Big problem: The decline in heart disease deaths for middle-aged Australians has slowed in recent years.

Big problem: The decline in heart disease deaths for middle-aged Australians has slowed in recent years.

Experts fear obesity, poor diet and lack of exercise may be the reason for a slowing decline in heart disease deaths for middle-aged Australians.

An Australian Institute of Health and Welfare report has found deaths from heart disease, Australia's biggest killer, are declining, but in recent years the falling rates have halved for people between the ages of 40 and 54.

The report, released on Thursday, reveals overall rates of heart disease deaths decreased more than 70 per cent between 1979 and 2010. The annual number of deaths was 21,700 in 2010 - down from 31,000 in 1979. 

Although heart disease death rates for people over the age of 70 continue to fall at a rate of about 5.1 per cent a year, the news is not as promising for younger Australians. 

The report found the average annual decrease in heart disease deaths for men aged 40-54 was 6.6 per cent between 1979 and 1993, but the decline more than halved between 2000 and 2010 to just 3.2 per cent. 

For women in the same age group, the average yearly decline fell to just 2.7 per cent between 1997 and 2010 compared to an average annual decrease of 7.4 per cent between 1979 to 1997. 

The report found declines in the death rate also slowed for people between the ages of 25 to 39 and 55 to 69. 

AIHW spokeswoman Sushma Mathur said it was believed trends, such as obesity, diet, diabetes and lack of exercise - all risk factors for heart disease - could be partly to blame for why the decline in heart disease deaths for middle-aged Australians had slowed in recent years. 

''We've seen an increase in the prevalence of obesity, we're seeing higher rates of physical inactivity and people not consuming adequate amounts of fruit and vegetables and I think all of this in turn, has led to an increase in the prevalence of diabetes and we are seeing diabetes occurring at younger ages and we know that is a key risk factor for the development of coronary heart disease,'' she said.

''If these trends in risk factors remain unchecked and with the ageing population, we are likely to see large increases in the development of coronary heart disease so we will continue to see the burden of heart disease increasing if we don't overcome the issues we have at the moment with obesity and diabetes.

''In the 40 to 54 age group, rates of decline have almost halved so that is a concern and I think further research is needed to really unpack that and see what the underlying factors are for that." 

Heart disease remains the leading cause of death in Australia with the report finding that about 15 per cent of all deaths in Australia were from heart disease in 2010 - down from about 29 per cent in 1979.

The report also looked at death rates for Aboriginal and Torres Straight Islander people, finding they had also improved, but they still remained higher in comparison to the mortality rates for other Australians.

''The good news from this report is that the decline in coronary heart disease for indigenous and non-indigenous people is the same so even though the gap is still large, we are now finding that the rate of improvement is similar,'' she said.

Ms Mathur said the report's findings underpinned the need for ongoing awareness around heart disease.

''I think the report shows that we should not get too complacent in terms of the large gains that have been made. There have been some enormous gains but at the same time, we also need to be mindful that there are certain age groups where we are starting to see a slowing in the decline of coronary heart disease mortality rates,'' she said.

Professor Rachel Davey, from the University of Canberra and Centre for Research and Action in Public Health director, said diet, obesity and physical inactivity were known risk factors for heart disease. 

She said there had also been advances in medication and treatment.