VIENNA — Not only are South Asians (of Indian, Pakistani, and Bangladeshi origin) more likely to develop type 2 diabetes compared with whites, they also have a faster trajectory of disease development, according to new research from the United Kingdom.
In the years preceding a diagnosis of diabetes, fasting glucose levels rose more quickly and insulin sensitivity dropped more sharply among South Asians than among whites, reported Dr. Adam Tabak, from University College London, United Kingdom, and Semmelweis University, in Budapest, Hungary, here at the European Association for the Study of Diabetes 2014 Meeting.
When fasting plasma glucose levels began to rise, white participants were able to increase insulin secretion for up to 7 years before they were diagnosed with diabetes, but South Asian people seem to lack this compensatory mechanism, he noted.
The study shows that "beta cells become exhausted…earlier in South Asians, highlighting the need for earlier detection of diabetes…[and earlier] preventive efforts in South Asian populations" to take advantage of this shorter window of opportunity in this ethnic group, Dr. Tabak told Medscape Medical News.
Unraveling Ethnic Differences in Diabetes
The reasons that South Asians have a higher prevalence of type 2 diabetes than whites are poorly understood, but the epidemiologic Whitehall II study of civil servants in the United Kingdom has helped to unravel some ethnic differences, Dr. Tabak explained.
In previous work, he and his colleagues showed that among South Asians, glucose tolerance declined more rapidly with age compared with whites; moreover, insulin secretion was inadequate to compensate for declining insulin sensitivity.
The current analysis aimed to investigate changes in fasting and 2-hour postload glucose levels, insulin sensitivity, and beta-cell function in 101 South Asian participants and 764 white participants in the Whitehall II study before they were diagnosed with diabetes. The participants were followed from 1992 to 2009.
A notable strength of the study is that the researchers determined glucose and insulin levels based on up to 4 repeat measures every 5 years, Dr. Tabak said.
About two-thirds of the participants were male. At baseline, they had a mean age of 50, and they developed diabetes at a mean age of 62.
At baseline, compared with whites, South Asians had similar fasting glucose and insulin secretion levels, but they had higher 2-hour postload glucose and insulin levels and lower insulin sensitivity. They were also less physically active and ate a less healthy diet, and they were more likely to work in a lower occupational grade.
Diabetes was diagnosed by a 75-g oral glucose-tolerance test in half the participants and by self-report (along with or without reported use of antidiabetic agents) in the others.
South Asians were almost 3 times as likely to develop diabetes during follow-up compared with whites (26.4% vs 10.2%), which was not unexpected, according to Dr. Tabak.
New Findings Extend Prior Observations
However, the study also identified that fasting plasma glucose levels rose by 0.34 mmol/L per decade faster among South Asians than among whites.
At the time of their diabetes diagnosis, plasma glucose levels were 0.36 mmol/L higher in the South Asians than in the whites.
Insulin secretion (beta-cell function) increased in both ethnicities from 15 years to until 7 years before the diagnosis of diabetes, but this increase, a compensatory mechanism, was notably larger in whites and in fact could hardly be seen in South Asians; in the next 7 years, the decline in the trajectories was the same in both groups.
"These findings extend our prior observation of inadequate pancreatic beta-cell compensation with aging in healthy South Asians," Dr. Tabak said.
"We hypothesize that, given their decreased insulin sensitivity that — according to previous observations in children — develops at an early age, way before the baseline of our diagnosis, South Asians have an inadequate insulin secretory reserve and are unable to increase their insulin secretion 15 to 7 years before diabetes diagnosis," he observed.
"This also leads to a faster increase in their fasting glucose preceding diabetes diagnosis."
He added that although the mechanisms behind these differences are unknown, "we think this includes both environmental and genetic factors." But "surprisingly, the adjustment for lifestyle and social factors had hardly any effect on the differences."
Dr. Tabak has reported no relevant financial relationships.
European Association for the Study of Diabetes 2014; September 16, 2014; Vienna, Austria. Abstract 61
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Cite this: Rapid Diabetes Course in South Asians; Early Prevention Urged - Medscape - Sep 16, 2014.