Postprandial glycemic fluctuations after gastrectomy are seen in patients with gastric cancer but, no studies have investigated the association between gastrectomy and type 2 diabetes mellitus (T2DM) in gastric cancer survivors. This study aimed to elucidate the relationship between gastrectomy (total or subtotal) and incident T2DM. In addition, we explored whether vitamin B12 supplementation modulates this risk among patients who have undergone total gastrectomy.

In this large nationwide population-based retrospective cohort study using the National Health Insurance Service database of South Korea, we identified patients aged >20 years who underwent gastrectomy from 2008 to 2015 (n = 150,074) and age- and sex-matched controls without gastrectomy (n = 301,508). A Cox proportional hazards model was used.

During the median follow-up duration of 4.4 years after the 2-year time lag after gastrectomy, of the 78,006 subjects, 4,597 (5.9 %) developed T2DM. Compared with matched controls, the adjusted hazard ratio (AHR[95 % confidence interval]) for T2DM of patients with total gastrectomy was 1.34[1.23;1.47]. The corresponding AHR after subtotal gastrectomy was 0.81[0.76;0.86]. Among the patients with total gastrectomy, the risk of T2DM was significantly increased in those who did not receive any vitamin B12 supplementation (AHR=1.60[1.33;1.92]), whereas the risk of T2DM was lower (close to being statistically significant) in those who received continuous vitamin B12 supplementation after gastrectomy (AHR=0.70[0.49;1.01]).

These results show a significantly reduced risk of T2DM in gastric cancer patients undergoing subtotal gastrectomy and a significantly increased risk of T2DM in gastric cancer patients undergoing total gastrectomy, which is mitigated by continuous vitamin B12 supplementation.