The findings, published this month in the Annals of the Rheumatic Diseases) suggest that certain dietary fats – not just obesity – may contribute to worsening osteoarthritis.
"Our results suggest that dietary factors play a more significant role than mechanical factors in the link between obesity and osteoarthritis," said Farshid Guilak, PhD, professor of orthopaedic surgery at Duke and the study's senior author.
Primary risk factor
Obesity is one of the primary risk factors for osteoarthritis, although the mechanisms linking these conditions are not fully understood, researchers noted. It has been assumed that increased weight wears the joints out, but this doesn't explain why arthritis is also found in hands and other joints that don't bear weight.
Guilak and his colleagues began studying systemic factors other than body weight to determine their effect on arthritis, and in an earlier study in obese mice, found that the lack of appetite hormone leptin predicted whether the mice had arthritis.
"This made us think that maybe it's not how much weight you gain, but what you eat," Guilak said.
Here the researchers focused on mice with osteoarthritis of the knee caused by injury to the joint. Arthritis resulting from trauma or injury is thought to account for 10 to 15% of all cases of arthritis.
At four weeks of age, mice were fed a low-fat diet or one of the three high-fat diets: One rich in saturated fat; one rich in omega-6 fatty acids; and one rich in omega-6 fatty acids but supplemented with a small amount of omega-3 fatty acids.
At 16 weeks of age, mice underwent surgery to induce knee osteoarthritis in the left hind limb, and ears were punched using 1 mm (right) and 1.5 mm (left) diameter ear punches to examine wound healing. To determine how diet affected behaviour and activity levels, mice were monitored at 6, 14 and 24 weeks of age.
The researchers found that arthritis was significantly associated with the mice's diets, but not with body weight. The mice that ate diets high in saturated fat or omega-6 fatty acids experienced significant worsening of their arthritis, while mice consuming a small supplement of omega-3s had healthier joints.
"While omega-3 fatty acids aren't reversing the injury, they appear to slow the progression of arthritis in this group of mice," Guilak said. "In fact, omega-3 fatty acids eliminated the detrimental effects of obesity in obese mice."
The researchers also looked at the mice's ability to heal wounds, to help them to understand the relationships between arthritis and wound healing. In mice consuming omega-3s, the ear punch healed more quickly than it did in animals that did not receive the supplement.
Guilak said the balance between omega-3s and omega-6s in most western diets was, “way off the scale in the Western diet.”
Annals of the Rheumatic Diseases
July 11, 2014, (http://dx.doi.org/10.1136/annrheumdis-2014-205601 )
‘Dietary fatty acid content as a primary regulator of the pathogenesis of osteoarthritis’
Authors: Chia-Lung Wu, Deeptee Jain, Jenna N. McNeill, Dianne Little, John A. Anderson, Janet L. Huebner, Virginia B. Kraus, Ramona M. Rodriguiz, William C. Wetsel, and Farshid Guilak