Nutrients. , 2022., Jan 12;14(2):301. doi: 10.3390/nu14020301

Dietary Alpha-Linolenic Acid Supports High Retinal DHA Levels.

Sinclair AJ Guo XF Abedin L


The retina requires docosahexaenoic acid (DHA) for optimal function. Alpha-linolenic acid (ALA) and DHA are dietary sources of retinal DHA. This research investigated optimizing retinal DHA using dietary ALA. Previous research identified 19% DHA in retinal phospholipids was associated with optimal retinal function in guinea pigs. Pregnant guinea pigs were fed dietary ALA from 2.8% to 17.3% of diet fatty acids, at a constant level of linoleic acid (LA) of 18% for the last one third of gestation and retinal DHA levels were assessed in 3-week-old offspring maintained on the same diets as their mothers. Retinal DHA increased in a linear fashion with the maximum on the diet with LA:ALA of 1:1. Feeding diets with LA:ALA of 1:1 during pregnancy and assessing retinal DHA in 3-week-old offspring was associated with optimized retinal DHA levels. We speculate that the current intakes of ALA in human diets, especially in relation to LA intakes, are inadequate to support high DHA levels in the retina.

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Key Points

It is not known is the minimum amount of dietary ALA to reach a retinal DHA value within the optimal retinal function range (19% DHA).  This study is the first to determine the amount of dietary ALA required to maintain retina PL DHA in the optimal retinal DHA range. To achieve this, pregnant guinea pigs were fed diets with increasing amounts of ALA at a constant LA level and their offspring were examined in early postnatal life (3-weeks of age). In the guinea pig, myelination commences in utero as it does in humans. It was shown that at 3-weeks of age, ALA at 17.3% of diet fatty acids in a 1.1 ratio with LA achieved a retinal DHA value within the optimum range. The novelty of this research is that it is the first to determine the amount of dietary ALA required to maintain retina PL DHA in the optimal retinal DHA range. It was found that a diet with LA:ALA in the range 1:1 optimized retinal DHA levels.

DHA is highly concentrated in neural membranes as well as in the photoreceptor cells of the retina and depletion of ALA in the diet leads to deficiencies of DHA in both tissues, as shown here. Since many studies have reported significant alterations in neural function associated with depletion of DHA in neural membranes as a result of the animals being fed ALA-deficient diets, the present work is also relevant to the brain. The relevance of the present data to vegans is that the retinal PUFA showed evidence of significant biochemical n-3 (DHA) deficiency in 3-week-old guinea pigs with dietary LA:ALA of 2.75:1. In vegan and vegetarian diets, the LA:ALA is unlikely to be less than 10:1. Therefore, if these studies can be translated to vegans and vegetarians who do not consume sources of EPA and DHA, it suggests these groups do not have a sufficiently high ALA intake to optimize their retinal (and presumably brain) DHA levels. The only practical way for vegans and vegetarians to optimize their diet for optimal retinal DHA values is to consume suitable sources of DHA, as it is unlikely that they could reach a dietary LA:ALA ratio of 1:1.