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Complications of obesity

Understanding complications of obesity

Obesity is much more than just excess weight. It is associated with over 200 complications affecting an individual's health and various organ systems.1-8

Obesity also has a significant association with morbidity and mortality.9,10 Severe obesity has been associated with a decreased life expectancy and increased rate of death independent of age, geographic region, educational qualification or smoking.This includes a greater risk of developing diabetes, hypertension and hyperlipidaemia.10,11 Heart failure,12 metabolic syndrome13 and ischaemic stroke14 are other significant and well-evidenced complications of obesity. Obesity also increases mortality from a number of cancers, for example, breast cancer and prostate cancer.10 Similarly, individuals with obesity are at greater risk of mental health problems and overall decreased quality of life.15

The high rate of obesity complications emphasises how important early intervention is in order to prevent serious outcomes.

Click on any of the complications below for more information on their association with obesity and the impact of health.


Cardiovascular disease – hypertension, dyslipidaemia and heart failure

Association with obesity

Cardiovascular disease is the leading cause of mortality in people with obesity.16 There is clear association between BMI, hypertension (high blood pressure) and heart failure. For example, the prevalence of hypertension increases with increasing BMI, 17 whereby people with a BMI of 25.0–29.9 kg/m2  are three times more likely to develop hypertension than individuals with a normal range BMI.17 With higher BMI, the risk of hypertension increases, even among individuals within the “normal” and mildly “overweight” BMI range.17 Amongst those with a normal BMI, there is a 45% prevalence of hypertension compared to 67% for those who are overweight, 79% for those in obesity class I and II and then up to 87% amongst those in obesity class III.18 Obesity is also associated with dyslipidaemia with approximately 60-70% of patients living with obesity also having dyslipidaemia.19

Not only is obesity one of the most common comorbidities of heart failure with preserved ejection fraction (HFpEF) but also one of the major risk factors for its development.20 Additionally, there is a significant association between ischaemic stroke and obesity.21

Weight loss impact on health

For people with obesity and stage 1 hypertension, recommendation is to treat patients by reducing weight through lifestyle modifications, pharmacological treatment and/or bariatric surgery.22 These findings indicate that weight loss is important for the prevention, as well as the initial treatment, of hypertension.


Pre-diabetes and type 2 diabetes

Association with obesity

Men and women living with obesity are almost 7 and >12  times more likely to develop type 2 diabetes than individuals without obesity respectively.10

In fact, one of the long-term side effects of obesity is that it is the leading risk factor for type 2 diabetes.23 The American Diabetes Association recommends that physicians test for diabetes and assess risk in asymptomatic individuals over the age of 45 simply if they are overweight or obese; additionally, they should test regardless of age if patients are severely obese.24 Living with overweight or obesity increases the risk of developing type 2 diabetes by a factor of three and seven respectively.24

Weight loss impact on health

For individuals with pre-diabetes, weight loss not only reduces the risk of developing type 2 diabetes2  but can also take type 2 diabetes into remission.25 Weight loss studies show that over an average follow-up period of 2.8 years, the risk of developing type 2 diabetes can be reduced.2  Importantly, in patients with obesity and pre-diabetes, even  10 years  after initial weight loss, and despite weight regain, there is a significant reduction in the risk of developing type 2 diabetes compared to those individuals who didn’t lose any weight.26 Similarly, weight loss studies after bariatric surgery found that individuals had lower 2- and 10-year incidence rates of type 2 diabetes following weight loss surgery.27



Association with obesity

Men and women with obesity are >2 and 2 times  more likely to develop osteoarthritis than someone without obesity, respectively.10

Every 5 kg of weight gain confers a 36% increase in the risk of knee osteoarthritis.28 High BMI throughout adulthood increases that risk, with the association between BMI and later life knee osteoarthritis beginning as early as 20 years in men and 11 years in women.28

Interestingly, a raised BMI during the ages of 20-29 predicts a risk of later knee osteoarthritis better than current weight, suggesting obesity is one of the major causes of osteoarthritis rather than inactivity secondary due to knee decay.29

Weight loss impact on health

Weight loss – through diet and physical activity – is the first recommendation in any guideline for knee osteoarthritis.30

Research has shown that, amongst patients with overweight and obesity affected by knee osteoarthritis, every pound of weight lost resulted in a fourfold reduction in the load exerted on the knee per step during daily activities.28

Studies suggest that if people with overweight and obesity reduced their  weight by 5 kg or until their BMI was within the recommended normal range, 24% of surgical cases of knee osteoarthritis might be avoided.5  In these cases, weight loss is recommended as part of management and also leads to symptom relief and improves functional status and reduces pain.6


Polycystic ovary syndrome (PCOS) and infertility

Association with obesity

The pathophysiology of polycystic ovary syndrome (PCOS) is complex and remains largely unclear, however the condition has been found to be intricately linked with obesity. Studies show that up to 76% of women with PCOS have obesity. Obesity is considered to contribute and exacerbate complications of PCOS,31 including the development of insulin resistance and pre-diabetes/type 2 diabetes,32 cardiovascular disease,33 and fertility problems or infertility.32

The rising obesity epidemic suggests that this prevalence may rise in the future.34

Another common side effect of obesity amongst women are menstrual irregularities.29 In one study, where 32.3% of women who were living with obesity suffered from menstrual irregularities, a weight reduction of 7-8 kg through diet and exercise improved menstrual regularity in 80% of the women who lost weight.35

Weight loss impact on health

Weight loss is the primary recommendation for PCOS,35 improving clinical features and long-term metabolic health in women with PCOS. Some of these improvements include lowered insulin levels,36 decreased insulin resistance,32 decreased androgen levels and risk factors for cardiovascular disease and type 2 diabetes.33 Importantly, menstrual cyclicity, ovulation and fertility37 have been shown to improve following weight loss.32

Amongst women with PCOS, the reduction in insulin is thought to be the main determinant of most reproductive weight loss benefits.34


Sleep apnoea and asthma

Association with obesity

Approximately 40% of people with obesity are thought to have obstructive sleep apnoea.38

One of the consequences of obesity is that the fat deposition on the neck, chest wall and abdomen has adverse effects on lung function, reduced chest wall and diaphragm movement and lung volumes,29 causing shortness of breath and hypoventilation.39 Whilst awake and upright, these impacts are usually small but lying flat exacerbates them, causing the prevalence of sleep apnoea.29

Asthma is another common respiratory disease that has been linked with obesity health risks.40 There is a 92% increase in risk of asthma when BMI exceeds 30 kg/m2.40

Weight loss impact on health

Losing weight may help people with obesity sleep better by easing obstructive sleep apnoea symptoms. Studies suggest that 7-11% weight loss may decrease apnoea and hypopnoea index in individuals.41

Bariatric surgery and low-calorie diets positively impact bronchial hyper-responsiveness and airway inflammation, as well as clinical outcomes in obese patients, pointing towards a functional link between asthma and obesity.40

Linking obesity, BMI and risk of mortality

The adverse consequences of obesity, obesity-related diseases and issues around obesity, across all areas of health, mean that the condition also decreases lifespan.42


Research shows that a high BMI is associated with a decreased life expectancy of up to 10 years.43  For every 5 kg/m2  BMI increment above the range of 22.5–25.0 kg/m2, there is a 30% increase in overall mortality.43

Adapted from Prospective Studies Collaboration. Body-mass index and cause-specific mortality in 900,000 adults: collaborative analyses of 57 prospective studies. Lancet. 2009;373(9669):1083–1096.


Conditions caused by obesity and their determinants are complex, leading to numerous comorbidities and medical complications. But advances in healthcare have provided us with a range of tools and ways to better manage obesity. 

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