High levels of circulating vitamin d are required to prevent leaky gut-associated inflammation in subjects at risk for diabetes

Gut microbiota has a significant role in the development of obesity-associated inflammation and its metabolic complications. This may be partially explained by the “ leaky gut” hypothesis by which gut bacterial LPS is released in the circulation through compromised tight junctions (TJ) triggering a state of low grade inflammation. The LPS signaling pathway requires the interaction between the cell-bound CD14 and LPS-binding protein (LBP). An increase in anti-LPS core antibodies (Abs) and LBP are suggested to have anti-inflammatory effects. An increase in zonulin, a novel marker of intestinal barrier integrity, has been related to leaky TJ. Serum vitamin D (25D) has a gut protective role in inflammatory bowel disease, but its role on the leaky gut associated with obesity and prediabetes is unknown. Aim: To assess the leaky gut - related inflammatory profile of African-American men (AAM) with hypovitaminosis D, pre-diabetes, and obesity and evaluate whether changes in inflammatory markers (IM) are related to 25D levels and metabolic parameters (BMI and A1c). Methods: Subjects were AAM from the D-Intervention at Veterans Affairs trial (DIVA, NCT01375660), treated with weekly placebo (n=20) or ergocalciferol 50,000 IU (n=38) for 12 months (mo). Subjects were selected if they had valid stool samples for microbiota analysis. Serum was collected at 0 and after 12 mo of treatment for analysis of IM such as soluble CD14 (ng/ml), LBP (ng/ml), LPS Abs (GMU/ml), and zonulin (ng/ml). Comparisons were made between 0 vs 12mo and between extreme quartiles (low vs high levels) of 25D, BMI and A1c at 12mo. Results: Baseline subject mean characteristics (n=58, age 60yo, BMI 32.4, A1c 6.2) and IM levels did not significantly change between 0 and 12 mo, while serum 25D increased from 12 to 44 (p<0.001). Comparison of High vs Low 25D quartiles (11 vs 75, median 50) showed that LPS Abs and LBP were significantly higher in High 25D (268 vs 114, p=0.01) and (19074 vs 12360, p=0.03), respectively, while sCD14 was significantly lower in High 25D (3436 vs 6334; p< 0.001), and zonulin did not change. However, zonulin significantly decreased (7.6 to 6.3; p=0.05) in High 25D from 0 to 12 mo, as 25D increased from 14 to 75 (p<0.001). In High BMI quartile, a decrease in zonulin from 5.1 to 3.4 (p=0.04) and sCD14 from 5708 to 3420.8 (p=0.04) were seen from 0 to 12mo, as 25D increased from 13 to 56 (p<0.001). IM did not significantly change across quartiles or time for A1c. Conclusions: Results suggest that serum 25D may have protective effects on the gut barrier and prevent the low-grade systemic inflammation induced by a leaky gut. The beneficial effects of 25D were related to the 25D levels and obesity status (BMI); 25D levels >50ng/dl were required to impact LPS Abs, LBP, and sCD14, while even higher 25D were required to lower zonulin. Further research is needed to explore whether 25D levels > 50-75 could prevent leaky gut-associated conditions like diabetes.