Non-dietary factors associated with n-3 long-chain PUFA levels in humans - a systematic literature review

Abstract

Numerous health benefits are attributed to the n-3 long-chain PUFA (n-3 LCPUFA); EPA and DHA. A systematic literature review was conducted to investigate factors, other than diet, that are associated with the n-3 LCPUFA levels. The inclusion criteria were papers written in English, carried out in adult non-pregnant humans, n-3 LCPUFA measured in blood or tissue, data from cross-sectional studies, or baseline data from intervention studies. The search revealed 5076 unique articles of which seventy were included in the qualitative synthesis. Three main groups of factors potentially associated with n-3 LCPUFA levels were identified: (1) unmodifiable factors (sex, genetics, age), (2) modifiable factors (body size, physical activity, alcohol, smoking) and (3) bioavailability factors (chemically bound form of supplements, krill oil v. fish oil, and conversion of plant-derived α-linolenic acid (ALA) to n-3 LCPUFA). Results showed that factors positively associated with n-3 LCPUFA levels were age, female sex (women younger than 50 years), wine consumption and the TAG form. Factors negatively associated with n-3 LCPUFA levels were genetics, BMI (if erythrocyte EPA and DHA levels are <5·6 %) and smoking. The evidence for girth, physical activity and krill oil v. fish oil associated with n-3 LCPUFA levels is inconclusive. There is also evidence that higher ALA consumption leads to increased levels of EPA but not DHA. In conclusion, sex, age, BMI, alcohol consumption, smoking and the form of n-3 LCPUFA are all factors that need to be taken into account in n-3 LCPUFA research.

Keywords: ALA α-linolenic acid; DPA docosapentaenoic acid; FADS fatty acid desaturase; PL phospholipids; SDA stearidonic acid; n-3 LCPUFA n-3 long-chain PUFA; Determinants; Effects; Fatty acid status; Healthy adults; Implications; Measurement; Review studies.

Fig. 1

Flow diagram of systematic literature review search. The flow diagram outlines the identification, screening, eligibility and inclusion process of the systematic literature search. n-3 LCPUFA, n-3 long-chain PUFA.

Fig. 2

Plasma EPA levels and DHA (wt% of total fatty acids) of different age groups from studies reviewed in this systematic literature review. Each line represents a different study (population) and each symbol on a line represents an age group. Full line = significant difference between age groups measured in that study. Broken line = no significant difference between age groups measured in that study. , Plourde et al.^{( 43 )} NS; , Vandal et al.^{( 42 )} NS; , Sfar et al. (women)^{( 54 )}; , Sfar et al. (men)^{( 54 )} NS; , Fortier et al.^{( 40 )} NS; , Dewailly et al.^{( 58 )}; , Dewailly et al.^{( 59 )}; , Rees et al. g1^{( 41 )}; , Rees et al. g2^{( 41 )}; , Rees et al. g3^{( 41 )}; , Rees et al. g4^{( 41 )}; , Kuriki et al.^{( 46 )} NS; , Dewailly et al.^{( 61 )}; , Babin et al.^{( 57 )} NS.

Fig. 3

Erythrocyte EPA levels and DHA (wt% of total fatty acids) of different age groups from studies reviewed in this systematic literature review. Each line represents a different study (population) and each symbol on a line represents an age group. Full line=significant difference between age groups measured in that study. Broken line=no significant difference between age groups measured in that study. , Kawabata et al. ^{( 53 )} (women subjects) NS; , Kawabata et al. ^{( 53 )} (male subjects); , Babin et al. ^{( 57 )} NS; , Walker et al. ^{( 39 )} NS.

Fig. 4

EPA and DHA levels in alcohol abstainers v. wine drinkers. Bar graph presents plasma EPA and DHA (percentage of total fatty acids) for de Lorgeril^{( 74 )} and di Giuseppe^{( 75 )} studies and EPA and DHA concentration in HDL phosphatidylcholines for the Perret study^{( 78 )}. *P<0·05. †DHA intake was approximately 3× lower in subjects who drank >3 drinks per d compared with other subjects. ^a,bBars in the same study with unlike letters have significantly different fatty acid levels. ALA, α-linolenic acid.

Fig. 5

EPA and DHA levels at different alcohol intake. di Giuseppe^{( 75 )} shows EPA and DHA levels for beer and spirit drinkers. Alcohol type was not reported for the four other studies shown in the bar graph. Bar graph presents plasma EPA and DHA (percentage of total fatty acids) for Dewailly^{( 58 , 59 , 61 )} and di Giuseppe^{( 75 )} studies and DHA concentration in HDL phosphatidylcholines for the Alling study^{( 80 )}. ^a,b Bars in the same study with unlike letters are significantly different from each other.

Fig. 6

Mammalian PUFA synthesis pathway showing the n-3 PUFA pathway and the n-6 PUFA pathway, including the enzymes responsible for the elongation and desaturation steps. ELOVL, elongation of very long-chain fatty acid; DPA, docosapentaenoic acid.