No association between dietary sodium intake and the risk of multiple sclerosis

Abstract

Objective: To prospectively investigate the association between dietary sodium intake and multiple sclerosis (MS) risk.

Methods: In this cohort study, we assessed dietary sodium intake by a validated food frequency questionnaire administered every 4 years to 80,920 nurses in the Nurses' Health Study (NHS) (1984-2002) and to 94,511 in the Nurses' Health Study II (NHSII) (1991-2007), and calibrated it using data from a validation study. There were 479 new MS cases during follow-up. We used Cox proportional hazards models to estimate hazard ratios (HR) and 95% confidence intervals (CI) for the effect of energy-adjusted dietary sodium on MS risk, adjusting also for age, latitude of residence at age 15, ancestry, body mass index at age 18, supplemental vitamin D intake, cigarette smoking, and total energy intake in each cohort. The results in both cohorts were pooled using fixed effects models.

Results: Total dietary intake of sodium at baseline was not associated with MS risk (highest [medians: 3.2 g/d NHS; 3.5 g/d NHSII] vs lowest [medians: 2.5 g/d NHS; 2.8 g/d NHSII] quintile: HR_pooled 0.98, 95% CI 0.74-1.30, p for trend = 0.75). Cumulative average sodium intake during follow-up was also not associated with MS risk (highest [medians: 3.3 g/d NHS; 3.4 g/d NHSII] vs lowest [medians: 2.7 g/d NHS; 2.8 g/d NHSII] quintile: HR_pooled 1.02, 95% CI 0.76-1.37, p for trend = 0.76). Comparing more extreme sodium intake in deciles yielded similar results (p for trend = 0.95).

Conclusions: Our findings suggest that higher dietary sodium intake does not increase the risk of developing MS.

Figure 1. Flowchart of the study population selection and sample size

MS = multiple sclerosis; NHS = Nurses' Health Study; NHSII = Nurses' Health Study II.

Figure 2. Total dietary sodium intake in deciles and multiple sclerosis risk in Nurses' Health Study (1984–2004) and Nurses' Health Study II (1991–2009)

Total dietary sodium intake assessed by food frequency questionnaire at baseline was adjusted for energy intake using the residual method and subsequently calibrated using data from the Women's Lifestyle Validation Study.^, Pooled hazard ratios (HR) and 95% confidence intervals (CI) adjusted for age, latitude of residence at age 15 (north, middle, south), ancestry (southern European, Scandinavian, other Caucasian, other), pack-years of smoking (0, <10, 10–24, ≥25), supplementary vitamin D intake (0, <400, ≥400 IU/d), body mass index at age 18 (<18.5, 18.5–<25, 25–<30, ≥30 kg/m²), and total energy intake.