SINGAPORE - 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 also have diabetes, according to an international study that tracked heart patients on a registry over five years.

It found that patients who had both diabetes and chronic heart disease were almost 40 per cent more likely to die than those without diabetes.

The diabetic patients' risk of a heart attack, stroke or death was also higher by about 30 per cent.

Before the study, the relationship between diabetes and stable heart disease was less well-known than that between diabetes and 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 112 from Singapore - in Europe, Asia, America, the Middle East, Australia, and Africa. Patients were enrolled between 2009 and 2010.

It underscores the importance of preventive measures, said the study's author, Dr Emmanuelle Vidal-Petiot of the Bichat-Claude Bernard Hospital in France.

"Obesity and lack of exercise are common risk factors for both diabetes and heart disease and our results highlight the urgent need to improve nutrition and raise activity levels globally," said Dr Vidal-Petiot in a statement on Wednesday (April 7).

"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, clogged coronary arteries, or undergone bypass surgery or stenting.

Out of the 32,694 patients on the registry, 29 per cent, or 9,502 patients, had diabetes. The global prevalence of diabetes is 8.5 per cent, according to the World Health Organisation.

Among the Singapore patients, 23 per cent had diabetes.

The study's findings were published in the European Journal of Preventive Cardiology on Wednesday 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.

Among the various groups of diabetes medications, only two groups have been shown to address heart complications, and they were developed only four to five years ago, said Dr Mak.

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 green 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, 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.

"Many of my patients tell me that they eat brown rice, but they still cannot lose weight. What they don't seem to realise is that brown rice is healthier than white rice, and blood sugar goes up less after it is consumed, but energy content in a bowl is about the same for both.

"So it is not surprising that simply substituting brown rice for white rice may not lead to weight loss."