By Mary Elizabeth Dallas
FRIDAY, Sept. 12, 2014 (HealthDay News) -- Consuming too much salt may more than double a smoker's risk of developing the painful inflammatory disease known as rheumatoid arthritis, a new study finds.
The study, published online Sept. 10 in the journal Rheumatology, involved 386 people who reported their eating habits for about eight years before they developed symptoms of rheumatoid arthritis.
The researchers examined health-screening data on the study participants, including physical activity levels, whether or not they smoked, and blood samples. This data was compared to a "control group" of nearly 1,900 similar people.
The investigators found no significant link between salt intake alone and the development of rheumatoid arthritis in any of the patients. They did find, however, a link between high salt intake and a more than doubled risk for rheumatoid arthritis in smokers.
According to the new analysis, "approximately half [54 percent] of the increased risk from smoking in the development of rheumatoid arthritis is due to interaction with sodium [salt] intake," Bjorn Sundstrom, from the department of public health and clinical medicine, rheumatology at Umea University, said in a journal news release.
"A large influence of sodium [salt] intake on smoking as a risk factor for rheumatoid arthritis is also supported by the fact that we could not identify any significant proportion of risk from smoking in individuals with a low sodium [salt] intake," Sundstrom added.
The findings could help scientists gain a better understanding of the development of rheumatoid arthritis among smokers, the study authors suggested.
"The finding of sodium [salt] being a risk factor for the development of rheumatoid arthritis among smokers is intriguing, as it may explain discrepancies in previous studies of diet as a risk factor for rheumatoid arthritis," Sundstrom said.
"That consumption of fruit and vegetables is associated with a lower risk of developing rheumatoid arthritis, 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 [salt]," he said.
Although the study found an increased risk of rheumatoid arthritis in people who both smoked and had high salt intake, the association seen in the study does not prove a cause-and-effect relationship.