Being cynical can increase the risk of heart disease, US researchers claim.

A study of 6,814 people found that cynical distrust was associated with signs of inflammation which in turn increase the risk of heart disease.

Chronic stress and depression were also found to be associated with higher levels of certain inflammatory markers in the blood.

The Archives of Internal Medicine study suggests cynical people are more likely to lead unhealthy lifestyles.

Researchers from the University of Michigan asked participants to fill out a questionnaire that assessed a person's risk of chronic stress or depression.

Cynical distrust was measured at a later follow-up visit.

They also took blood samples from participants who were aged between 45 ane 84 years.

The samples were analysed for three markers of inflammation - fibrinogen, C-reactive protein, and IL-6.

Higher levels of cynical distrust were associated with higher levels of all three inflammatory markers.

Chronic stress was linked with higher levels of IL-6 and C-reactive protein and depression was associated with higher levels of IL-6.

"The strongest and most consistent associations were observed for cynical distrust, which was positively associated with all three inflammatory markers," said study leader Dr Nalini Ranjit.

Inflammation

Previous studies have reported links between psychosocial factors such as stress and cardiovascular disease.

However, the reason for this is unclear.

Inflammation is an important pathway in the development of atherosclerosis - a process where the arteries become narrow and hardened blocking blood flow - and in heart attacks and strokes.

When Dr Ranjit and colleagues analysed the findings in more detail they found that much of the increase in inflammatory markers was linked to unhealthy lifestyle factors, such as obesity and smoking.

They concluded that cynical people might be more likely to indulge in unhealthy behaviour, and that it was this that could explain their higher risk of heart disease.

Vicky Styman, a cardiac nurse at the British Heart Foundation, said there was insufficient evidence to say that emotion was a significant risk factor for heart disease.

She said: "One difficulty is that emotions are subjective. Some people thrive on stress while others prefer a slower pace, and it is often how people deal with stress that can increase their risk of heart disease rather than the stress itself.

"It is particularly difficult to define if someone is cynical and measure what impact this has on their likelihood to develop disease.

"As the authors of this study acknowledge, psychological factors such as stress can often lead to unhealthy behaviours, including smoking, eating an unhealthy diet and physical inactivity - all of which are established risk factors for heart disease."