Monday May 11 2015
Overweight diabetics tend to live longer than slimmer ones
“Overweight diabetics are 13 per cent less likely to die prematurely than those of a normal weight or those who are obese,” the Mail Online reports.
A new study followed over 10,000 English older adults with type 2 diabetes for 10 years. It examined how their body mass index (BMI) was linked to risk of later cardiovascular disease events such as heart attack and stroke, and death from any cause.
It found that overweight people had a 13% reduced risk of death compared with people who had a normal BMI. Risk of death was no different between obese people and those with a normal BMI.
However, it also found that people who were overweight or obese had an increased risk of cardiovascular disease events that required hospitalisation.
Great care must be taken before jumping to the conclusion that being overweight could be good for people with type 2 diabetes. As seen in this study, being overweight or obese increased the risk of diabetes complications, which could have an adverse impact on quality of life, even if not fatal.
The findings could also have been influenced by various factors other than BMI, including how well people’s diabetes is controlled. Further study is needed to uncover the biological mechanism, if there is a real link.
Current advice remains the same – whatever your current health, aim for a healthy BMI through a balanced diet and regular exercise.
Where did the story come from?
The study was carried out by researchers from University of Hull, Imperial College London and Federico II University in Naples, Italy. Financial support was provided by National Institute for Health Research, Hull York Medical School at the University of Hull, and Imperial College London.
The study was published in the peer-reviewed journal Annals of Internal Medicine.
The Mail’s coverage takes the findings at face value, suggesting that being overweight or obese could prolong life for people with type 2 diabetes. However, the study does not prove this and there are known adverse health risks of being overweight or obese.
What kind of research was this?
This was a prospective cohort study that aimed to investigate whether body weight has an influence on prognosis (what happens to health over time) in people with type 2 diabetes.
The link between obesity and increased risk of cardiovascular disease is well established. However, some other studies have suggested that in people with established cardiovascular disease, obesity could somehow offer a survival advantage. This observation has been named the "obesity paradox" – as it goes against what one would expect. The researchers wanted to investigate whether a similar link might be seen between obesity and survival in people with type 2 diabetes. The main limitation of this type of study is that there may be unmeasured confounding factors influencing any apparent relationship.
What did the research involve?
The study included adults diagnosed with type 2 diabetes who attended the outpatient clinic of a single NHS hospital in England, with a follow-up period of around 10 years. The researchers analysed whether participants’ BMIs were linked to their risk of cardiovascular events or death from any cause.
The participants had attended the clinic between 1995 and 2005, and had their data entered into a patient registry. A total of 10,568 people with type 2 diabetes (54% men) were included.
At the first visit data was collected on age, duration of diabetes, height, weight, blood pressure, smoking history and other significant illnesses (eg cancer, lung or kidney disease). All of these factors were adjusted for in analyses, to try to remove their effects.
Participants were followed for an average of 10.6 years, to end-2011. The main outcome examined was all-cause mortality (death from any cause). Cardiovascular events, such as heart attack, stroke or heart failure, were also examined.
What were the basic results?
Average BMI at the study's start was 29, which is in the overweight range, and participants had an average [median] age of 63 years.
During follow-up, 35% of participants died, 9% had a heart attack, 7% a stroke and 6% had heart failure. Overweight or obese participants (BMI >25) had a significantly higher risk of heart attack or heart failure than people of normal BMI (18.5 to 24.9). Risk of stroke was significantly increased in obese people (BMI >30), but not those who were overweight.
However, all-cause mortality risk was not increased for people who were overweight or obese.
Obese people had no significant difference in mortality risk compared with people with a normal BMI. Meanwhile, overweight people actually had decreased mortality risk compared with people with a normal BMI (hazard ratio (HR) 0.87, 95% confidence interval (CI) 0.79 to 0.95).
Meanwhile, underweight people had increased mortality risk compared with people with a normal BMI (HR 2.84, 95% CI 1.97 to 4.10), though there was no difference in their risk of cardiovascular disease events.
How did the researchers interpret the results?
The researchers conclude: "In this cohort, patients with type 2 diabetes who were overweight or obese were more likely to be hospitalised for cardiovascular reasons. Being overweight was associated with a lower mortality risk, but being obese was not."
This large prospective cohort following over 10,000 older adults with type 2 diabetes for 10 years has found that while being overweight or obese is linked to increased risk of cardiovascular events, being overweight is linked to reduced risk of death. This is similar to the "obesity paradox" seen in some other studies, where being overweight or obese is associated with a survival benefit in people with established cardiovascular disease.
The researchers note that 16 other studies have assessed the same question and found conflicting results. Their study aimed to improve on the methods in these studies, and its large sample size and prospective design, following people for 10 years, are strengths. However, caution must be taken before concluding from the findings of this cohort that "being FAT", as Mail Online states, is a good thing for people with type 2 diabetes.
There are important points to note:
- The cohort demonstrated significantly increased risk of cardiovascular disease events, such as heart attack and heart failure, for overweight or obese people with type 2 diabetes compared to healthy weight individuals. This is consistent with what is already known about the risks of overweight and obesity for cardiovascular disease.
- The researchers adjusted their analyses for various factors, including age, blood pressure, other illnesses and smoking history. However, other unmeasured confounding factors (confounders) could still be influencing the association between mortality and BMI – for example, other lifestyle factors (exercise, diet and alcohol) or health (including mental health), disability and quality of life factors. We also don’t know about diabetes medications each person was taking or how well controlled their diabetes was. If these factors differed between people with different BMIs, these could be influencing results rather than BMI itself.
- The study has also only looked at BMI but not at other measures of body fat, such as distribution of fat mass, or body weight in terms of fat mass and non-fat mass. Analysing these measures might be a way to confirm whether the BMI findings seem robust.
- As the researchers say, they have not specifically examined cause of death. An analysis of causes of death might help to understand why this difference is seen, and whether being overweight is having some protective effect.
- The study has looked at cardiovascular diseases and mortality only; the researchers have not looked at the development of other overweight- and obesity-linked diseases that may have had a detrimental effect on health.
- Though a large sample size, this is still a sample of older people with diabetes from a single UK region. Different results may have been obtained from other, more diverse, samples.
The reasons behind the apparent link are not yet known, and further study is needed into the possible biological mechanism. This study does not prove that being overweight is having a direct beneficial effect on risk of death in people with type 2 diabetes. The authors themselves caution against "promoting preconceptions about the ideal BMI" until further research is done to untangle the "obesity paradox".
For now, the advice regarding weight remains the same – whatever your current state of health, aim for a healthy BMI through a balanced diet and regular exercise.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.