Journal Name:
Clinical Chemistry
Article Title:
Incorporation and Clearance of Omega-3 Fatty Acids in Erythrocyte Membranes and Plasma Phospholipids
Date Written:
2006
Volume:
52
Number:
12
Page:
2265
Author(s):
Cao, J.; Schwichtenberg, K.A.; Hanson, N,Q.; Tsai, M.Y.
Article:
The sum of eicosapentaenoic acid (EPA, 20:5n3) and docosahexaenoic acid (DHA, 22:6 n3) in erythrocyte membranes, termed the omega-3 index, can indicate suboptimal intake of omega-3 fatty acids, a risk factor for cardiovascular disease (CVD). If laboratories are to offer omega-3 indices as a risk factor for CVD, more studies are needed to establish the quantitative and temporal relationship between intake of omega-3 fatty acids, incorporation into erythrocyte membranes, and the rate at which these fatty acids diminish from erythrocyte membranes over time when supplementation is discontinued or interrupted. To study the effects of fatty acid supplementation, this study investigated the rate of incorporation and clearance of these fatty acids in erythrocyte membranes and plasma after intake of supplements.
Twenty study participants received supplementation with either fish oil (1296 mg EPA + 864 mg DHA/day) or flaxseed oil (3510 mg alpha-linolenic acid + 900 mg linoleic acid/day) for 8 weeks. Erythrocyte membrane and plasma samples at weeks 0, 4, 8, 10, 12, 14, 16, and 24 and extracted and analyzed fatty acids by gas chromatography. After 8 weeks of fish oil supplementation, erythrocyte membrane EPA and DHA increased 300% and 42%, respectively. The mean erythrocyte omega-3 index reached a near optimal value of 7.8%, and remained relatively high until week 12. EPA and DHA showed greater increases and more rapid washout period decreases in plasma phospholipids than in erythrocyte membranes. ALA from flaxseed oil supplementation increased erythrocyte membrane EPA to 133% and docosapentaenoic acid (DPA, 22:5 n3) to 120% of baseline, but DHA was unchanged. In plasma phospholipids, EPA, DPA, and DHA showed a slight but statistically insignificant increase.
The mean omega-3 index in the 9 participants increased from 4.3% to 7.8% in erythrocyte membranes. The data shows that for each gram of EPA ingested, there was a mean increase of 1.4% after 8 weeks (range 1.0%–1.8%). A mean increase of 1.9% per gram of DHA in 8 weeks was noted. *EPA fell to pre-supplementation concentrations 2 weeks post supplementation. The decline in DHA concentration was more gradual, such that 54% of the increase in mean DHA concentration was retained 2 weeks post supplementation, and 25% was retained 6 weeks post supplementation. Thus erythrocyte membrane is a better index for monitoring long-term intake of omega-3 fatty acids, whereas plasma phospholipids are more sensitive to short-term changes in the intake of omega-3 fatty acids and may thus be more useful in monitoring the compliance of individuals in intervention studies with fish oil supplementation.
The current study shows that intake of ALA had little effect on EPA and DHA concentrations in the blood. For each gram of ALA supplement, the mean erythrocyte membrane EPA and DHA concentrations increased 0.1% and _0.1% (0.03%) respectively. Supplementation with flaxseed oil resulted in a significant increase of DPA concentrations in erythrocyte membranes, comparable to that in the fish oil group. The rapid conversion between EPA and DPA indicates the possibility that DPA can be a potential storage form for EPA.
The mechanism by which ALA exerts its cardioprotective effects may be 2-fold. First, ALA may have protective effects on cardiac arrhythmia, inflammation, and thrombosis. In addition, ALA supplementation enriches EPA and DPA composition in erythrocyte membranes. Although EPA concentration is only mildly increased, the increase in DPA in erythrocyte membranes may act to sustain a constant supply of EPA and its beneficial effects. Erythrocyte membrane EPA+DHA increases during relatively short intervals in response to supplementation at rates related to amount of supplementation. ALA consumption yields significant increase in EPA and DPA but not DHA. These results may be useful to establish appropriate dosage for omega-3 fatty acid supplementation.
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