At 18, David was diagnosed with Type 2 diabetes.

Within three years, he had macular oedema, a diabetic eye disease linked to leaking blood vessels, which left fluid accumulating in part of his retina.

David was told that if the condition was left untreated, he could go blind.

So he underwent laser treatment.

In the next five years, he underwent two operations to remove lumps on his leg and neck.

The early detection of the lumps saved his leg from being amputated, recalled David, who wanted to be known only by his first name.

The 31-year-old does not have any kidney problems now.

But a new study found that people like David, who have been diagnosed with Type 2 diabetes in early adulthood, will see their renal function deteriorate up to three times faster.

They will also face a higher risk of chronic kidney disease.

Compared with the majority of patients who get diabetes between 40 and 60 years old, those diagnosed before 30 with Type 2 diabetes also face a higher risk of heart disease due to a faster decline in their kidney function.

The complications may occur less than 10 years after their diabetes diagnosis, the study by researchers at Khoo Teck Puat Hospital (KTPH) has found.

"I was shocked when I was told that I had diabetes during my pre-enlistment check-up for national service.

"I was still studying in ITE and I wasn't insured," said David, who later obtained a polytechnic diploma.

Living with diabetes for the past 13 years means he has to take medication every day, visit the doctor at least once a month and watch his sugar intake.

All these might seem like small inconveniences.

However, the part-time security officer, who is still uninsured, is constantly worrying about a lifetime of medical expenses and the higher chances of getting kidney failure.

What was once considered an ageing-related disease has been rapidly diagnosed in young adults and even teenagers in the past two to three decades.

One in nine Singaporeans has diabetes, and one in three has a lifetime risk of developing the disease.

If nothing is done, the number of diabetics under age 70 is expected to rise to 670,000 by 2030 and to one million by 2050.

The recent findings by KTPH are important as Singapore is second only to the United States in having the highest incidence of diabetes among developed nations.

Between 2011 and 2014, 1,189 patients were recruited from KTPH and Yishun Polyclinic for the study.

Led by Associate Professor Lim Su Chi, the study tracked the patients' kidney function for almost four years, tabulating the changes yearly.

About 13 per cent or 157 patients fell under the early onset group and were found to have a higher body mass index and poorer blood glucose control.

Many rely on insulin injections for diabetes control.

Many already had kidney injury - leakage of albumin into their urine - shortly after their diagnosis of diabetes, said Dr Liu Jianjun, who was involved in the study.

Eighty per cent of the patients with early onset diabetes are overweight.

There are also more smokers among the younger patients, he said, adding that smoking is a known risk factor in kidney disease progression.

Dr Liu said traditional risk factors such as obesity and poorer diabetes control only partially explain the excess risk in this group of patients.

Some social behaviour factors such as smoking may also contribute to the excess risk.

In Singapore, the prevalence of Type 2 diabetes in early adults between 18 and 30 remains unknown.

But in the US youth population aged 10 to 18, the incidence of Type 2 diabetes increases at a rate of 4.8 per cent each year.

Dr Liu said the rapidly rising prevalence of obesity in the young is believed to be the root cause of early onset Type 2 diabetes.

He added that this calls for a concerted effort to promote healthy lifestyles, and increasing physical activities for children and adolescents to control their body weight and reduce the risk of developing diabetes in early adulthood.