Abstract
We conducted a systematic review and meta-analysis to assess the effects of increasing dietary omega-3, omega-6 and mixed polyunsaturated fatty acids (PUFA) on musculoskeletal health, functional status, sarcopenia and risk of fractures. We searched Medline, Embase, The Cochrane library, ClinicalTrials.gov and the WHO International Clinical Trials Registry Platform (ICTRP) databases for Randomised Controlled Trials (RCTs) of adults evaluating the effects of higher versus lower oral omega-3, omega-6 or mixed PUFA for ≥ 6 months on musculoskeletal and functional outcomes. We included 28 RCTs (7288 participants, 31 comparisons), 23 reported effects of omega-3, one of omega-6 and four of mixed total PUFA. Participants and doses were heterogeneous. Six omega-3 trials were judged at low summary risk of bias. We found low-quality evidence that increasing omega-3 increased lumbar spine BMD by 2.6% (0.03 g/cm2, 95% CI - 0.02 to 0.07, 463 participants). There was also the suggestion of an increase in femoral neck BMD (of 4.1%), but the evidence was of very low quality. There may be little or no effect of omega-3 on functional outcomes and bone mass; effects on other outcomes were unclear. Only one study reported on effects of omega-6 with very limited data. Increasing total PUFA had little or no effect on BMD or indices of fat-free (skeletal) muscle mass (low-quality evidence); no data were available on fractures, BMD or functional status and data on bone turnover markers were limited. Trials assessing effects of increasing omega-3, omega-6 and total PUFA on functional status, bone and skeletal muscle strength are limited with data lacking or of low quality. Whilst there is an indication that omega-3 may improve BMD, high-quality RCTs are needed to confirm this and effects on other musculoskeletal outcomes.
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Key Points
Omega-3 is suggested to exhibit protective effects on bone and muscle whilst omega-6 is thought to have pro-inflammatory effects with detrimental consequences to musculoskeletal health. A higher omega-3: omega-6 ratio is proposed as beneficial. Effects of total PUFA have not been investigated recently. This systematic review was conducted to assess effects of increasing dietary omega-3, omega-6 or mixed total PUFA on key musculoskeletal outcomes and functional status in adults aged 40 years or older. The study included 28 RCTs (31 comparisons, 7288 participants), of which six were at low summary risk of bias. Twenty-three studies reported on the effects of increasing omega-3 fatty acids, but effects were unclear (as the evidence was of very low quality) for fracture incidence, total proximal femur BMD and skeletal muscle mass. Low or very low-quality data suggested that increasing omega-3 may increase lumbar spine and femoral neck BMD but has little or no effect on total bone mass or measures of functional status. A few small trials suggested increases in physical performance and osteocalcin with increased omega-3 but data were of limited quality. The single eligible study on omega-6 did not report on any primary outcomes, and was not at low summary risk of bias. As far as it could be interpreted, this study suggested little or no effect on arm and leg muscle strength of omega-6. Three RCTs (4 comparisons) assessed effects of increasing mixed total PUFA and none were at low summary risk of bias. None reported on fracture incidence, total bone mass or measures of functional status. The existing data suggested that increasing total PUFA may have little or no effect on BMD (when effects at different sites were combined) or fat-free mass. Data on secondary outcomes were very limited but suggested reductions in leg extensor power, C1NP, NTX/CR, CTX and urinary hydroxyproline, and a small increase in parathyroid hormone with more PUFA. There was considerable heterogeneity in populations studied and doses of fatty acids supplemented.
Despite the limitations of this study due to the lack of comprehensive evidence from trials with low risk of bias, thus limiting the conclusions from our study the importance of PUFA on musculoskeletal heath and outcomes deserves further research. In conclusion, the study found low-quality evidence that omega-3 may increase BMD by a small amount, but there were no other clear effects of omega-3 or total PUFA on skeletal muscle, bone or functional outcomes. Evidence of the effects of omega-6 supplementation on bone or skeletal muscle outcomes was insufficient to warrant any conclusions. Further trials assessing effects of omega-3, omega-6 and mixed PUFA on musculoskeletal outcomes are warranted, but only if the trials are methodologically strong (at low summary risk of bias) and appropriately powered.