University of Toronto, Department of Nutritional Sciences, Canada.
University of Toronto, Department of Nutritional Sciences, Canada.
Prog Lipid Res. 2015 Jul;59:54-66. doi: 10.1016/j.plipres.2015.04.002. Epub 2015 Apr 25.
Docosahexaenoic acid (DHA) is important for brain function, and can be obtained directly from the diet or synthesized in the body from α-linolenic acid (ALA). Debate exists as to whether DHA synthesized from ALA can provide sufficient DHA for the adult brain, as measures of DHA synthesis from ingested ALA are typically <1% of the oral ALA dose. However, the primary fate of orally administered ALA is β-oxidation and long-term storage in adipose tissue, suggesting that DHA synthesis measures involving oral ALA tracer ingestion may underestimate total DHA synthesis. There is also evidence that DHA synthesized from ALA can meet brain DHA requirements, as animals fed ALA-only diets have brain DHA concentrations similar to DHA-fed animals, and the brain DHA requirement is estimated to be only 2.4-3.8 mg/day in humans. This review summarizes evidence that DHA synthesis from ALA can provide sufficient DHA for the adult brain by examining work in humans and animals involving estimates of DHA synthesis and brain DHA requirements. Also, an update on methods to measure DHA synthesis in humans is presented highlighting a novel approach involving steady-state infusion of stable isotope-labeled ALA that bypasses several limitations of oral tracer ingestion. It is shown that this method produces estimates of DHA synthesis that are at least 3-fold higher than brain uptake rates in rats.
二十二碳六烯酸（DHA）对大脑功能很重要，可以直接从饮食中获得，也可以由α-亚麻酸（ALA）在体内合成。目前仍存在争议，即由 ALA 合成的 DHA 是否能为成人大脑提供足够的 DHA，因为从摄入的 ALA 测量 DHA 合成通常<1%口服 ALA 剂量。然而，口服 ALA 的主要命运是β-氧化和长期储存在脂肪组织中，这表明涉及口服 ALA 示踪剂摄入的 DHA 合成测量可能低估了总 DHA 合成。还有证据表明，由 ALA 合成的 DHA 可以满足大脑对 DHA 的需求，因为仅用 ALA 喂养的动物的大脑 DHA 浓度与用 DHA 喂养的动物相似，并且人类大脑 DHA 的需求量估计仅为 2.4-3.8mg/天。本综述通过检查人类和动物中涉及 DHA 合成和大脑 DHA 需求估计的工作，总结了由 ALA 合成的 DHA 可为成人大脑提供足够 DHA 的证据。还介绍了一种更新的人类 DHA 合成测量方法，重点介绍了一种涉及稳定同位素标记的 ALA 稳态输注的新方法，该方法绕过了口服示踪剂摄入的几个限制。结果表明，该方法产生的 DHA 合成估计值至少比大鼠大脑摄取率高 3 倍。
