Dietary insulin index and insulin load in relation to glioma: findings from a case-control study.

BACKGROUND: Although hyperinsulinemia is assumed to be involved in brain carcinogenesis, data on the link between dietary insulin index (DII) and dietary insulin load (DIL) and risk of glioma are lacking. OBJECTIVE: The current study aimed to investigate the relation between DII and DIL and risk of glioma in a case-control study among Iranian adults. METHODS: In this hospital-based case-control study, 128 pathologically confirmed cases of glioma and 256 age and sex-matched controls were enrolled. Dietary intakes of study participants were assessed using a validated Block-format 123-item semi-quantitative FFQ. DII and DIL were computed using a published food insulin index (FII) data. RESULTS: A significant positive association was found between DIL and glioma (OR: 3.56; 95% CI: 1.85-6.58, P < 0.001); such that after controlling for potential confounders, participants in the highest quartile of DIL had 2.95 times greater odds of glioma than those in the lowest quartile (OR: 2.95; 95% CI: 1.40-6.24, Ptrend = 0.006). Furthermore, we observed a significant positive association between DII and glioma (OR: 2.65; 95% CI: 1.43-4.93, Ptrend = 0.001). This association remained significant even after considering energy intake (OR: 2.66; 95% CI: 1.43-4.95, Ptrend = 0.001). However, when further potential confounders were taken into account, this relationship became non-significant (OR: 1.87; 95% CI: 0.92-3.80, Ptrend = 0.03), despite a significant trend of increased odds ratios (P = 0.03). CONCLUSIONS: In conclusion, we found a significant positive association between DIL and odds of glioma. DII was not significantly associated with odds of glioma after controlling for confounders.