The study did not find any significant association between the development of RA and sodium intake, when all individuals were analysed. There were however significant differences when only current smokers were taken into account, as the sodium intake more than doubled the risk for RA for them.
Dr Björn Sundström, an author of the study, said: "Additive interaction analyses suggested that approximately half (54%) of the increased risk from smoking in the development of RA is due to interaction with sodium intake.
“A large influence of sodium intake on smoking as a risk factor for RA is also supported by the fact that we could not identify any significant proportion of risk from smoking in individuals with a low sodium intake.”
The nested case-control study collected data from around 7.7 years ago as part of a community intervention programme before the RA symptoms' onset.
The researches at Umeå University in Sweden analysed dietary habits and blood samples of 386 individuals with RA symptoms.
Dietary risk factors
“The finding of sodium being a risk factor for the development of RA among smokers is intriguing, as it may explain discrepancies in previous studies of diet as a risk factor for RA.
“That consumption of fruit and vegetables is associated with a lower risk of developing RA, while consumption of protein, red meat, and fish with a medium fat content is associated with a higher risk, could be explained by these dietary products being associated with a higher intake of sodium,” he added.
Published online ahead of print doi: 10.1093/rheumatology/keu330
‘Interaction between dietary sodium and smoking increases the risk for rheumatoid arthritis: results from a nested case control study’
Authors: B. Sundström, I. Johansson, S. Rantapää -Dahlqvist