6.3  n-3 PUFAs effects in humans
In healthy subjects, different daily doses of EPA and DHA up 1800 mg, administered up to 5 months, showed no significant effects on the CPR, IL-6, and TNF-α (Asztalos et al., 2016; Flock et al., 2014; Muldoon et al., 2016). A comparable conclusion was drawn by other authors. According to Rangel-Huerta's meta-analysis, consumption of 900 mg–2000 mg n-3 PUFAs does not change inflammatory biomarkers in healthy subjects (Rangel-Huerta et al., 2012). On the other hand, doses between 1250 and 2400 mg n-3 PUFA for 4 months lowered inflammation in sedentary and overweight middle-aged and older adults (Kiecolt-Glaser et al., 2012). Lp-PLA2, another anti-inflammatory marker was significantly reduced by a high dose of EPA (1800 mg) but not by DHA (Asztalos et al., 2016). Interestingly, only DHA modified the lipid profile by decreasing postprandial triglyceride concentrations and significantly increasing low-density lipoprotein cholesterol, with no significant changes in inflammatory biomarkers (Asztalos et al., 2016). In elderly subjects, daily supplementation with 2500 mg EPA and DHA, for 8 weeks, significantly reduced the plasma levels of fatty acids, IL-1β, IL-6, and TNF-α (Tan et al., 2018). Similarly, in obese patients who received different doses of combined n-3 PUFAs (380–1290 mg DHA and 360–460 mg EPA) for 2–3 months, the intervention reduced the expression of proinflammatory genes in adipocytes and systemic inflammatory markers sVCAM-1, CRP, IL-6, and TNF-α (Itariu et al., 2012; Polus et al., 2016). Furthermore, other relevant metabolic findings connected with n-3 PUFA treatment were reported, such as decreasing fasting triglycerides and insulin (Allaire et al., 2016; Polus et al., 2016) or decreasing fasting blood glucose in obese diabetics (Ellulu et al., 2016). Partially, these results are in line with the modest reduction in waist circumference and body-weight found in a meta-analysis (Bender et al., 2014). The authors indicated that the effect regarding waist circumference produced by fish intake or fish oil supplementation and might be greater in men than in women. The beneficial effect in overweight and obese adults concerning waist circumference and triglyceridemia was confirmed by two other meta-analyses (Du et al., 2015; Zhang et al., 2017).
As most of the cited trials utilize a mixture of DHA and EPA which may mask the effects of each compound, the individual effects of DHA or EPA in obese patients were also investigated, but the results were inconclusive. A significant reduction in serum IL-18 and adiponectin with DHA than with EPA was observed in one study (Allaire et al., 2016), while no differences between DHA and EPA in the expression of pro-inflammatory genes were observed in another study (Vors et al., 2017).
In patients with impaired glucose metabolism and T2DM in almost all studies, none of the combined EPA and DHA doses had any effect on IL-6, IL-1β, CRP, VCAM, and sICAM (Clark et al., 2016; Mocking et al., 2012; Sawada et al., 2016). Further, no effects on glycated haemoglobin (HbA1c) (Sawada et al., 2016; Wong et al., 2010), insulin (Clark et al., 2016) or lipid profile (Veleba et al., 2015) were found. Only Veleba et al. (2015), observed that HbA1c decreased significantly, and fasting blood glucose increased after n-3 PUFAs treatment for 24 weeks, but no other key findings. An overview of the most recent human studies where the inflammatory biomarkers as a result of PUFAs treatments, were assessed as the main outcome, is summarized in Table 6 .
Table 6 Clinical effects induced by PUFAs.
Intervention (n) Main anti-inflammatory findings Other relevant findings References
Healthy subjects
4-month intervention:➢ 1.5 g fish oil (1042.5 mg EPA and 174 DHA daily)
➢ 2.5 g fish oil (2085 mg EPA and 348 mg DHA daily)
➢ placebo 138 ↓TNF-α and ↓ IL-6 for both low and high dose groups ↓ n-6:n-3 ratio for both low and high dose groups Kiecolt-Glaser et al. (2012)
6-week intervention:➢ 600 mg EPA/day
➢ 1800 mg EPA/day
➢ 600 mg DHA/day
➢ placebo 121 No effect on hsCRP, TNF-α, IL-6, VCAM-1, ICAM-1 and fibrinogen Only High dose EPA ↓ Lp-PLA2;DHA: ↓ TG; ↑ LDLNo effect of low dose EPA Asztalos et al. (2016)
18-week intervention:1000 mg EPA + 400 mg DHA/day vs. placebo 261 No effect on serum CRP and IL-6 – Muldoon et al. (2016)
5-month intervention:➢ 300 mg EPA + DHA/day
➢ 600 mg EPA + DHA/day
➢ 900 mg EPA + DHA/day
➢ 1800 mg EPA + DHA/day
➢ placebo 125 No significant effect on IL-6 or CPR;Marginal effect on TNF-α observed at the highest dose (1800 mg) Higher RBC DHA was associated with lower TNF-α concentrations. Flock et al. (2014)
8-week intervention:2500 mg EPA + DHA/day vs. placebo 35 ↓IL-6, IL-1β and TNFα – Tan et al. (2018)
Obese patients
2-month intervention:➢ 460 mg EPA and 380 mg DHA/day
➢ control (butter fat) 55 ↓IL-6↓ inflammatory gene expression in adipose tissue↑release of anti-inflammatory eicosanoids in adipose tissue ↓TG Itariu et al. (2012)
3-month intervention: 360 mg EPA and 1290 mg DHA/day vs. placebo 59 ↓ VCAM-1; ↓ PECAM-1; ↓ hsCRP No effect on IL-6 ↓ TG; ↓insulin.No effect on TC, HDL, LDL, NEFA, FBG Polus et al. (2016)
10-week intervention:➢ 2700 mg EPA/day
➢ 2700 mg DHA/day
➢ placebo 154 ↓ IL-18 and ↑ adiponectin (DHA > EPA)No difference between EPA and DHA regarding effect on CRP, IL-6, TNFα ↓ TG; ↑ HDL (DHA > EPA)↑ LDL by DHA only in men Allaire et al. (2016)
10-week intervention:➢ 2700 mg EPA/day
➢ 2700 mg DHA/day
➢ control (corn oil) 154 EPA: ↑TRAF3 and PPARα expressionDHA: ↑ PPARα and TNFα expression both ↓CD14 expression No significant difference between EPA and DHA. Vors et al. (2017)
12-week intervention:➢ LSM + 600 mg EPA + DHA/day
➢ LSM
➢ placebo 29 LSM & n-3 PUFA ↑ adiponectin in comparison to LSMNo effect on IL6 No effect on leptin, LIF, follistatin, BDNF, and fasting triacylglycerol Sedláček et al. (2018)
Hypertensive and/or diabetic obese patients
8-week intervention:300 mg EPA + 200 mg DHA/day vs. control 64 ↓CRP ↓ FBG; ↓TG Ellulu et al. (2016)
Impaired glucose metabolism patients
6-month intervention:1800 mg EPA/day vs. placebo 107 ↓ CRP but similar effects in placebo ↑ HDL and ↓fasting TG; No effect on HbA1c and FBG Sawada et al. (2016)
9-month intervention:2388 mg EPA +1530 mg DHA/day vs placebo 36 No effect in IL-1B, IL-6, hsCRP, ICAM and VCAM No effect on FBG, insulin, HOMA-IR. Clark et al. (2016)
Type 2 diabetes mellitus
12-week intervention: 4000 mg (42% EPA + 25%DHA)/day vs. placebo 91 No significant effect on CPR ↓ TG; No effect on LDL, HDL, HbA1c Wong et al. (2010)
12-week intervention: 900 mg EPA/day vs. placebo 24 No effect on CRP, IL-6 and TNFα ↑ HDL and ↑ total cholesterol Mocking et al. (2012)
8-week intervention: 2700 mg EPA + DHA/day 84 ↓ IL-2 and ↓ TNFαNo effect on CRP None tested Malekshahi Moghadam et al. (2012)
12-weeks intervention:➢ 1000 mg EPA/day
➢ 1000 mg DHA/day
➢ placebo 60 No effect on serum CRP and MDA No effect on body weight, BMI or fat mass Azizi-Soleiman et al. (2013)
24-week intervention:➢ 2800 mg EPA + DHA + 15 mg pioglitazone/day
➢ 2800 mg EPA + DHA + placebo/day
➢ 5 mg pioglitazone/day
➢ placebo 60 No effect on SOD, TBARS, GSSG/GSH ↑ HbA1c; ↑FBGNo effect on TG, TC, HDL, LDL, NEFA, Leptin, Adiponectin Veleba et al. (2015)
3-month intervention: 1000 mg EPA + 1000 mg DHA/day vs. placebo 74 No effect on hsCRP, IL-6, TNF-α, ICAM-1, VCAM-1 No effect on insulin, HbA1c, adiponectin, leptin, and lipid levels Poreba et al. (2017)
Metabolic syndrome
90-day intervention:➢ 1800 mg EPA+ 1200 mg DHA + 10 mL extra virgin oil/day
➢ 1800 mg EPA + 1200 mg DHA + placebo/day
➢ 10 mL extra virgin oil/day
➢ placebo 102 No effect on CPR No effect on TG, TC, HDL, LDL, FBG, insulin, HOMA-IR Venturini et al. (2015)
Inflammatory bowel disease
8-week intervention: 3400–3600 mg n-3 PUFA (as salmon)/day 12 ↓ CPR, ↑ anti-inflammatory fatty acid indexNo effect TNF- α, MDA ↑ n-3 PUFAs,↑ n-3/n-6 ratio in plasma and rectal biopsies; No effect on the fecal calprotectine Grimstad et al. (2011)
90-day intervention: 2000 mg EPA/day 20 ↑ IL-10 expression; HES1, SOCS3, and KLF4 ↓ fecal calprotectinePartially redressed microbiota composition Prossomariti et al. (2017)
6-month intervention: 1000 mg EPA/day vs.placebo 60 No effect on CPR ↓ fecal calprotectine Scaioli et al. (2018)
EPA – Eicosapentaenoic Acid; DHA – Docosahexaenoic Acid; PG – Prostaglandins; LTB – Leukotriene; TNF-α – Tumour Necrosis Factor alpha; IL – Interleukin; CRP – C-Reactive Protein; ICAM – Intercellular Adhesion Molecule; VCAM – Vascular Cell Adhesion molecule; hsCRP – high sensitive C reactive protein; IL1RN – interleukin-1 receptor antagonist protein; LSM – lifestyle modification; NF-κB – nuclear factor-kappa B); PPAR – peroxisome proliferator-activated receptor; TRAF3 – TNF Receptor Associated Factor 3; Lp-PLA2 – lipoprotein-associated phospholipase A2; PECAM – platelet and endothelial cell adhesion molecule; COX – cyclooxygenase; LOX – lypoooxigenase; TBARS –thiobarbituric acid substances; SOD – superoxide dismutase; GSH – glutathione peroxidase; MDA – malonyldialdehyde; HOMA-IR – homeostasis model assessment of insulin resistance index; HES1 – transcription factor HES1; SOCCS3 – suppressor of cytokine signaling 3; KLF4 – Kruppel-like factor 4; HbA1c – Glycated haemoglobin; RBC – red blood cell; BDNF – Brain-derived neurotrophic factor; CD14 – cluster of differentiation 14; NEFA – Non-esterified fatty acids; TC – total cholesterol; TG – Triglycerides; LDL – low-density lipoproteins; HDL – high-density lipoproteins; FBG – fasting blood glucose; LIF – leukocyte inhibitory factor.