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.

KEYWORDS:

• Dietary inflammatory index
• additive interaction
• multiple sclerosis
• case–Control
• population-based
• incident cases
• population control
• interaction

Acknowledgments

The authors appreciate the cooperation of the staff members of the IMSS.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Ethical approval

The study was approved by the ethics committee of Tehran University of Medical Sciences (approval number: 127334-26145-188-02-93).

Data availability statement

Data described in the manuscript, code book, and analytic code will be made available upon request pending approval by the authors.

Additional information

Funding

This project has been a part of Ibrahim Abdollahpour’s PhD dissertation in epidemiology (Dissertation Project Number: 93-04-10–240/691). The study was funded by Tehran University of Medical Sciences and Multiple Sclerosis Research Center.

Notes on contributors

Ibrahim Abdollahpour

Dr. Ibrahim Abdollahpour, PhD, is an Epidemiologist at Isfahan University of medical sciences, Iran. His research interest focuses on case-control studoes as well as causal inference.

Yahya Salimi

Dr. Yahya Salimi, PhD, is an Epidemiologist at Kermanshah University of medical sciences in Iran. His research interest focuses on social epidemiology and causal inference.

Saharnaz Nedjat

Professor Saharnaz Nedjat is full Professor of Epidemiology at Tehran University of medical sciences in Iran. Her research interest focuses on social epidemiology and quality of life.

Maryam Nazemipour

Dr. Maryam Nazemipour is biostatistician in Osteoporosis Research Center, Endocrinology and Metabolism Clinical Sciences Institute, Tehran University of Medical Sciences, Tehran, Iran.

Mohammad Ali Mansournia

Professor Mohammad Ali Mansournia is full Professor of Epidemiology at Tehran University of medical sciences in Iran. His research interest focuses on causal inference.

Bianca Weinstock-Guttman

Professor Bianca Weinstock-Guttman is Professor of Neurology at Jacobs School of Medicine and Biomedical Sciences, SUNY Buffalo.