In the body, alpha-linolenic acid can function as a precursor for the production of the long-chain omega-3 fatty acids EPA and DHA. However, these conversions are limited; they have been estimated to occur at rates of <8% and <4% for EPA and DHA, respectively.[1] There are many factors that can impact the efficiency of this conversion, such as sex, genetic polymorphisms, disease states, and habitual fatty acid consumption.[1][2] For example, premenopausal women can convert alpha-linolenic acid to EPA and DHA at a significantly greater rate due to higher levels of estrogen, which can upregulate the expression of the enzymes required for the conversion.[1][3] This likely relates to the importance of DHA during fetal development and lactation. Another contributing factor may be the level of omega-6 fatty acids consumed.
Both alpha-linolenic acid and linoleic acid — an essential omega-6 fatty acid — compete for the same enzymes that convert them into longer chain fatty acids. Restricting linoleic acid while increasing alpha-linolenic acid intake has been shown to increase levels of EPA and sometimes DHA in clinical trials, although the effect is small.[4]
Lastly, the dose of alpha-linolenic acid is important. For example, a clinical trial found that 30 grams daily of ground flaxseed was sufficient to raise levels of EPA in the blood, but 10 grams daily was not.[5]