The findings undermined notions about a homogenous Chinese community in Canada, and suggested immigration selection decisions could have health policy implications for decades to come, said endocrinologist Dr Calvin Ke, the lead author of the peer-reviewed study.

“Canadian health care providers need to be aware of the impact of immigration and ethnicity on diabetes. We can’t just lump everyone who is Chinese together into the same category,” said Ke, a University of Toronto Global Scholar who has researched diabetes in Canada and around the world.

“This is what policymakers need to take into account – when your policies select the wealthiest or the highest skilled, the most educated, that will have different implications for health outcomes.”

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Ke said he was not suggesting excluding immigrants on the basis of their possible future health, but that “if we attract a group of people who are skilled and wealthy we have to prepare our health systems to meet their needs”.

For instance, specific strategies were required to tackle obesity among young immigrant men from China, as well as rising rates of diabetes among young Hong Kong and Chinese women, the study said.

The research, based on data from the Ontario Diabetes Database and immigrant arrival records for the province since 1985, compared diabetes incidence among the three immigrant groups, as well as at their places of origin.

Mainland Chinese immigrants had the highest rates of both young-onset diabetes (below the age of 40) and usual-onset diabetes, at 165.5 cases and 1,052.2 cases per 100,000 person-years respectively.

The gap with their fellow immigrants existed across both categories, but was worst among the young. Among young Hong Kong immigrants, the young-onset diabetes incidence rate was 121, and among young Taiwanese, 78.4.

“Although the reasons for these differences are unclear, immigration policies and socioeconomic status may have played a role,” the study said.

“Immigration volumes from China have increased tremendously over the past two decades under policies designed to attract the most wealthy or highly skilled.”

In the five years preceding the 2016 census, 129,020 immigrants came from mainland China, 4,975 from Hong Kong, and 4,310 from Taiwan.

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Among the three immigrant groups, it was only young mainland Chinese men who suffered worse diabetes incidence than the non-Chinese Canadian population. But the rate was rising sharply among young women from China and Hong Kong too, Ke said.

Diabetes, a metabolic disorder characterised by high blood-sugar levels, can lead to a range of complications, including heart and kidney disease, stroke, even blindness. The World Health Organization says it affects about 400 million people and is connected to about four million deaths annually.

Ke, whose co-authors included researchers at the Chinese University of Hong Kong, suggested a relationship between immigrants’ wealth, diabetes rates and economic development in their places of origin.

In mainland China, “it’s the most wealthy who have higher rates of diabetes, and higher rates of obesity, and it could be that these are more the people who are coming to Canada,” Ke said.

Diabetes rates tend to increase as nations develop, bringing richer diets and more sedentary lifestyles to the relatively well-off, previous research has shown.

But on the other hand, in Taiwan – and other places with longer-established economic development, including Canada – the wealthy had lower rates of diabetes and obesity.

Taiwanese immigrants in Canada of all ages similarly had sharply lower diabetes rates than the general population in Taiwan – a reversal of the situation among mainland Chinese immigrants.

Hong Kong, meanwhile, had long been a source of immigrants across a wide range of the economic spectrum, Ke said. Although the incidence of young-onset diabetes among Hongkongers in Canada was about two-thirds higher than in Hong Kong, the usual-onset diabetes rates were almost identical.

Dr David Lau, an endocrinologist at the University of Calgary and the former editor of the Canadian Journal of Diabetes, said that the study provided insights about the diversity of diabetes prevalence among the Chinese diaspora.

“It reminds us that we can’t just use broad strokes about certain ethnicities,” said Lau, who was not involved in the study.

Lau said that his “gut reaction” was to agree with the suggestion that immigration selection was why young Taiwanese immigrants in Canada had such a lower rate of diabetes than in their place of origin.

But he said the study suffered limitations, notably by using data from the province of Zhejiang to calculate Chinese diabetes rates in the absence of nationwide data, something the authors acknowledged.

He said the study lacked enough new information to justify changing public health policies, although it opened the door to new avenues of research.

Economic immigration – including skilled-worker, business, and various wealth-determined programmes – makes up the bulk of Canada’s immigrant intake, representing 58 per cent of all 341,180 admissions in 2019.

Mainland Chinese have dominated wealth-determined immigrant classes in recent years, supplanting Hongkongers and Taiwanese. Canada’s immigrant investor programme and the Quebec immigrant investor programme were the biggest millionaire migration schemes in the world for decades, but the federal version was shut down in 2014, and the Quebec version has been frozen until 2023.

In the past year, Canada has opened up new immigration streams for young people from Hong Kong, in response to concerns about the national security law that was introduced there in 2020.

“As Canada and other countries continue pursuing highly skilled young adult immigrants from Hong Kong, China and other regions, better strategies are required to stem the steep increase in young-onset diabetes, especially among women,” the study said.

Ke said the study, which has been shared with Canada’s immigration department, showed an unexpected facet of the diversity of the Chinese communities.

The study asserted that generalised clinical advice regarding Asians was “problematic”, because all three Chinese immigrant groups “differ tremendously”.

“Immigration happens in waves [and] each wave is selected for different characteristics. Different types of people,” said Ke.

“And while we all may appear to be Chinese, we can see that clinically the risks of diabetes are very different, because the people are actually very different. Socio-economically, they’re different. Languages are different, lifestyles, what they eat. Everything is so diverse and heterogeneous.”