Additive interaction between dietary inflammatory index and some key risk factors of multiple sclerosis: a population-based incident case-control study

Abstract

BACKGROUND: Recently, dietary inflammatory index (DII) has been introduced as a significant risk factor for MS. We examined the interaction between dietary inflammatory index and some formerly demonstrated key risk factors of multiple sclerosis (MS). MATERIAL AND METHODS: We conducted a population-based incident case-control study of 547 MS cases and 1057 controls. Multiplicative and additive interaction were assessed using interaction term in the logistic regression model and synergy index (SI), respectively. RESULTS: Additive interaction was detected between DII and drug abuse (SI = 2.58; 95 CI: 1.14-5.82), gender (SI = 2.00; 95 CI: 1.39-2.87) and history of depression (SI = 1.68; 95 CI: 1.04-2.72) on the risk scale. The risk of MS in drug abusers with DII >/= 0 was 10.4-times higher than that in non-drug abusers with DII < 0 (OR = 10.4, 95 CI: 5.12-21.02, P < 0.001). We also found that women with DII >/= 0 had a 9.2 times larger risk compared with the men with DII < 0(OR = 9.2, 95 CI: 6.3-13.5, P < 0.001). Similarly, the risk of MS was remarkably higher in those with a history of depression and DII >0 (OR = 7.6, 95 CI: 5.1-11.5, P < 0.001). There was no evidence of multiplicative interaction between DII and the other risk factors of MS on the risk scale. CONCLUSIONS: We identified additive interaction between DII and drug abuse, gender and history of depression on MS. Further studies are needed to understand the underlying mechanisms of these detected interactions.