What are the risk factors for multimorbidity?

While the number of chronic conditions a person has tends to increase with age, more often than not, conditions occur together because there is some association between them. A number of chronic conditions share common risk factors, or one disease may be a risk factor in itself for another (AIHW 2016a). Diabetes is a well-known risk factor for cardiovascular disease, possibly due to diabetes increasing atherosclerosis (thickening of blood vessel walls with plaque deposits), which is the underlying cause of most cardiovascular disease in Australia (Woo et al. 2008).

At the individual level, a number of biomedical and behavioural risk factors can affect the likelihood of developing chronic conditions (AIHW 2016b). Biomedical characteristics that contribute to the development of chronic conditions include overweight and obesity, high blood pressure, dyslipidaemia (high blood cholesterol) and a person’s genetic make-up. Biomedical risk factors are often influenced by behavioural risk factors. Behavioural risk factors include physical inactivity, poor nutrition, smoking tobacco and risky alcohol consumption. As with chronic conditions, many of these behavioural risk factors tend to be more prevalent in the lowest socioeconomic areas and in regional and remote areas (AIHW 2020a, AIHW 2020b).

The relationship between behavioural risk factors and multimorbidity is complex. Research based on data collected at a single point in time has found that the more chronic conditions a person reports, the more risk factors they are likely to have (AIHW 2012). However, without information on exposure to risk factors over time and the timing of chronic condition onset, the presence of chronic conditions cannot be attributed to the number of risk factors a person has. This is because the onset of some chronic conditions may motivate a person to change their behaviour for the better. For example, a diagnosis of COPD may motivate a person to quit smoking. In contrast, the onset of a chronic condition may result in an individual being less able to participate in physical activity.

Longitudinal research can help to understand the interacting complexities of risk factors and multimorbidity. A study of multimorbidity in Australian women has shown overweight and obesity, physical inactivity and social inequality to be risk factors common to a number of patterns of multimorbidity (Jackson et al. 2016).

At the societal level, the availability of health services, vaccination programs and a clean and healthy environment can promote good health and reduce the risk of developing, or exacerbating existing, chronic conditions. Aspects of the natural and built environment, including the availability of healthy food, building design, access to green space, exposure to advertising, portion sizes of prepared food and the convenience of pre-packaged, calorie dense food also contribute to overweight and obesity (AIHW 2017), which are risk factors for the development of chronic conditions.

Many of the individual and societal risk factors for chronic conditions are largely modifiable or treatable (AIHW 2016). Changes in behaviour, together with timely and effective medical treatments, can reduce the risk of developing chronic conditions, and multimorbidity, resulting in large population health gains.