Medical School

Postgraduate research profiles

Chi Le-Ha

Thesis

The influence of gender and lifestyle on cardiovascular risk factors in late adolescence

Summary

Risk factors and risk behaviours that promote the development of atherosclerotic cardiovascular disease (CVD) begin early in life. Adolescence is a critical period in the developmental course of the natural history of CVD, because it is during this period that lifestyle and behaviours that may adversely affect long-term cardiovascular risk are adopted. Obesity, the use of oral contraceptives (OC) in females, and other lifestyle factors such as dietary patterns, salt intake, alcohol consumption, cigarette smoking and physical activity are known to influence blood pressure (BP) and CVD risk in adults. In addition, the harmful effects of passive smoking exposure and maternal smoking in pregnancy on cardiovascular risk later in life have been reported.

Although the influence of gender on CVD risk has been extensively studied, little is known about how gender interrelates with clinical, biochemical and behavioural risk factors in late adolescence. Adolescence is also a period of emotional development and brain plasticity, during which both lifestyle and neuroendocrine mechanisms can influence the development of cardio-metabolic disorders.

My thesis examined data from adolescents at 17 years of age in the Western Australian Pregnancy Cohort (Raine) Study, a population-based pregnancy cohort. I aimed to investigate (i) the relationship between lifestyle factors and BP at 17 years, with particular reference to sex differences and their interaction with adiposity; (ii) the effects of long-term passive smoking exposure since birth and maternal smoking during pregnancy on HDL-cholesterol (HDL-C) at 17 years; (iii) the influence of active smoking on high-sensitivity C-reactive protein (hs-CRP) at 17 years; and (iv) the link between basal hypothalamus-pituitary-adrenal (HPA) axis activity and cardiovascular risk factors at 17 years.

I have shown that boys had 8.97 mmHg higher systolic BP compared with girls. OC use in girls, alcohol consumption in boys, increasing body mass index (BMI) and the urinary sodium-potassium ratio were associated with higher systolic BP. I showed that there is a continuous relationship between BMI and systolic BP in both genders, but the relationship shows a steeper gradient in boys, compared with girls not using OCs.

HDL-C levels were significantly lower in girls exposed to passive smoking since birth, compared with girls not exposed to passive smoking. There was no association between passive smoking and HDL-C in boys. Unexpectedly, there was no evidence of an association with HDL-C in girls whose mother smoked in pregnancy and subsequently were exposed to passive smoking.

Active smoking at 17 years was associated with higher levels of hs-CRP in girls not using OCs, but not in girls using OCs, or in boys. OC use in non-smoking girls was the strongest factor associated with higher hs-CRP levels.

In this adolescent population, I observed significant associations between basal HPA axis activity and a range of conventional CVD risk factors. Specifically, basal HPA hyperactivity was associated with higher levels of systolic BP, total cholesterol, and hs-CRP.

In summary, I have demonstrated the associations between a number of behavioural and lifestyle factors, as well as altered neurobehavioural function through the stress systems, and an adverse CVD risk profile in adolescents at 17 years of age. These findings are important in the context that adolescence is a time when unhealthy lifestyle behaviours that influence long-term CVD risk tend to become entrenched, and also a time of critical development in emotional and neurobehavioural function that may impact cardio-metabolic risk.

Why my research is important

In view of the the importance of adolescence as a crucial time for prevention and early recognition of future cardiovascular disease, my thesis is an investigation of the most important biological and socio-behavioural factors that potentially influence long-term cardiovascular health risk in an Australian birth cohort at 17 years of age.

Funding

  • Endeavour Postgraduate Award, from the Australian Government;
  • Raine Study PhD Scholarship, The Raine Foundation.