Dietary Intakes of Arachidonic Acid and a-Linolenic Acid Are Associated with Reduced Risk of Hip Fracture in Older Adults

PUFA are hypothesized to influence bone health, but longitudinal studies on hip fracture risk are lacking. We examined associations between intakes of PUFA and fish, and hip fracture risk among older adults (n = 904) in the Framingham Osteoporosis Study. Participants (mean age, 75 y at baseline) were followed for incident hip fracture from the time they completed the baseline exam (1988 to1989) until December 31, 2005. HR and 95% CI were estimated for energy-adjusted dietary fatty acid exposure variables [(n-3) fatty acids: alpha-linolenic acid (ALA), EPA, DHA, EPA+DHA; (n-6) fatty acids: linoleic acid, arachidonic acid (AA); and the (n-6):(n-3) ratio] and fish intake categories, adjusting for potential confounders and covariates. Protective associations were observed between intakes of ALA (P-trend = 0.02) and hip fracture risk in a combined sample of women and men and between intakes of AA (P-trend = 0.05) and hip fracture risk in men only.  Participants in the highest quartile of ALA intake had a 54% lower risk of hip fracture than those in the lowest quartile (Q4 vs. Q1: HR = 0.46; 95% CI = 0.26?0.83). Men in the highest quartile of AA intake had an 80% lower risk of hip fracture than those in the lowest quartile (Q4 vs. Q1: HR = 0.20; 95% CI = 0.04?0.96). No significant associations were observed among intakes of EPA, DHA, EPA+DHA, or fish. These findings suggest dietary ALA may reduce hip fracture risk in women and men and dietary AA may reduce hip fracture risk in men. (Authors Abstract)

PUFA may affect bone health via multiple mechanisms by modulating inflammatory cytokine production and prostaglandin E2 production. n-3 fatty acids have been shown to favorably affect intestinal calcium transport and calcium excretion and are hypothesized to exert effects on bone by serving as ligands for PPARalpha and PPARgamma and by functioning as pro-resolving lipid mediators. In adult human studies, protective effects have been observed for n-3 fatty acid intake and a lower n-6:n-3 fatty acid ratio, in relation to hip bone mineral density (BMD), and for alpha-linolenic acid (ALA) in relation to bone resorption. The association among individual types of short- and long-chain n-3 and n-6 fatty acids and fish intakes with hip fracture risk was evaluated over 17-y of follow-up among older adult men and women in the Framingham Osteoporosis Study. In this longitudinal observational study, ALA intake was significantly associated with reduced risk of hip fracture in a combined sample of women and men, and AA intake was significantly associated with reduced risk of hip fracture in men but not women. Fish consumption, intakes of the n-3 fatty acids derived from marine sources (EPA, DHA, and EPA+DHA) and the (n-6):(n-3) fatty acid ratio were not associated with hip fracture risk. These findings suggest that the protective effect of ALA on hip fracture risk in humans may be independent of bone mineral density (BMD), because adjustment for baseline BMD did not substantially attenuate this association. ALA may reduce hip fracture via alternative mechanisms, such as protective effects on bone quality.  The strongest protective effects of ALA were observed among participants in the highest quartile of energy-adjusted ALA intake, which corresponded to a mean ALA intake of 1.39 g/d. This level of intake can be easily achieved in flaxseed and flaxseed oil. Further population-based research is needed to confirm the results. (Editor's comments)