Introduction Recently, diabetes prevalence has soared in South Asians making it a global public health priority. However, there are suggestions from the PODOSA trial and elsewhere that pre-diabetes, including impaired glucose tolerance (IGT), may not be increasing. We conducted a systematic review to assess secular trends in pre-diabetes in South Asian populations worldwide.

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, categorised by pre-specified criteria, were used for the primary analysis.

Results 16 cross-sectional data-sets resulting in four sets of repeated cross-sectional studies were identified. Repeated studies conducted in Chennai, rural Tamil Nadu, Mauritius and Singapore (n=30 399), provided time-trend information. Three showed a statistically significant increase in diabetes prevalence (p<0.001) while IGT prevalence fell significantly in two (p<0.05), and was stable in the remainder.

Conclusion This novel systematic review is the first to assess secular trends of pre-diabetes in any population. The data shows diabetes prevalence is rising in South Asians while IGT prevalence is either stable or falling. Recent environmental or lifestyle changes could favour an increased rate of conversion from IGT to diabetes or for individuals to progress directly from normal glycaemic status to diabetes. While the natural history of diabetes remains unclear, these findings have implications for health systems planning future treatment for diabetes and pre-diabetes.