Efficacy of High-Dose Fish Oil Not Significantly Different from Low-Dose in Knee OA

SAN DIEGO, CA—Patients with symptomatic knee osteoarthritis had preservation or a slight increase in cartilage volume whether treated with low-dose or high-dose fish oil supplementation for 2 years, investigators reported at the 2013 ACR/ARHP Annual Meeting.

“The lack of a decrease in both groups is unexpected and may imply that both therapies have chondroprotective properties,” noted Lynette March, MD, PhD, of the University of Sydney, Institute of Bone and Joint Research, Royal North Shore Hospital, St. Leonards NSW, Australia, and colleagues.

Although fish oil is widely used for the symptomatic treatment of osteoarthritis, its effect on cartilage volume has not been investigated in a randomized controlled trial. “The objective of this study was to determine whether high-dose fish oil is superior to low-dose fish oil in retarding structural progression of symptomatic knee osteoarthritis,” they noted. The multicenter, 24-month, double-blind trial was investigator-initiated and funded by the government.

A total of 202 patients >40 years of age with knee osteoarthritis (ACR criteria) with regular knee pain were randomized to high-dose fish oil liquid (EPA 18% and DHA 12%) 15mL/day or low-dose fish oil (blend of fish oil and sunflower oil in a ratio of 1:9) 15mL/day. “Each oil was also flavored with citrus to provide a comparable taste and ensure masking,” Dr. Hill stated.

“Prior to randomization, a 4-week run-in period with a similar oil was performed to exclude patients who were intolerant to liquid fish oil,” they explained. The OARSI Atlas was used to score baseline knee radiographs. Co-primary end points were change in cartilage volume (medial tibial, lateral tibial, patellotibial) from baseline to 24 months and WOMAC pain score (results of which were previously reported). Paired MRI data analysis was performed in both intent-to-treat and per-protocol populations.

“There was significantly greater and earlier dropout in the high dose group (34.6%, median 3 months) compared to the low dose group (19.8%, median 7.5 months),” Dr. Hill reported. Excluded were 51 patients from one site due to technical issues with baseline MRI data; an additional 35 were excluded due to lack of paired MRI data.

The OARSI joint space narrowing and osteophyte scores did not differ between the groups. In the intent-to-treat analysis (n=116), “both groups demonstrated preservation or a slight increase in cartilage volume in each compartment over time, with no significant difference seen between the two groups,” they noted.

Further, a higher proportion of patients in the low-dose group had a bone marrow lesion size decrease larger than the least significant change at any site within their knee (55% vs. 40%; P=0.127). Those in the low-dose group had a greater chance (RR 1.56, 95% CI 1.03—2.38; P=0.038) of having a bone marrow lesion size decrease at any site within their knee.

“Similarly, per protocol analysis (n=99) demonstrated no decrease over time or difference between groups.” High-dose fish oil for 2 years was not significantly different in its effect on cartilage volume or bone marrow lesions in patients with symptomatic knee osteoarthritis, concluded researchers.
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