐based epidemiological and health service utilisation information on diabetes and other noncommunicable diseases is still scarce in Australia. Such information is needed by health economists, policy makers and service providers. Data from the 1989–90 National Health Survey conducted by the Australian Bureau of Statistics have been used to obtain estimates of the prevalence of cardiovascular morbidity, lifestyle factors, use of hospital and medical services, and self‐assessed health and happiness for Australian persons with diabetes. Prevalences are compared with those for persons without diabetes. Those with diabetes had two to three times the prevalence of most cardiovascular conditions, similar levels of exercise (except for diabetic women over 40 years of age who exercised less than their nondiabetic counterparts), lower levels of alcohol consumption (except for younger men, who had a similar frequency of heavy drinking as their nondiabetic peers), similar levels of smoking, a higher prevalence of overweight, and significantly greater frequency of hospital admissions, use of outpatient services and general practitioner consultations. About half of the people with diabetes assessed their health as good or excellent but 90 per cent stated that they were happy or very happy. No differences between diabetic people living in capital cities and other areas were found. These results have implications for education and life‐style behaviour modification programs for people with diabetes. Research into the prevention and more effective management of diabetes and its complications is required in order to contain the escalating health care burden associated with diabetes in Australia.

Serum insulin is a risk marker for coronary heart disease mortality in men but not in women.

Serum insulin 1 h post-glucose load is examined in this prospective study of 2971 Caucasoid subjects aged > 20 years in 1966 and followed to 1989. The serum insulin levels as a continuous variable show no significant linear association with coronary heart disease (CHD) deaths in either sex after accounting for age by Cox proportional hazards analysis. In males the quintile classes of serum insulin show a striking U-shaped pattern with both the highest and lowest quintiles having significant associations with CHD deaths. In females the insulin quintiles show no direct association. Analysis for interactions of risk variables indicate that in females the relative protection of low cholesterol levels is abolished by hyperinsulinaemia after 12 years. Thus, serum insulin is not a direct aetiological risk factor for CHD. The findings suggest that the associations are likely to be due to confounding effects of unmeasured variables including lipid subfractions.

Obesity as Assessed by Body Adiposity Index and Multivariable Cardiovascular Disease Risk

To assess the role of body adiposity index (BAI) in predicting cardiovascular disease (CVD) and coronary heart disease (CHD) mortality, in comparison with body mass index (BMI), waist circumference (WC), and the waist circumference to hip circumference ratio (WHR). This study was a prospective 15 year mortality follow-up of 4175 Australian males, free of heart disease, diabetes and stroke. The Framingham Risk Scores (FRS) for CHD and CVD death were calculated at baseline for all subjects. Multivariable logistic regression was used to assess the effects of the measures of obesity on CVD and CHD mortality, before adjustment and after adjustment for FRS. The predictive ability of BAI, though present in the unadjusted analyses, was generally not significant after adjustment for age and FRS for both CVD and CHD mortality. BMI behaved similarly to BAI in that its predictive ability was generally not significant after adjustments. Both WC and WHR were significant predictors of CVD and CHD mortality and remained significant after adjustment for covariates. BAI appeared to be of potential interest as a measure of % body fat and of obesity, but was ineffective in predicting CVD and CHD.

Recreational physical activity as an independent predictor of multivariable cardiovascular disease risk.

The role of physical activity in preventing CVD has been highlighted by Professor Jerry Morris in the 1950’s. We report outcome of a 15-year prospective study with the aim to identify whether physical activity showed cardiovascular benefit independent of common risk factors and of central obesity. Baseline data of 8662 subjects, with no previous history of heart disease, diabetes or stroke, were obtained from an age- and gender- stratified sample of adults in Australian capital cities and were linked with the National Death Index to determine the causes of death of 610 subjects who had died to 31 December 2004. The study consisted of 4175 males (age 42.3±13.1 years) and 4487 females (age 42.8±13.2 years). Fasting serum lipid levels, systolic and diastolic blood pressure and smoking habits at baseline were recorded. The Framingham Risk Scores of 15-year mortality due to CHD and CVD were calculated using established equations. Subjects were also asked if they engaged in vigorous exercise, less vigorous exercise or walk for recreation and exercise in the past 2 weeks. Subjects in the high recreational physical activity category were 0.16 (0.06–0.43; p<0.001) and 0.12 (0.03–0.48; pu200a=u200a0.003) times as likely as subjects in the low category for CVD and CHD mortality respectively. After adjusting for both the Framingham Risk Score and central obesity (Waist circumference to Hip circumference Ratio), those in the high recreational physical activity group were 0.35 (0.13–0.98) times less likely compared to the low category for CVD mortality. Recreational physical activity independently predicted reduced cardiovascular mortality over fifteen years. A public health focus on increased physical activity and preventing obesity is required to reduce the risk of CVD and CHD.

Ethnicity and the association between anthropometric indices of obesity and cardiovascular risk in women: a cross-sectional study

Objectives The objectives of this study were to determine whether the cross-sectional associations between anthropometric obesity measures, body mass index (BMI), waist circumference (WC) and waist-to-hip ratio (WHR), and calculated 10-year cardiovascular disease (CVD) risk using the Framingham and general CVD risk score models, are the same for women of Australian, UK and Ireland, North European, South European and Asian descent. This study would investigate which anthropometric obesity measure is most predictive at identifying women at increased CVD risk in each ethnic group. Design Cross-sectional data from the National Heart Foundation Risk Factor Prevalence Study. Setting Population-based survey in Australia. Participants 4354 women aged 20–69u2005years with no history of heart disease, diabetes or stroke. Most participants were of Australian, UK and Ireland, North European, South European or Asian descent (97%). Outcome measures Anthropometric obesity measures that demonstrated stronger predictive ability of identifying women at increased CVD risk and likelihood of being above the promulgated treatment thresholds of various risk score models. Results Central obesity measures, WC and WHR, were better predictors of cardiovascular risk. WHR reported a stronger predictive ability than WC and BMI in Caucasian women. In Northern European women, BMI was a better indicator of risk using the general CVD (10% threshold) and Framingham (20% threshold) risk score models. WC was the most predictive of cardiovascular risk among Asian women. Conclusions Ethnicity should be incorporated into CVD assessment. The same anthropometric obesity measure cannot be used across all ethnic groups. Ethnic-specific CVD prevention and treatment strategies need to be further developed.

Independent external validation of cardiovascular disease mortality in women utilising Framingham and SCORE risk models: a mortality follow-up study

BackgroundWe conducted an independent external validation of three cardiovascular risk score models (Framingham risk score model and SCORE risk charts developed for low-risk regions and high-risk regions in Europe) on a prospective cohort of 4487 Australian women with no previous history of heart disease, diabetes or stroke. External validation is an important step to evaluate the performance of risk score models using discrimination and calibration measures to ensure their applicability beyond the settings in which they were developed.MethodsTen year mortality follow-up of 4487 Australian adult women from the National Heart Foundation third Risk Factor Prevalence Study with no baseline history of heart disease, diabetes or stroke. The 10-year risk of cardiovascular mortality was calculated using the Framingham and SCORE models and the predictive accuracy of the three risk score models were assessed using both discrimination and calibration.ResultsThe discriminative ability of the Framingham and SCORE models were good (area under the curveu2009>u20090.85). Although all models overestimated the number of cardiovascular deaths by greater than 15%, the Hosmer-Lemeshow test indicated that the Framingham and SCORE-Low models were calibrated and hence suitable for predicting the 10-year cardiovascular mortality risk in this Australian population. An assessment of the treatment thresholds for each of the three models in identifying participants recommended for treatment were found to be inadequate, with low sensitivity and high specificity resulting from the high recommended thresholds. Lower treatment thresholds of 8.7% for the Framingham model, 0.8% for the SCORE-Low model and 1.3% for the SCORE-High model were identified for each model using the Youden index, at greater than 78% sensitivity and 80% specificity.ConclusionsFramingham risk score model and SCORE risk chart for low-risk regions are recommended for use in the Australian women population for predicting the 10-year cardiovascular mortality risk. These models demonstrate good discrimination and calibration performance. Lower treatment thresholds are proposed for better identification of individuals for treatment.