Implications of dietary a-linolenic acid in bone health.

Key Findings:

This paper provides a systemic review of the literature and distinguishes between the individual effects of flaxseed oil and flax lignans on bone health. Conclusions included that, in older adults (particularly postmenopausal women), supplementation with flaxseeds or flaxseed oil appears to have a marginal benefit to bone, possibly by inhibiting bone resorption. Both seed and oil improved lipid profiles in plasma, bone, and other tissues by increasing n-3 PUFA and decreasing n-6 PUFA levels in animal models. This subsequently improved bone properties. In animals with secondary osteoporosis due to PKD, IBD, or obesity with insulin resistance, improvements were found in bone strength, BMD, and BMC with both seed and oil. The effect of flax lignans on bone is controversial; however, it seems that younger females are more sensitive to dietary flax lignans. Further studies comparing ALA with EPA and DHA are recommended.

ABSTRACT:

Recent evidence implies the benefit of u-3 polyunsaturated fatty acids in bone health. Although eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), present in fish oil, have been extensively researched, much less is known about the influence of alpha-linolenic acid (ALA; present in flaxseeds), a metabolic precursor of EPA and DHA, on bone. Our objective was to evaluate the published literature and distinguish between the individual effects of flaxseed oil and flax lignans on bone to elucidate the exact role of ALA in skeletal biology. The search was conducted in several databases resulting in 129 articles of which 30 were eligible for inclusion in this review. The studies showed that consumption of whole flaxseeds did not lead to a marked improvement of osteoporotic bones in humans and animals. However, when combined with estrogen therapy, flaxseed supplementation offered an extra benefit to bone in animal models. Similar results were found in studies conducted with flaxseed oil (predominantly ALA), but the favorable role of flaxseed oil was more obvious in various pathologic conditions (kidney disease, obesity with insulin resistance), resulting in improved bone properties. In contrast, despite a marginal estrogenic effect, the consumption of flax lignans resulted in little benefit to bone and the effect was limited to early life of females only in animal models. Based on the available studies, it could be concluded that supplementation with flaxseeds may contribute to some improvement in osteoporotic bone properties but the bone-protective effect may be attributed to ALA, not to the lignan fraction of flaxseeds. (Author’s Abstract)