Put down that cigarette and put away the bag of potato chips.
Smoking and eating salty foods not only raise your risk of cardiovascular disease –- they more than double your risk of developing rheumatoid arthritis (RA), according to a new study published online in the journal Rheumatology.
That is the unexpected finding of researchers in Sweden, who wanted to know if high sodium intake was associated with RA, as some animal and human cell studies have suggested. They focused their research on 386 people diagnosed with RA in northern Sweden who were enrolled in a long-term cardiovascular study known as the Västerbotten Intervention Program (VIP). Participants in that study provided detailed information about their health and eating habits starting in 1991.
To their surprise, researchers did not find any significant association between high sodium intake and the developed of RA. However, when they dug deeper into the data, they found that smokers who ate a lot of salty food had twice the risk of developing RA as a control group.
Smoking alone was not associated with rheumatoid arthritis, it was only when the two bad habits were combined that the added risk of RA was found.
“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,” said lead author Björn Sundström of the Department of Public Health and Clinical Medicine, Rheumatology at Umeå University, Sweden.
“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. These results could have implications for analyses of diet in other conditions in which inflammation is of importance.”
While some foods were major contributors to high sodium intake, the researchers were unable to identify any specific food that helped “trigger” RA. Previous studies have suggested that fish, fruit and vegetables have a protective effect against RA, while red meat and proteins have a deleterious effect.
Why smoking and sodium have such a pronounced effect on RA risk is unclear. Earlier studies on humans have suggested that sodium plays a role in the development of autoimmune diseases like RA by creating antibodies that promote inflammation.
Rheumatoid arthritis is a chronic autoimmune disease in which the body’s own defenses attack the tissues lining the joints, causing painful swelling, inflammation and bone erosion. As the disease progresses, many RA patients become significantly disabled. About 1.5 million Americans and 1% of adults worldwide suffer from RA.
Recent research has linked two protein molecules to the development of rheumatoid arthritis. Researchers at the University of Illinois at Chicago College of Medicine found high levels of the proteins in the joints of patients affected by the disease.
Smoking has also been associated with RA in previous studies. Swedish researchers found that the number of cigarettes a woman smokes a day and the number of years they smoked significantly increases the risk of rheumatoid arthritis (RA) by as much as 70%.
A study at the University of Rochester of more than 5,300 patients with spinal disorders and back pain found that those who quit or never smoked had less pain than those who continued to smoke.
And a study by researchers at the University of Kentucky discovered that women who smoked heavily more than doubled their odds of experiencing chronic pain.