Wednesday July 8 2015
A poor diet can increase the risk of a range of chronic diseases
"Suffering from heart disease, stroke and type two diabetes could knock 23 years off life," The Daily Telegraph reports, covering the stark conclusion of a major new UK study. The good news is many chronic diseases, such as stroke, are preventable.
As The Guardian reports, having a history of both heart attack and type 2 diabetes – increasingly common chronic conditions – can shorten life by around a decade.
Researchers looked at more than 130,000 deaths over 50 years. They then estimated the life-shortening effects of different diseases alone and in combination, and found these big three conditions significantly shortened lifespan.
The researchers used a large group and long timespan to make their estimates, giving us confidence in their main conclusions. But they are based on averages.
Each person's risks and lifespan is individual, and it is never too late to improve your health, even if you do have one or more chronic conditions: you can work towards maintaining a healthy weight, exercising more, eating healthily, not smoking, and not drinking too much alcohol.
Where did the story come from?
The study was carried out by researchers from the Emerging Risk Factors Collaboration co-ordinated by the University of Cambridge.
It was funded by the UK Medical Research Council, the British Heart Foundation, the British Heart Foundation Cambridge Cardiovascular Centre of Excellence, the UK National Institute for Health Research Cambridge Biomedical Research Centre, the European Research Council, and the European Commission Framework Programme 7.
A number of study authors declared potential financial conflicts of interest relating to funding from pharmaceutical companies, health trust funds and not-for-profit research organisations.
The study was published in the peer-reviewed Journal of the American Medical Association (JAMA).
Both The Guardian and The Daily Telegraph reported the main findings accurately, although neither discussed any limitations. Limitations are important to remind the reader no study is perfect or completely accurate.
The first line of The Telegraph's story told readers the diseases behind the 23-year life loss are largely preventable for "8 out of 10 people". This figure doesn't appear to have been taken from the main study publication, so we can't confirm whether or not this is accurate.
The Telegraph also used the term "heart disease", but the researchers specifically looked at people who had a heart attack (myocardial infarction). While a heart attack can be a common complication of heart disease, not everyone with heart disease will have one.
Nonetheless, it is well known you can reduce your risk of these conditions by living healthily, so there is something you can do about it.
What kind of research was this?
This analysis of two large cohort studies looked at the impact of diabetes, stroke and heart attack on life expectancy.
The researchers say more and more people are living with one or more conditions that increase their chances of dying early. The conditions of interest were heart attack, stroke and type two diabetes.
The researchers wanted to know the impact on lifespan of having more than one of these three conditions, looking at a large group of people over a significant amount of time.
To do this, they analysed some large and long-term cohort data sets. This is one of the most effective ways of estimating the impact of lifestyle on death across large groups.
The estimates rely on accurate estimates of lifestyle, usually reported in surveys, as well as having a lot of people in the group to boost reliability and generalisablity.
Such analysis produces averages – what happens to most people most of the time. While very useful, individual risk profiles vary from person to person, and can vary a lot around the average.
What did the research involve?
The research team analysed two large cohort studies, both of which had rich sources of lifestyle and medical information, allowing them to estimate the impact of different lifestyles and diseases on life expectancy.
The first and largest cohort was from the Emerging Risk Factors Collaboration. This had 689,300 participants from 91 cohorts, covering around 50 years of survey data from 1960-2007. This collected information on 128,843 deaths up to April 2013. The average age was 53, and most participants were from Europe (69%) or North America (24%).
The second cohort was from the UK Biobank. It was a little smaller, but more relevant to the UK. It had data on 499,808 participants with survey-derived lifestyle information spanning from 2006-10. Data on 7,995 deaths was gathered, the latest from November 2013. The average age was 57, and all from the UK.
Death rates were calculated for those with a history of two or more of the following:
- diabetes mellitus
- heart attack
The impact on lifespan of having each of the three conditions at different ages, alone or in combination, was estimated independently in both cohorts and then compared.
What were the basic results?
In men aged 60, a history of any two of the three conditions was associated with a 12-year lower life expectancy. A history of all three of these conditions was associated with 15 years of reduced life expectancy. The estimates were similar for women: 13 years lost for two conditions and 16 years for three.
Life lost was greatest if the history of the conditions was present earlier in life. Estimates in this study started at 40 and ran through until 95.
The highest estimate of life loss was 23 years, the figure picked up by The Telegraph. This related to men aged 40 with a history of diabetes, stroke and heart attack. The loss was only slightly lower in women with the same age and conditions, at 20 years.
Broadly speaking, the impact on risk of death from the three conditions was similar in both cohorts. The researchers found risk of death doubled with one condition, was four times as high with two conditions, and eight times higher with all three. This showed the risk effects were piling on top of each other in an exponential manner, rather than overlapping.
How did the researchers interpret the results?
The authors made three main interpretations. First, because of the addition nature of the results, they concluded that, "Our results emphasise the importance of measures to prevent cardiovascular disease in people who already have diabetes, and, conversely, to avert diabetes in people who already have cardiovascular disease."
Second, they said the shortening of life as a result of the three conditions studied was "of similar magnitude to those previously noted for exposures of major concern to public health, such as lifelong smoking (10 years of reduced life expectancy) and infection with the human immunodeficiency virus [HIV] (11 years of reduced life expectancy)."
Finally, they said there were important differences between men and women. "For men, the association between baseline cardiovascular disease (i.e. a history of stroke or MI) and reduced survival was stronger than for women, whereas the association between baseline diabetes and reduced survival was stronger for women."
This study used two large cohort-derived data sets to estimate the number of years of life lost as the result of a history of heart attack, stroke or diabetes across different ages.
The study's large size, relevance to the UK and long-term follow-up increases our confidence in its conclusions and their relevance to England and Wales. As with all studies, it has limitations, but these were relatively small and unlikely to affect the main conclusions.
This study shows a history of stroke, type 2 diabetes and heart attack can significantly shorten life expectancy, especially if these conditions are developed earlier in life, at around the age of 40.
But the good news is this is preventable – you can act now to minimise your risk of developing each of these conditions by maintaining a healthy weight, taking more exercise, eating healthily, stopping smoking, and not drinking too much alcohol.
Find out how you can reduce your risk of developing type 2 diabetes or having a heart attack or stroke.