Vitamin B12 and risk of diabetes: new insight from cross-sectional and longitudinal analyses of the China Stroke Primary Prevention Trial (CSPPT)

Introduction Previous studies in mostly Western populations have yielded conflicting findings on the association of vitamin B-12 with diabetes risk, in part due to differences in study design and population characteristics. This study sought to examine the vitamin B-12-diabetes association in Chinese adults with hypertension by both cross-sectional and longitudinal analyses. Research design and methods This report included a total of 16 699 participants from the China Stroke Primary Prevention Trial, with pertinent baseline and follow-up data. Diabetes mellitus was defined as either physician-diagnosed diabetes, use of glucose-lowering drugs, or fasting blood glucose (FBG) >= 7.0 mmol/L. New-onset diabetes was defined as any new case of onset diabetes during the follow-up period or FBG >= 7.0 mmol/L at the exit visit. Results At baseline, there were 1872 (11.2%) patients with diabetes; less than 1.5% had clinical vitamin B-12 deficiency (<148.0 pmol/L). Over a median follow-up period of 4.5 years, there were 1589 (10.7%) cases of new-onset diabetes. Cross-sectional analyses showed a positive association between baseline vitamin B-12 levels and FBG levels (beta=0.18, 95% CI 0.15 to 0.21) and diabetes (OR=1.16, 95% CI 1.10 to 1.21). However, longitudinal analyses showed no association between baseline vitamin B-12 and new-onset diabetes or changes in FBG levels. Among a subset of the sample (n=4366) with both baseline and exit vitamin B-12 measurements, we found a positive association between an increase in vitamin B-12 and an increase in FBG. Conclusions In this large Chinese population of patients with hypertension mostly sufficient with vitamin B-12, parallel cross-sectional and longitudinal analyses provided new insight into the conflicting findings of previous studies, and these results underscore the need for future studies to consider both baseline vitamin B-12 and its longitudinal trajectory in order to better elucidate the role of vitamin B-12 in the development of diabetes. Such findings would have important clinical and public health implications.