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Article History

Received: 11 June 2021

Revised: 7 September 2021

Accepted: 12 October 2021

First Online: 3 January 2022

Declarations

:

: The scientific guarantor of this publication is Hugo Vrenken, PhD.

: I.A. Lie declares no disclosures relevant to the manuscript.E. Kerklingh declares no disclosures relevant to the manuscript.K. Wesnes has received unrestricted research grants from Novartis and Biogen, and speaker honoraria from Biogen.D.R. van Nederpelt declares no disclosures relevant to the manuscript.I. Brouwer has received research support from Merck KGaA, Novartis, and Teva.Ø. Torkildsen has received research grants and speaker honoraria from Biogen, Roche, Novartis, Merck, and Sanofi.K.M. Myhr has received unrestricted research grants to his institution; scientific advisory board, and speaker honoraria from Almirall, Biogen, Genzyme, Merck, Novartis, Roche, and Teva; and has participated in clinical trials organised by Biogen, Merck, Novartis, and Roche.F. Barkhof has received compensation for consulting services and/or speaking activities from Bayer, Biogen Idec, Merck Serono, Novartis, Roche, Teva, Bracco, and IXICO.L. Bø has received unrestricted research grants to his institution and/or scientific advisory board or speaker’s honoraria from Almirall, Biogen, Genzyme, Merck, Novartis, Roche, and Teva; and has participated in clinical trials organised by Biogen, Merck, Novartis, Roche, and Genzyme.H. Vrenken has received research grants from Pfizer, Merck Serono, Novartis, and Teva, speaker honoraria from Novartis, and consulting fees from Merck Serono; all funds were paid directly to his institution.

: No complex statistical methods were used in this paper.

: Written informed consent was obtained from all subjects (patients) in this study.

: The study was approved by the Regional Committee for Medical and Health Research Ethics in Western Norway Regional Health Authority (clinical trials.gov, identifier: NCT00360906).

: Some study subjects or cohorts have been previously reported in “ω-3 fatty acid treatment in multiple sclerosis (OFAMS study): <i>a randomised, double-blind, placebo-controlled trial “</i> by Torkildsen et al., Arch Neurol, 2012. 69(8): p. 1044–51, and in “Low vitamin D, but not tobacco use or high BMI, is associated with long-term disability progression in multiple sclerosis” by Wesnes et al., <i>Mult Scler Relat Disord</i>, 2021. 50: p. 102801.

: • Retrospective• cross-sectional• multicentre study