"Obesity knocks 20 years of good health off your life and can accelerate death by eight years," the Mail Online reports.

A study has estimated very obese men aged 20 to 39, with a body mass index (BMI) of 35 or above, have a reduced life expectancy of eight years.

This is as a result of their higher risk of cardiovascular disease and type 2 diabetes. For women of this age, the life expectancy is six years less.

What is also worrying is the much larger number of healthy years of life lost because of the chronic illness caused by these two conditions, which are obesity related.

Obesity in this age group is estimated to cause 11 to 19 fewer years of healthy life, which could have a considerable negative impact on a person's quality of life.

This is likely to be an underestimate, however, as it did not take into account other illnesses associated with increased weight, such as certain cancers, liver and kidney diseases.

A truism is that a model is only as good as the data you put into it. Reassuringly, the researchers used a well-regarded data set.

The researchers hope these results can help healthcare professionals give people a greater understanding of how much obesity is putting people at risk of long-term chronic ill health.

Where did the story come from?

The study was carried out by researchers from the University Health Centre in Montreal, McGill University, the University of British Columbia and the University of Calgary.

It was funded by the Canadian Institutes of Health Research.

The study was published in the peer-reviewed medical journal The Lancet: Diabetes & Endocrinology.

The UK media's reporting was generally accurate, although some of the details were fudged. The Mail Online went with, "obesity knocks 20 years of good health off your life", which referred to the 18.8 and 19.1 years of life lost in very obese men and women respectively aged 20-39.

Other headlines tended to use an "eight years of life lost" figure. This referred to very obese men aged 20-39. The equivalent estimate was less for women (six years), older age groups, and for those who were overweight or obese.

What kind of research was this?

This was a modelling study to estimate how obesity affects life expectancy and the number of years of poor health that result from cardiovascular disease and type 2 diabetes.

Modelling studies are able to estimate events occurring over time in large samples of the population, which would otherwise take too many years and resources to collect. They are based on risk estimates and population data.

What did the research involve?

The researchers designed a computer model for predicting life outcomes from type 2 diabetes and cardiovascular disease, according to body mass index (BMI) and waist circumference.

A previous health model was used to predict the likelihood and outcomes of cardiovascular disease. The researchers combined this model with a new model for type 2 diabetes.

The researchers used data collected from the National Health and Nutrition Examination Survey (NHANES) to feed into the computer model. This is an ongoing cohort study, though the researchers used data from 2003-10.

They used information about adults from the US aged 20 to 79 years old. The information included BMI, gender, smoking status, blood pressure, fasting glucose and HDL cholesterol (so-called "good cholesterol").

The computer model then calculated the probability of each participant developing type 2 diabetes or cardiovascular disease each year.

The model took into account that similar risk factors increase the risk of both conditions (such as smoking) and each condition increases the risk of the other.

Once entered into the system, each year their health status could either:

stay the same

a new diagnosis could be made

existing disorders could cause complications or progress

the individual could die from type 2 diabetes, cardiovascular disease or another cause

The model went through many cycles and individuals remained in the system until death or they reached 102 years old.

The researchers then calculated the average life expectancy and healthy life expectancy free from diabetes or cardiovascular disease. They validated their results by comparing them with other models.

What were the basic results?

Healthy life years lost were two to four times higher than the total years of life lost for all age groups and body weight categories.

Very obese people consistently had the largest number of years lost and healthy years lost.

The largest life lost was in very obese women aged 20-39 years, at 19.1 years. Very obese men in the same category were the highest for healthy years lost, at 18.8 years.

The figures were consistently lower for those in the obese and overweight categories than the severely obese category.

Similarly, the years of life and years of healthy life lost estimates were generally much higher in the younger groups (20-39 years) than the older groups. This was not particularly surprising, as the risk is cumulative over a person's lifetime.

Healthy years lost compared with ideal body weight

The healthy years of life lost for obese men (BMI 30kg/m2 to less than 35kg/m2):

aged 20 to 39 was 11.8 years (95% confidence interval [CI] 9.9 to 13.7)

aged 60 to 70 was 3.9 years (95% CI 2.8 to 5.0)

The healthy years of life lost for very obese men (BMI 30kg/m2 to less than 35kg/m2):

aged 20 to 39 was 18.8 years (95% CI 16.8 to 20.8)

aged 60 to 70 was 3.9 years (95% CI 2.8 to 5.0)

The years of life lost for obese women (BMI 30kg/m2 to less than 35kg/m2):

aged 20 to 39 was 14.6 years (95% CI 12.0 to 17.2)

aged 60 to 79 was 6.3 years (95% CI 5.2 to 7.4)

The years of life lost for very obese women (BMI over 35 kg/m2):

aged 20 to 39 was 19.1 years (95% CI 16.7 to 21.5)

aged 60 to 79 was 7.3 (95% CI 6.1 to 8.5)

Life years lost compared with ideal body weight

The years of life lost for obese men (BMI 30kg/m2 to less than 35kg/m2):

aged 20 to 39 was 5.9 years (95% CI 4.4 to 7.4)

aged 60 to 79 was 0.8 years (95% CI 0.2 to 1.4)

The years of life lost for very obese men (BMI over 35 kg/m2):

aged 20 to 39 was 8.4 (95% CI 7.0 to 9.8)

aged 60 to 79 was 0.9 (95% CI 0 to 1.8)

The years of life lost for obese women (BMI 30kg/m2 to less than 35kg/m2):

aged 20 to 39 was 5.6 years (95% CI 4.1 to 7.1)

aged 60 to 79 was 1.6 years (95% CI 0.8 to 2.4)

The years of life lost for very obese women (BMI over 35 kg/m2):

aged 20 to 39 was 6.1 years (95% CI 4.6 to 7.6)

aged 60 to 79 was 0.9 (95% CI 0.1 to 1.7)

How did the researchers interpret the results?

The researchers concluded that, "When the effect of living with a chronic illness such as type 2 diabetes or cardiovascular disease is considered, healthy life years lost were two to four times greater than total years of life lost and, in some instances, as much as eight times greater."

Conclusion

This modelling study has shown estimates of the number of years of poor health associated with type 2 diabetes and cardiovascular disease is much higher than the number of years lost because of the conditions.

The researchers hope these results can help healthcare professionals give people a better understanding of how much obesity is putting people at risk of long-term chronic ill health.

The results of this model show the risks are greatest for younger people and increase with higher levels of obesity.

But there are some limitations to take into account when considering this study:

The participants were all of white ethnicity, so the results may not be applicable to people of different ethnic backgrounds, especially as diabetes prevalence can vary by ethnicity.

The model did not take into account other illnesses associated with increased weight, such as certain cancers, liver and kidney diseases, so may underestimate the number of life years and healthy years lost.

The results are estimates at a population level, and they should not be used to predict an individual's likely health or life outcomes.

This study highlights the pressing need for obesity to be tackled to reduce the years of likely chronic illness and premature death rates from type 2 diabetes and cardiovascular disease. There is no quick fix for obesity, but the first steps to weight loss can be found here.

Analysis by Bazian

Edited by NHS Website