Key Findings:
ALA conversion to EPA, DPAn-3 and DHA in tracer studies has been observed in nearly all humans studied from birth through late middle age and in both males and females. The majority of evidence from isotopic tracer studies indicates the conversion of ALA to DHA is about 1% in infants, and may be lower in adults. These ‘‘conversion rates’’ must be viewed as markers of flux through this metabolic pathway but must not be assumed to represent a net change in mass. ALA appears to contribute little to circulating DHA when the diet has high LA levels. The conversion of ALA to EPA and DHA is decreased by high dietary ratios of LA/ALA. Research indicates that n-3 LCPUFA status can be improved by increasing their intake or by decreasing LA intake, with both being most effective.
ABSTRACT:
Blood levels of polyunsaturated fatty acids (PUFA) are considered biomarkers of status. Alpha-linolenic acid, ALA, the plant omega-3, is the dietary precursor for the long-chain omega-3 PUFA eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA), and docosahexaenoic acid (DHA). Studies in normal healthy adults consuming western diets, which are rich in linoleic acid (LA), show that supplemental ALA raises EPA and DPA status in the blood and in breast milk. However, ALA or EPA dietary supplements have little effect on blood or breast milk DHA levels, whereas consumption of preformed DHA is effective in raising blood DHA levels. Addition of ALA to the diets of formula-fed infants does raise DHA, but no level of ALA tested raises DHA to levels achievable with preformed DHA at intakes similar to typical human milk DHA supply. The DHA status of infants and adults consuming preformed DHA in their diets is, on average, greater than that of people who do not consume DHA. With no other changes in diet, improvement of blood DHA status can be achieved with dietary supplements of preformed DHA, but not with supplementation of ALA, EPA, or other precursors. (Author’s abstract)
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