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Salt and smoking may interact to raise rheumatoid arthritis risk


Smoking is a strong risk factor for developing rheumatoid arthritis. This risk is further amplified by food habits with high sodium intake, says expert.

Smoking is a strong risk factor for developing rheumatoid arthritis. This risk is further amplified by food habits with high sodium intake, says expert.

Eating a diet high in salt may increase the risk of rheumatoid arthritis among smokers, according to a large study from Sweden.

Researchers set out to see if a salty diet might be linked to the onset of rheumatoid arthritis or RA, but found a connection only among smokers – who were more than twice as likely as anyone with a low-salt diet to develop the condition.

“Although we could not confirm our original hypothesis, we were surprised by the large influence of sodium intake on smoking as a risk factor,” Björn Sundström says.

Researchers have discovered that smoking and heavy sodium intake interact to promote RA. 

“Smoking is a strong risk factor for developing rheumatoid arthritis, and this risk is further amplified by less than ideal food habits with high sodium intake,” says Sundström, a researcher in the departments of public health and clinical medicine at Umea University who led the new study.

Rheumatoid arthritis is a chronic disease that causes pain and swelling in the joints.

The cause of rheumatoid arthritis isn’t known, but it results from a person’s own immune system attacking joint tissues. Genetics and lifestyle factors, such as smoking, hormone and cholesterol levels and obesity, have all been identified as risk factors.

Previous laboratory research on animals and human cells also suggests sodium may provoke inflammatory molecules that are often elevated in people several years before RA appears, the authors write in the journal Rheumatology.

To see if there is a link between sodium in the diet and risk for developing RA, Sundström and colleagues looked at health records and lifestyle information of participants in a screening and intervention programme that began in 1991 in Vasterbotton County in northern Sweden.

The study team identified cases of people who developed rheumatoid arthritis and also identified five participants who were similar in age and sex, but did not develop disease, for comparison.

The researchers accounted for dietary habits, education, cholesterol and triglyceride levels, weight and other factors for all the participants and found no significant associations between sodium in the diet and who went on to develop RA.

But when they looked just at smokers, they found those who consumed the most sodium were 2.26 times as likely as smokers who consumed the least sodium to develop RA.

Smokers who consumed the least sodium had similar risk to non-smokers in the study, leading the researchers to conclude that smoking and heavy sodium intake interact somehow to promote RA.

“Ideally, these results needs to be repeated in an independent population,” Sundström, says. More research is also needed to identify the biological pathways through which sodium intake can affect smoking as a risk factor, he says.

The contribution of smoking to risk for rheumatoid arthritis overall is such that 25% of all rheumatoid arthritis in Sweden would not have happened without smoking, says expert. – Filepic

“The study provides the first evidence in rheumatoid arthritis that sodium intake may influence risk for onset of the disease,” says Dr Lars Klareskog, a rheumatologist and researcher at the Karolinska Institute and Karolinska University Hospital in Stockholm, who was not involved in the study.

“In addition, the study demonstrates that the impact of high salt diet is restricted to individuals who smoke,” he says.

Klareskog also notes that smoking is an important risk factor for rheumatoid arthritis.

Researchers would like to see salt intake added to the list of ways avoid rheumatoid arthritis. – Filepic

“The contribution of smoking to risk for rheumatoid arthritis overall is such that 25% of all rheumatoid arthritis in our country, Sweden, would not have happened without smoking,” he says. One third of all cases with the more severe form of rheumatoid arthritis would not have happened without smoking, he added.

The present study suggests that reducing salt intake may be added to this list of lifestyle advice for avoiding rheumatoid arthritis, Klareskog says.

“Confirmatory studies are, however, needed before recommendations on salt intake can be made to the public as ways to protect against getting rheumatoid arthritis,” he said. – Reuters

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