Everything that is biological is psychological, and everything that is psychological is biological. The brain and body are one. Lowering stress and improving your mental wellbeing can significantly improve your physical wellbeing and lower your chance of contracting illnesses and diseases. Another example of this was found recently by researchers in Norway who were studying the link between heart disease and health anxiety. Study participants were followed over a twelve-year period and monitored for factors such as health, lifestyle, and education levels. And their anxiety levels were also closely monitored. Based on the data, this study concluded that twice as many study participants who had health-related anxiety developed heart disease compared to those who did not have anxiety. Even after adjusting for other cardiovascular risk-factors people with health-related anxiety had a 73% increased risk of developing heart disease. You can read more about this study here.