Obesity and chronic disease

The 2011–13 Australian Health Survey results to date have highlighted the growing problem of obesity in Australia. It is estimated that 62.8% of Australian adults are now overweight or obese, with this figure increasing over the past two decades (up from 56.3% in 1995).¹

The first biomedical results from the National Health Measures Survey (NHMS) showed that being overweight or obese increased the risk of abnormal test results for nearly every chronic disease tested in the NHMS. These differences remained even after age was taken into account.

This article looks more closely at how obesity was associated with cardiovascular disease, diabetes and liver disease.

Results from the Australian Health Survey showed that 6.2% of all adults had current and long-term heart, stroke or vascular disease.¹ Most commonly this group of conditions is referred to under the broader term of 'heart disease' or 'cardiovascular disease'.

Cardiovascular disease remains one of the leading causes of death worldwide. In 2011, ischaemic heart disease, which includes angina, blocked arteries of the heart and heart attacks, was the leading cause of death for all Australians, representing 14.6% of all deaths registered in 2011.²

The main indicators of cardiovascular disease that were measured in the NHMS were cholesterol, including LDL and HDL cholesterol, and triglycerides. In 2011–12, around one in three Australian adults (32.8%) had high levels of total cholesterol, with around one in four (23.1%) having lower than normal levels of HDL 'good' cholesterol and one in three (33.2%) having high LDL 'bad' cholesterol. Around 14% had high triglycerides.

Taking all these tests into account, around 63.2% of people aged 18 years and over had dyslipidaemia. That is, they were taking cholesterol-lowering medication or had one or more of high total cholesterol, low HDL cholesterol, high LDL cholesterol or high triglyceride levels based on their test results. This comprised 13.8% who took cholesterol-lowering medication and 49.4% who took no medication but had at least one abnormal test result.

Research shows that excess body weight is a major risk factor for heart disease, as high levels of body fat can raise blood lipid levels which can cause fatty deposits developing in the arteries, increasing the risk of heart attack or stroke.³ In 2011–12, people who were obese were nearly five times as likely as those who were of normal weight or underweight to have high triglycerides (25.3% compared with 5.3%) and more than twice as likely to have lower than normal levels of HDL 'good' cholesterol (36.2% compared with 14.1%). This pattern was also evident for total cholesterol but the relationship was not as strong.

It is well documented that the risk of cardiovascular disease increases after the age of 45 years.⁴ However, the NHMS shows that a significant number of adults under 45 years had indicators of cardiovascular disease, especially among those who were obese. For example, four in every ten (39.1%) obese adults under the age of 45 years had lower than normal levels of HDL 'good' cholesterol and nearly one in four (22.6%) had high triglycerides. This was substantially higher than for those aged 18–44 years who were of normal weight or underweight (15.4% and 4.5% respectively). This was also higher than the equivalent rates for all people aged 45 years and over (22.5% for lower than normal HDL cholesterol and 16.7% for high triglycerides).

The risk of cardiovascular disease further increased when obesity was combined with smoking, particularly for younger people. Around half (51.7%) of those aged 18–44 years who were current daily smokers and obese had high LDL 'bad' cholesterol levels. This compared with only 15.8% of those who were both a non-smoker and of normal weight or underweight. Young smokers aged 18–44 years who were obese were also much more likely to have high triglycerides (27.0% compared with 3.7%) and abnormal levels of HDL 'good' cholesterol (52.3% compared with 14.8%).

Similarly, people aged over 45 years who smoked and who were obese were much more likely to have lower than normal HDL cholesterol (52.3%) and high triglycerides (36.8%) than people who did not smoke and who were of normal weight or underweight (10.8% and 5.9% respectively). However, the combination of smoking and obesity did not significantly increase rates of abnormal total cholesterol or LDL cholesterol for this age group.

According to the NHMS, 5.1% of Australians aged 18 years and over had diabetes. This comprised 4.2% with known diabetes and 0.9% whose test results indicated diabetes, but who were previously unaware that they had the condition. A further 3.1% of adults were identified as not currently having diabetes, but were at high risk of having the condition.

Obesity is a known risk factor for diabetes as excess body weight can interfere with the body's production of, and resistance to, insulin.⁵ In 2011–12, adults who were obese were seven times as likely as those who were of normal weight or underweight to have diabetes.

People who were obese were also more likely to be at high risk of diabetes. Around one in every twenty (5.8%) obese people who did not already have diabetes were at high risk of the condition, compared with less than 1% of those who were normal weight or underweight.

A range of factors, including fatty liver disease, infections and excessive alcohol consumption can prevent the liver from functioning properly.⁶ The NHMS included two tests for liver function: gamma glutamyl transferase (GGT) and alanine aminotransferase (ALT). These tests check the liver’s health and can detect liver damage.

In 2011–12, around one in ten (11.0%) people aged 18 years and over had abnormal levels of ALT in their blood and 12.4% had abnormal levels of GGT.

Excess body fat is recognised as a risk factor for liver disease.⁷ In 2011–12, people who were obese were around four times as likely than those who were of normal weight or underweight to have abnormal ALT levels (19.5% compared with 4.6%). Likewise, around one in five (21.6%) people who were obese had abnormal GGT compared with only 6.0% who were of normal weight or underweight.

Similarly to cardiovascular disease, young people who were obese were also at higher risk of liver disease. Among those aged 18–44 years, obese people were five times as likely as those of normal weight or underweight to have high ALT levels (24.9% compared with 4.6%) and nearly six times as likely to have high GGT levels (19.0% compared with 3.2%).

For more information on how Body Mass Index and other lifestyle risk factors are associated with biomedical test results, see table 8 in the Data downloads section in the topic page of this publication.