Type 1 Diabetes on the Rise in China, Most New Cases in Adults

Becky McCall

January 15, 2018

In China, two thirds of new type 1 diabetes cases are in adults despite the disease typically developing in the young, the first population-based study of the incidence of the condition across all age groups in China has found.

Results also showed a rapid increase since the mid-1990s in the incidence of type 1 diabetes in those under 15 years of age in a country that has typically had a low incidence of the disease. In this same age group, another novel finding was that higher latitude correlated with a higher disease incidence.

Led by endocrinologist Jianping Weng, MD, PhD, from the Third Affiliated Hospital of Sun Yat-sen University, Guangzhou, China, the authors found that 65.3% of new-onset type 1 diabetes cases were in participants aged 20 years or older.

"We...found that new type 1 diabetes cases are not rare in adults, and we provide nationwide population-based evidence for this assumption for the first time," Dr Weng said.

And there's been an almost four-fold increase in incidence in the under-15s during the past 20 years compared with the Chinese results from the World Health Organization DIAMOND study (Diabetes Care 1998;21:525-529), conducted in the 1990s, he added.

The study findings fill a gap on disease burden of type 1 diabetes in China, updating disease incidence in the under-15s, say the authors, and providing adult incidence data.

They also put a spotlight on the need for more resources, including insulin supplies, to care for people with type 1 diabetes.

"These results should not only update the global map of type 1 diabetes in childhood, but also fill in the blank about the incidence of adult-onset type 1 diabetes," the authors say. The results were published online January 4 in BMJ.

Incidence of Type 1 Diabetes in China Remains Among the Lowest

In this population-based registry study, researchers used data from around 10% of the national population, or around 133 million people, in 13 areas across the country.

Doctors verified cases of type 1 diabetes diagnosed between 2010 and 2013, and then the incidence of type 1 diabetes per 100,000 person-years, stratified by age, sex, and area, was calculated.

Of the 5018 cases of newly diagnosed type 1 diabetes, 1239 were in children under aged 15 years, 1799 in those aged 15–29 years, and 1980 in those aged 30 years or older.

Dr Weng and colleagues note that their estimates in both children and adults in China are still among the lowest reported worldwide.

Although they documented more cases of type 1 diabetes in adults than children, the estimated incidence rate per 100,000 person-years was higher in children as there are many more adults in the population, they note.

Across age groups, the estimated incidence of type 1 diabetes was 1.01 per 100,000 person-years. For patients aged 0–14 years, it was 1.93 per 100,000 person-years, for 15–29 years it was 1.28 per 100,000 person-years, and in those aged 30 or older it was 0.69 per 100,000 person-years.

For under 15s, the estimated incidences were around four-fold higher than reported in DIAMOND (around 0.50 per 100,000 person-years).

The new data show the incidence of type 1 diabetes seems to increase with childhood age and then decrease into adulthood, peaking at 10–14 years at 2.68 per 100,000 person-years, a finding consistent with other large studies in the United States, Japan, and worldwide.

Adult-Onset Type 1 Diabetes a Significant Caseload

Asked what might be driving the increased incidence of disease in adults, Dr Weng said that "possible reasons include change of environment and change of behaviors. Further study is needed to find out the actual reason."

New research from the West shows that the onset of type 1 diabetes is much more common than previously thought in people aged over 30 years compared with younger age groups, as previously reported by Medscape Medical News, with a recent follow-up analysis in December 2017.

The latter analysis showed that 42% of type 1 diabetes cases occurred among individuals age 31–60 years, while 58% were diagnosed prior to age 30.

Type 1 diabetes in adults tends to be drowned out by type 2 diabetes cases, however, and is frequently misdiagnosed as the latter.

Environmental Factors Might Explain Low Incidence of Type 1 Diabetes

A correlation was also seen between the incidence of type 1 diabetes and age, latitude, and exposure to sunlight, with the authors suggesting that environmental factors could influence susceptibility to type 1 diabetes.

Most of the study population were Chinese Han, but "intriguingly, when we compared the northern areas with the southern areas we observed up to a threefold difference in incidence of type 1 diabetes in the 0–14 years group, a finding that has not been reported previously," the authors note.

The estimated incidence in the north (Harbin) was 3.59 per 100,000 person-years and in the south (Chengdu) was 1.14 per 100,000 person-years in the 0–14 years group. The correlation was not seen in those over 15 years.

"Since our study is conducted in a relatively homogeneous population (> 90% of Chinese Han), such association between latitude and type 1 diabetes incidence in the under-15s suggests environmental factors may be responsible, but further study is needed to find out the actual mechanism," the authors observe. 

"Ultraviolet radiation and prevalence of viral infections could contribute to the association of latitude and type 1 diabetes incidence," concluded Dr Weng.

The authors have reported no relevant financial relationships.

BMJ. Published online January 4, 2018. Article

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