ObjectivePeriodontitis is strongly associated with diabetes and is increasingly shown to be associated with other glycemic abnormalities. Vitamin D is postulated to have both anti-inflammatory and antimicrobial activity. Therefore, our aim was to investigate the joint effects of both serum 25-hydroxyvitamin D₃ and total 25-hydroxyvitamin D with periodontitis on homeostatic model assessment for insulin resistance (HOMA-IR), pre-diabetes, and type 2 diabetes.Research design and methodsUsing data from the 2009–2010 National Health and Nutrition Examination Survey, the sample was restricted to adults over 30 years of age, who were eligible for oral health examination, and had vitamin D, fasting glucose and insulin measures. The analytic sample includes those with (n=1631) and without (n=1369) type 2 diabetes. Using survey logistic multivariable regression analysis, we examined the following joint effects: (1) vitamin D insufficiency (<50 nmol/L) and moderate to severe periodontitis (VD+PD+); (2) vitamin D insufficiency and mild to no periodontitis (VD+PD−); and (3) vitamin D sufficiency ) (>50 nmol/L) and periodontitis (VD−PD+), and compared these groups with the doubly unexposed reference group (VD−PD−).ResultsConsistently, the joint effects of vitamin D₃ insufficiency and total vitamin D insufficiency with periodontitis (VD+PD+) were significantly associated with diabetes: OR=2.83 (95% CI 1.34 to 5.96) and OR=1.98 (95% CI 1.04 to 3.76), respectively. However, the joint effects of vitamin D₃ insufficiency and periodontitis were attenuated for HOMA-IR 4.17: OR=1.57 (95% CI 0.97 to 2.55). Pre-diabetes was not associated with either joint effects.ConclusionIn this cross-sectional, nationally representative sample, the joint effects of vitamin D and periodontitis appear to differ for HOMA-IR, pre-diabetes and diabetes.