Implications of dietary α-linolenic acid in bone health.
Recent evidence implies the benefit of ω-3 polyunsaturated fatty acids in bone health. Although eicosapentaenoic acid and docosahexaenoic acid, present in fish oil, have been extensively researched, much less is known about the influence of α-linolenic acid (ALA; present in flaxseeds), a metabolic precursor of eicosapentaenoic acid and docosahexaenoic acid, 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.
Kim Y, Ilich JZ
Can manipulation of the ratios of essential fatty acids slow the rapid rate of postmenopausal bone loss?
The rapid rate of postmenopausal bone loss is mediated by the inflammatory cytokines interleukin-1, interleukin-6, and tumor necrosis factor alpha. Dietary supplementation with fish oil, flaxseeds, and flaxseed oil in animals and healthy humans significantly reduces cytokine production while concomitantly increasing calcium absorption, bone calcium, and bone density. Possibilities may exist for the therapeutic use of the omega-3 fatty acids, as supplements or in the diet, to blunt the increase of the inflammatory bone resorbing cytokines produced in the early postmenopausal years, in order to slow the rapid rate of postmenopausal bone loss. Evidence also points to the possible benefit of gamma-linolenic acid in preserving bone density.
Altern Med Rev Feb 2001
PMID: 11207457 | Free Full Text
An increase in dietary n-3 fatty acids decreases a marker of bone resorption in humans.
Human, animal, and in vitro research indicates a beneficial effect of appropriate amounts of omega-3 (n-3) polyunsaturated fatty acids (PUFA) on bone health. This is the first controlled feeding study in humans to evaluate the effect of dietary plant-derived n-3 PUFA on bone turnover, assessed by serum concentrations of N-telopeptides (NTx) and bone-specific alkaline phosphatase (BSAP). Subjects (n = 23) consumed each diet for 6 weeks in a randomized, 3-period crossover design: 1) Average American Diet (AAD; [34% total fat, 13% saturated fatty acids (SFA), 13% monounsaturated fatty acids (MUFA), 9% PUFA (7.7% LA, 0.8% ALA)]), 2) Linoleic Acid Diet (LA; [37% total fat, 9% SFA, 12% MUFA, 16% PUFA (12.6% LA, 3.6% ALA)]), and 3) alpha-Linolenic Acid Diet (ALA; [38% total fat, 8% SFA, 12% MUFA, 17% PUFA (10.5% LA, 6.5% ALA)]). Walnuts and flaxseed oil were the predominant sources of ALA. NTx levels were significantly lower following the ALA diet (13.20 +/- 1.21 nM BCE), relative to the AAD (15.59 +/- 1.21 nM BCE) (p < 0.05). Mean NTx level following the LA diet was 13.80 +/- 1.21 nM BCE. There was no change in levels of BSAP across the three diets. Concentrations of NTx were positively correlated with the pro-inflammatory cytokine TNFalpha for all three diets. The results indicate that plant sources of dietary n-3 PUFA may have a protective effect on bone metabolism via a decrease in bone resorption in the presence of consistent levels of bone formation.
Griel AE, Kris-Etherton PM, Hilpert KF, Zhao G…
Nutr J 2007
PMID: 17227589 | Free Full Text