Is there a divergence in time trends in the prevalence of impaired glucose tolerance and diabetes? A systematic review in South Asian populations.

OBJECTIVE: Recently, diabetes prevalence has increased in South Asians making it a global public health priority. There are suggestions that pre-diabetes, including impaired glucose tolerance (IGT), may not be increasing. We conducted a systematic review to explore the paradox. Research Design and Methods We searched electronic databases from inception to June 2009 for cross-sectional studies providing prevalence of pre-diabetes (using WHO criteria) in South Asian adult populations. Two reviewers independently screened articles, performed data extraction, quality appraisal and study classification with any discrepancies resolved by consensus. Repeated cross-sectional studies, categorized by pre-specified criteria, were used for the primary analysis, supplemented by analysis of comparable and all studies.
RESULTS: In total, 79 cross-sectional data sets (from 69 published studies) were identified resulting in the inclusion of 179 408 people. Four sets of repeated cross-sectional studies, conducted in Chennai, rural Tamil Nadu, Mauritius and Singapore (n = 30,399), provided time trend information. Three of them showed an increase in diabetes prevalence (P < 0.001) whereas IGT fell in two (P < 0.05), and was stable in the remainder. A similar pattern was seen among three other sets of comparable studies (n = 58,820) and in scatterplots of all 79 data sets.
CONCLUSION: This novel systematic review is the first to assess secular trends of pre-diabetes in any population. The data show diabetes prevalence is rising, whereas IGT prevalence is stable or falling. Explanations include: recent environmental or lifestyle changes favouring an increased rate of conversion from IGT to diabetes, or a cohort effect with improving maternal and infant nutrition resulting in reduced IGT with a fall in diabetes to follow.