November 4, 2010 — Saturated fatty acid intake may significantly increase hip fracture risk, whereas monounsaturated and polyunsaturated fatty acid intakes may decrease total fracture risk, according to results from the Women's Health Initiative reported in the October 27 online issue of the American Journal of Clinical Nutrition.
"Fatty acids (FAs) may be important dietary components that modulate osteoporotic fracture risk," write Tonya S. Orchard, from the Department of Human Nutrition, College of Education and Human Ecology, The Ohio State University in Columbus, and colleagues. "The primary hypothesis was that n-3 FAs would reduce the risk of osteoporotic fractures. Secondary hypotheses were that higher n-3 FA consumption from both marine and nonmarine sources would be associated with lower fracture risk, and higher intake of n-6 FAs as well as a higher n-6:n-3 FA ratio would be associated with increased fracture risk."
To evaluate the association of fatty acid intake with osteoporotic fractures, the investigators studied 137,486 postmenopausal women enrolled in the Women's Health Initiative. Food frequency questionnaires at baseline allowed estimation of fatty acid intake, which was standardized to total caloric intake. No data were available on omega-3 (n-3) fatty acid supplements. Total fractures were identified by self-report, and medical record review confirmed hip fractures. Fracture risk was estimated from Cox proportional hazard models.
Higher intake of saturated fatty acid was associated with a greater risk for hip fracture (quartile 4 multivariate-adjusted hazard ratio [HR], 1.31; 95% confidence interval [CI], 1.11 - 1.55; P for trend = .001). In contrast, total fracture risk was lower with a higher consumption of monounsaturated fatty acids (quartile 3 HR, 0.94; 95% CI, 0.89 - 0.98; P for trend = .050) and polyunsaturated fatty acids (quartile 4 HR, 0.95; 95% CI, 0.90 - 0.99; P for trend = .019).
Contrary to the study hypothesis, higher intake of marine n-3 fatty acids was associated with a greater risk for total fracture (quartile 4 HR, 1.07; 95% CI, 1.02 - 1.12; P for trend = .010), whereas higher consumption of n-6 fatty acids was associated with a lower risk for total fractures (quartile 4 HR, 0.94; 95% CI, 0.89 - 0.98; P for trend = .009).
"These results suggest that saturated FA intake may significantly increase hip fracture risk, whereas monounsaturated and polyunsaturated FA intakes may decrease total fracture risk," the study authors write. "In postmenopausal women with a low intake of marine n-3 FAs, a higher intake of n-6 FAs may modestly decrease total fracture risk."
Limitations of this study include lack of data on fish oil or n-3 fatty acid supplements; reliance on nutrient intake data from the food frequency questionnaire; use of a single questionnaire administered at baseline; observational design; and unavailability of inflammatory markers or serum vitamin D concentrations, precluding determination of causal or mechanistic associations.
"These results support current recommendations of 5–10% of total energy as n-6 FAs," the study authors conclude. "Although a beneficial dose of long-chain FAs cannot be determined from this analysis, our results suggest that the type of FA consumed may play a role in a diet that decreases osteoporotic fracture risk."
The National Center for Research Resources, the National Heart, Lung, and Blood Institute, National Institutes of Health, and the US Department of Health and Human Services supported this study. The study authors have disclosed no relevant financial relationships.
Am J Clin Nutr. Published online October 27, 2010.
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