Heart disease and stroke mortality rates have almost stopped declining in many high-income countries, including Australia, and are even increasing in some countries, according to new research.

University of Melbourne researchers have analysed trends in cardiovascular disease mortality -- which consists of mainly heart disease and stroke -- in 23 high-income countries since the year 2000.

Researchers found cardiovascular disease mortality rates for people aged 35 to 74-years-old are now barely declining, or are increasing, in 12 of the 23 countries.

In the USA and for Canadian females, cardiovascular disease mortality rates have increased in the most recent year, while in Australia, the United Kingdom and New Zealand annual declines in deaths from cardiovascular disease are now only 20 to 50 per cent of what they were in the 2000s.

University of Melbourne expert on the global burden of disease Alan Lopez said research suggests that obesity, or at least poor diet, may have been a significant contributor to the slowdown in the decline of cardiovascular disease deaths.

"Each of these countries have very high levels of obesity. In Australia, close to one-third of adults are obese," Professor Lopez said.

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"These increases in obesity levels mean that a significant portion of the population has been exposed to the cardiovascular disease risks associated with being overweight for several decades."

However, obesity is only one of many risk factors for cardiovascular disease mortality -- others include smoking, high blood pressure, high cholesterol and diabetes.

Researchers found obesity levels are low in Italy and France where the slowdown in cardiovascular disease mortality in recent years is among the most notable of all countries.

University of Melbourne researcher and co-author Tim Adair said the research shows that the effect of successful public health interventions on cardiovascular disease mortality over the past 50 years is diminishing.

"In order to combat this, significant investment in preventive health measures is needed, particularly those aimed at increasing physical activity, improving diet and reducing obesity," Dr Adair said.

"Failure to address these issues could confirm the end of the long-term decline in cardiovascular disease deaths and threaten future gains in life expectancy."

This research is published in the International Journal of Epidemiology.