This so-called "obesity paradox" might mean obesity is actually protective, or type 2 diabetes in older people is somehow different than it is in younger people, the researchers speculate.
Dr Joel Zonszein, the director of the clinical diabetes centre at the Montefiore medical centre in New York, said: "My feeling is that fat is not protective, but the ones who are dying have more bad fat and more aggressive diabetes."
"It's not just a matter of weight, but where the weight is and how aggressive the diabetes is that makes the difference."
"What we are seeing nowadays is that young people who develop type 2 diabetes have lots of bad fat," he said.
That's fat around the middle and around vital organs such as the liver and heart.
"They come to see me very young, very sick – their livers are full of fat... their hearts are full of fat."
"Their diabetes is a much more aggressive disease than what we see in elderly people," he said.
"It's also much more difficult to treat."
British researchers led by Dr Pierluigi Costanzo, an academic clinical fellow in cardiology at the Universities of Hull and York, collected data from more than 12 000 patients with diabetes for the study and of these about 1 700 had type 1 diabetes, while the rest had type 2 disease.
Over an average of 10 years of follow-up, 9% of the patients had signs of acute coronary syndrome, 7% suffered a stroke, 6% were hospitalised for heart failure and 34% of patients died.
Acute coronary syndrome is an umbrella term for conditions where the blood supplied to the heart muscle is suddenly blocked, said the American Heart Association.
Heart attack and unstable angina (chest pain) are among these conditions.
Most episodes among obese
The researchers found that episodes of acute coronary syndrome were lowest among people with a normal body weight, but became more common as weight increased and were greatest among those who were obese – 49% higher than people with a normal weight.
In addition, among obese patients, the risk of heart failure was 53% higher, and for strokes 25% higher compared to normal-weight patients, the study found.
Death rates in those with type 2 diabetes, however, were lower among obese patients compared to normal-weight patients, but this survival benefit was seen only among the oldest patients while the youngest obese patients had a higher risk of dying, the researchers reported.
For overweight and obese diabetic patients aged 67 and older, the risk of dying was between 18% and 25% lower compared to diabetic patients with a normal weight, the study found.
Although the study found associations between being older and having a lower death risk among diabetes patients, it did not establish a cause-and-effect relationship.
"The notion of an obesity paradox, that some degrees of obesity in some people may confer a favourable rather than unfavourable influence on health outcomes and survival, has been much under scrutiny," said Dr David Katz, director of the Yale University's prevention research centre.
There are three crucial considerations to make sense of this, Katz said.
- "Firstly, the current study is limited to diabetics. One of the most important reasons why obesity is harmful to health is because it causes type 2 diabetes. Once a study is limited to diabetics, identifying further, independent harms of obesity may be far-fetched.
- Doctors know that among elderly patients, losing weight is what people should worry about.
- It does not surprise me that in older people, obesity does not appear as harmful as in younger people. Older people who are managing to keep weight on are likely eating better and are potentially less isolated and perhaps just more vital than those who are not."
A recent study showed more deaths among people who were obese for a greater part of their lifetime, Katz said.
"We should recall that obese people in their seventies did not grow up in a world of epidemic obesity in childhood. Being obese over decades is very different than just gaining weight later in life.
To learn more about obesity, visit the US National Library of Medicine.