Summary
Sarcopenia, the progressive loss of muscle mass and strength, is associated with aging and inflammation. Crucially, omega-3 fatty acids such as DHA are implicated in muscle health and function. Accordingly, studies have shown that omega-3 fatty acids can have positive effects in the context of sarcopenia, by promoting gain in muscle mass and function.
 
Introduction
Sarcopenia is a progressive and often age-related condition characterized by a loss of skeletal muscle mass, strength, and physical function. It typically begins in the fourth or fifth decade of life, accelerating after the age of 60. Sarcopenia can also arise as a result of poor nutrition, prolonged physical inactivity and through diseases such as cancer or chronic kidney disease. The sarcopenia-related effects on muscle mass and strength contribute to frailty and is associated with adverse outcomes including impaired mobility, increased risk of falls and fractures, reduced quality of life, longer hospital stays, and higher all-cause mortality.

Strikingly, research shows that Omega-3 fatty acids such as EPA and DHA have a positive effect on skeletal muscle mass and function. The incorporation of EPA and DHA in the membranes of muscle cells increases their rates of muscle protein generation, together with causing a decrease of factors that are involved in the breakdown of muscle proteins. Clinical trials have shown that supplementation  with EPA and DHA has positive effects on muscle health and function in non-sarcopenic young adults. Accordingly, scientific interest in these findings have led to the development of clinical trials investigating the effects of DHA and EPA in sarcopenia, with promising results. Moreover, inflammation is thought to play a central role in the development and progression of sarcopenia; the anti-inflammatory properties of DHA and EPA may therefore have beneficial effects in this context as well. All of these theories have been investigated in multiple studies, including clinical trials, discussed below.
 
Research findings
In a clinical trial by Heileson and fellow scientists, the effects of EPA and DHA supplementation in combination with resistance exercise training were investigated in healthy adults between 18 and 40 years of age (Heileson et al., 2023). During a 10 week resistance exercise training regime, 21 men and women were given either a daily placebo or 2.2g EPA and 1.6g DHA per day. Muscle strength was assessed by the maximum barbell back squat and bench press weight (both absolute weight and relative to body mass) at the beginning and end of the 10-week supplementation period. The authors reported that the supplementation group showed a greater improvement in absolute and relative maximum barbell back squat and bench press weight compared to the placebo group after 10 weeks. Whereas the placebo group showed an improvement of 9.7% in absolute strength and 7.3% relative strength, the supplementation group showed an improvement of 17.7% in absolute strength and 17.6% in relative strength. The improvement in strength measured in the control group is to be expected, as this is a typical effect of resistance exercise training. Nevertheless, the finding of greater relative improvement in the supplementation group shows that EPA and DHA can enhance the effects of resistance exercise training on muscle strength.
 
The effects of EPA and DHA supplementation on enhancing muscle strength in elderly women (64± 1.4 years of age) has been published in an interesting study by Rodacki and colleagues (Rodacki et al., 2012). Forty-five women were equally divided into 3 groups that all followed a 90-day strength training regime. The first group received no supplementation, the second group received 0.4g EPA and 0.3g DHA per day during the 90 day training regime, the third group received 0.4g EPA and 0.3g DHA per day from the 60 days leading up to the training regime and during the 90 days of strength training. The muscle strength and functional capacity were measured at the beginning and end of the training regime. The groups logically showed no difference in these measurements at the beginning of the study. After the training regime, all groups showed improvements in muscle strength and functional capacity, though both the supplementation groups showed a greater increase in these factors than the non-supplemented group. There was no difference between the two supplementation groups, likely because the supplementation caused participants to reach a plateau of circulating DHA and EPA which could not be further enhanced by starting the supplementation period before the training regime. Taken together, this study highlights the synergetic effect of Omega-3 fatty acids DHA and EPA on exercise-induced increases in muscle strength and capacity.
 
In a clinical trial with 102 elderly men and women without sarcopenia, Alkhedhairi and colleagues researched the effects of DHA and EPA supplementation on muscle function and size (Alkhedhairi et al., 2022). For a period of 6 months, participants received either a daily placebo (control group, 45 participants) or 772mg EPA and 384mg DHA (supplementation group, 57 participants). Knee extensor strength, grip strength and skeletal muscle thickness were assessed at the beginning of the study, 6 weeks after the study start and at the end of the supplementation period. In contrast to other studies, participants in this study were not given an exercise regime, instead exercising for less then one hour per week. Compared to the control group, the supplementation group showed greater increases in knee extensor strength, grip strength and skeletal muscle thickness at the 6-month timepoint. These robust findings show how DHA and EPA can contribute to healthy muscle mass and function even without an exercise regime.
 
Kim and fellow scientists investigated the relationship between circulating DHA levels and muscle mass and strength in elderly men with sarcopenia (Kim et al., 2023). The study with 142 elderly men consisted of persons with sarcopenia and age-matched controls. Blood plasma samples were taken to assess levels of Omega-3 fatty acids and their metabolites; these were plotted against measurements of muscle mass and function. Interestingly, the authors found that  docosahexaenoic acid ethanolamide, a metabolite of DHA, was lower in the plasma of sarcopenic men compared to age-matched controls. Moreover, higher levels of this metabolite correlated with higher skeletal muscle mass index scores, as well as hand grip strength. The authors concluded that DHA and its metabolization in the body likely serves as a beneficial factor in the face of sarcopenia in elderly men.
 
In a small clinical trial by Smith and colleagues, the effects of EPA+DHA supplementation in relation to muscle protein synthesis was investigated in healthy adults aged  71 ±2 years (Smith et al., 2011). Participants were given either a daily placebo (8 individuals, control group) or 1.9g EPA and 1.5g DHA (8 individuals, supplementation group) for a period of 8 weeks. Muscle tissue samples were taken at the beginning and end of the supplementation period to establish connections between EPA, DHA and muscle protein synthesis rate.  It was discovered that compared to the control group, participants receiving the EPA and DHA supplementation had higher levels of muscle protein synthesis; this supports the findings of others who report a positive effect of these Omega-3 fatty acids on muscle mass.  
In a follow up trial, Smith and colleagues investigated the effects of this supplementation regime for a period of 6 months in adults aged 60-85 years (Smith et al., 2015) on parameters used to assess sarcopenia. Participants received either a placebo (20 individuals, control group) or the aforementioned supplementation regime (40 individuals, treatment group) for a period of 6 months. At the beginning and end of this study, participants undertook assessments of thigh muscle volume, hand grip strength and one-repetition maximum lower- and upper-body strength. The authors reported that compared with the control group at 6 months, the supplementation group showed an increase in all of the abovenamed parameters. As these are often used to assess sarcopenia severity, the results of this study support the positive role that EPA and DHA can have in muscle health parameters negatively affected by sarcopenia.
 
Conclusion
Sarcopenia negatively affects quality of life via the loss of muscle mass and strength, also referred to as frailty. Though this condition is commonly associated with ageing, it can also arise in the face of prolonged inactivity, disease or malnutrition, amongst others. Studies have shown that DHA and EPA supplementation can enhance the effects of exercise training on muscle strength and function. The strength that this synergetic effect may have on sarcopenia however likely depends on the severity of sarcopenia, as well as its main causing factor.  Strikingly, even in non-exercising elderly individuals, supplementation with EPA and DHA can improve muscle health and function parameters used to assess sarcopenia. The overall consensus is that supplementation with these Omega-3 fatty acids is well tolerated and contributes to muscle health and function. Taken together, observational studies and clinical trials support the positive effects of DHA in the context of sarcopenia; individuals with this condition may therefore consider DHA and EPA supplements to ensure adequate intake of these Omega-3 fatty acids.
 
References
Alkhedhairi, S. A., Aba Alkhayl, F. F., Ismail, A. D., Rozendaal, A., German, M., MacLean, B., Johnston, L., Miller, A. A., Hunter, A. M., Macgregor, L. J., Combet, E., Quinn, T. J., & Gray, S. R. (2022). The effect of krill oil supplementation on skeletal muscle function and size in older adults: A randomised controlled trial. Clinical Nutrition (Edinburgh, Scotland), 41(6), 1228–1235. https://doi.org/10.1016/j.clnu.2022.04.007

Heileson, J. L., Machek, S. B., Harris, D. R., Tomek, S., de Souza, L. C., Kieffer, A. J., Barringer, N. D., Gallucci, A., Forsse, J. S., & Funderburk, L. K. (2023). The effect of fish oil supplementation on resistance training-induced adaptations. Journal of the International Society of Sports Nutrition, 20(1), 2174704. https://doi.org/10.1080/15502783.2023.2174704

Kim, Y. A., Lee, S. H., Koh, J., Kwon, S., Lee, Y., Cho, H. J., Kim, H., Kim, S. J., Lee, J. H., Yoo, H. J., & Seo, J. H. (2023). Fatty acid amides as potential circulating biomarkers for sarcopenia. Journal of Cachexia, Sarcopenia and Muscle, 14(3), 1558–1568. https://doi.org/10.1002/jcsm.13244

Rodacki, C. L., Rodacki, A. L., Pereira, G., Naliwaiko, K., Coelho, I., Pequito, D., & Fernandes, L. C. (2012). Fish-oil supplementation enhances the effects of strength training in elderly women. The American Journal of Clinical Nutrition, 95(2), 428–436. https://doi.org/10.3945/ajcn.111.021915

Smith, G. I., Atherton, P., Reeds, D. N., Mohammed, B. S., Rankin, D., Rennie, M. J., & Mittendorfer, B. (2011). Dietary omega-3 fatty acid supplementation increases the rate of muscle protein synthesis in older adults: A randomized controlled trial. The American Journal of Clinical Nutrition, 93(2), 402–412. https://doi.org/10.3945/ajcn.110.005611

Smith, G. I., Julliand, S., Reeds, D. N., Sinacore, D. R., Klein, S., & Mittendorfer, B. (2015). Fish oil–derived n−3 PUFA therapy increases muscle mass and function in healthy older adults1. The American Journal of Clinical Nutrition, 102(1), 115–122. https://doi.org/10.3945/ajcn.114.105833