The study of flax and bone metabolism is a hot new area of emerging research. Phytoestrogens such as lignans may help prevent osteoporosis (1), a disease in which bone mass is low and the risk of bone fractures is high. Flax lignans may have a positive effect on bone in postmenopausal women by enhancing antioxidant activity (2). Free radicals generated in bone tend to cause bone resorption, which increases bone loss (1). A role for flax in blocking the formation of free radicals in bone is plausible, because the main flax lignan secoisolariciresinol diglycoside (SDG) and its mammalian metabolites are strong antioxidants (2). In addition, hormone deficiency is a risk factor for osteoporosis in postmenopausal women. As phytoestrogens, lignans possess both weak estrogenic and antiestrogenic activities and may be a natural alternative for women in preserving bone health (1).
Research in animal models supports a beneficial role for SDG, the mammalian lignan precursor in flaxseed, on the developing bone. In work conducted at the University of Toronto, exposure to SDG purified from flaxseed was assessed during suckling via mother’s milk or continuously to adolescence (postnatal day (PND) 50) or adulthood (PND 132) (3). Offspring were exposed to basal diet (BD) or one of two doses of SDG (50S, 100S) equivalent to that in a 50 or 100 g flaxseed/kg diet during lactation only or through to PND 50 or 132. Compared with BD group, rats exposed to continuous 50S or 100S diet had stronger femurs at PND 50 without changes in BMC. The authors concluded that female rat bone is more sensitive to the estrogen-like action of lignans during early life when endogenous levels of sex hormones are low, but by adulthood the improved bone strength does not persist.
Omega 3 alpha-linolenic acid (ALA) shows a beneficial effect on bone health. A controlled feeding study has been conducted in humans to evaluate the effect of ALA on bone turnover, assessed by serum concentrations of N-telopeptides (NTx) (4). Healthy subjects 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) α-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 (a measure of bone turnover) were significantly lower following the ALA diet relative to the AAD. ALA appears to have protective effects on bone metabolism through reductions in bone resorption in the presence of consistent levels of bone formation. These results suggest that incorporating ALA into the diet may provide health benefits to the skeletal system.
Bone loss is common with aging. In a double-blind crossover study, 38 postmenopausal women, not on hormone replacement therapy, were randomly assigned to flaxseed or sunflower seed diets (5). During two 6-wk periods, subjects were provided with 38 g of either treatment. Flaxseed treatment lowered serum tartrate-resistant acid phosphatase activity (marker of bone resorption), but did not affect serum bone-specific or total alkaline phosphatase activities (markers of bone formation), in comparison with the control group. The urinary excretions of hydroxyproline, another marker of bone resorption, and calcium were decreased following the flaxseed diet. These observations suggest that flaxseed may exert positive effects on bone metabolism by reducing the rate of bone resorption. The investigators speculate that flaxseed may improve bone metabolism by enhancing antioxidant status and decreasing urinary loss of calcium.
The most recent study posted to flaxresearch.com, evaluated the effects of flaxseed flour in femur quality during post-weaning of dam rats (6). The research was designed to mimic bone changes in women during pregnancy and the postpartum period. Such alterations can increase a women’s risk for subsequent development of osteoporosis. After weaning, the rats were divided into control (C, n = 7) and experimental (F, n = 7) groups treated with a diet containing 25 g of flaxseed flour in the lactating period and 15 g in the maintenance period. In biomechanical analysis, the F group showed higher maximum force (+12%), breaking strength (+25%), rigidity (+17%), and femoral head radiodensity (+15%). Ani9mals fed flaxseed also showed lower omega-6 pro-inflammatory arachidonic acid (-44%) and higher ALA (+695%,) and EPA (+160%). Flaxseed feeding resulted in better bone quality, which may be associated with lower serum levels of arachidonic acid and higher EPA, showing an anti-inflammatory profile and increased deposition of organic matrix during the post-weaning period, and may result in prevention of future osteoporosis.
Skeletal health is a lifelong process impacted by environmental factors, including nutrient intake. Flaxseed with its high levels of ALA and lignans appears to be associated with benefits for bone health.
References:
- Arjmandi, BH. The Role of Phytoestrogens in the Prevention and Treatment of Osteoporosis in Ovarian Hormone Deficiency. J Amer College Nutr. (2001), 20,398S.
- Adolphe, JL, Whiting, SJ, Juurlink BHJ, et al. Health effects with consumption of the flax lignan secoisolariciresinol diglucoside. Br J Nutr. (2010), 103, 929–938.
- Ward, WE, Yuan, YV, Cheung, AM and Thompson, LU. Exposure to purified lignan from flaxseed (Linum usitatissimum) alters bone development in female rats. Br J Nutr (2001), 86, 499–505.
- Griel, AE, Penny M Kris-Etherton, PM, Hilpert, KF, et al. An increase in dietary n-3 fatty acids decreases a marker of bone resorption in humans. Nutr J. (2007), 76,2.
- Arjmandi, BH, Shanil Juma, S, Edralin A. Lucas, EA, et al. Flaxseed Supplementation Positively Influences Bone Metabolism in Postmenopausal Women. J Amer Nutra Assoc. (1998), 1(2): 29.
- Ribeiro DC, Pereira AD, de Santana FC, Mancini-Filho J, et al. Incorporation of Flaxseed Flour as a Dietary Source for ALA Increases Bone Density and Strength in Post-Partum Female Rats. Lipids. (2017) Mar 21. doi: 10.1007/s11745-017-4245-2.