People with chronic heart disease who also have diabetes are at higher risk of death and have poorer outcomes than heart patients who do not have diabetes, according to an international study that tracked patients with stable heart disease over five years.

Patients with both diabetes and chronic heart disease are almost 40 per cent more likely to die than those without diabetes. The patients' risk of a combined outcome of heart attack, stroke or death was higher by about 30 per cent.

Before the study, the relationship between diabetes and stable heart disease was less well-known than its relationship with acute heart disease such as a heart attack, said Dr Mak Koon-Hou, the study's first author and a cardiologist at Gleneagles Medical Centre.

"Diabetes has become a double whammy for heart disease. The message is that diabetes is not a nice disease to have, and this is all the more reason to avoid getting it," he added.

The study analysed 32,694 patients with chronic heart disease from 45 countries, including Singapore.

The study underscores the need for diet and exercise to prevent both heart disease and diabetes, said one of its authors, Dr Emmanuelle Vidal-Petiot of Bichat-Claude Bernard Hospital in France, in a statement yesterday.

"Countries worst affected by diabetes are also at the epicentre of the obesity epidemic, which can be in part attributed to urbanisation and associated changes in physical activity and food intake."

Patients with stable heart disease are those who have had a heart attack, have clogged coronary arteries, or have undergone bypass surgery or stenting.

Diabetes is also a major risk factor for heart disease.

Out of the 32,694 patients, close to 30 per cent also have diabetes.

The global prevalence of diabetes is 8.5 per cent, according to the World Health Organisation.

Among the 112 Singapore patients, 23 per cent have diabetes.

The study's findings were published in the European Journal of Preventive Cardiology yesterday for World Health Day.

Diabetes increases the risk of heart disease because high blood sugar levels damage blood vessels and the nerves that control the heart, and contribute to the narrowing of the vessels, said Dr Mak.

He added that the link between both diseases emphasises the need to develop more diabetes medicines that also tackle heart complications.

But preventing diabetes through healthy eating and exercise is still the best approach, he said.

Dr Mak spearheaded the launch of the Healthier Choice Symbol in the late 1990s, as part of his work at the Singapore National Heart Association, now the Singapore Heart Foundation.

He also called for healthier food such as salads to be made more affordable.

Dr Tai E Shyong, director of the Centre for Chronic Disease Prevention and Management under the National University Health System, said there is a misconception that diabetes is only about high sugar intake, whereas people should watch weight gain, which is the key driver of diabetes.

"There's a tendency to think that if you cut down on the amount of sugar we eat, diabetes will go away. It's not that simple. Diabetes may not relate to any single nutrient," said Dr Tai.

"It's more about the total energy balance being affected when we consume more energy than the amount we burn off. Energy balance is critical, and helping people understand this has been incredibly challenging."