A fifth of Australians will battle at least two chronic diseases in their lives, with arthritis and cardiovascular disease the most frequent

A fifth of Australians are affected by multiple chronic diseases, data released by the Australian Institute of Health and Welfare shows.

The data - which is aimed at informing health policy - covers eight chronic diseases: arthritis, asthma, back problems, cancer, chronic obstructive pulmonary disease, cardiovascular disease, diabetes and mental health conditions.

About half of all Australians are battling a chronic disease, while one in five have at least two, the data shows.

Ageing is a factor that has a strong association with `comorbidity' - when two or more diseases occur at the same time.

Nearly 40 per cent of Australians aged 45 and over have two or more of the eight chronic diseases.

Arthritis and cardiovascular disease occurred together most frequently, in 16 per cent of the population, followed by arthritis and back problems (10 per cent) and back problems and cardiovascular disease (eight per cent).

"Sometimes these diseases occur together simply by chance, but often it's because there are some associations between them, such as shared risk factors," AIHW spokesperson Louise York said in a statement.

"Older people are more vulnerable to developing many diseases, and Australians' increasing life expectancy means a greater chance for multiple conditions to arise."

Among those aged 0-44, mental health conditions and back problems were the most common, followed by mental health and asthma, and back problems and asthma.