Reliability of fatty acid composition in human serum phospholipids

Objective: We examined the reliability of the fatty acid composition of ser um phospholipids in the New York University Women's Health Study, a prospec tive study of sex hormones, diet and breast cancer. Design: Non-fasting serum samples collected at three yearly visits, in 46 h ealthy women, and stored at -80 degrees C for 7-12 y, were included in the study. Serum phospholipid fatty acid composition was measured by capillary gas chromatography. Results: For the 20 individual fatty acids measured, the reliability coeffi cients were less than 0.50 for four, between 0.50 and 0.70 for nine, and gr eater than 0.70 for seven. Among the major fatty acids, arachidonic and alp ha-linolenic acids had high reliability coefficients (0.71 and 0.72, respec tively), palmitic, oleic, linoleic, eicosapentaenoic and docosahexaenoic ac ids had intermediate coefficients (0.57, 0.69, 0.62, 0.64 and 0.66, respect ively), whereas stearic acid had the lowest coefficient (0.15). The reliabi lity coefficients for total monounsaturated fats, omega-6 and omega-3 fatty acids were moderately high (0.66, 0.53 and 0.66, respectively), whereas th e coefficients for total saturated fats and total polyunsaturated fats were low (0.31 and 0.43, respectively). Conclusions: These results indicate that the fatty acid composition of seru m phospholipids can be a useful tool in epidemiologic studies, although for most fatty acids a single determination is associated with some error in m easurement that should be taken into account at the design and analysis sta ges. Storage for up to 12 y at -80 degrees C preserved polyunsaturated fatt y acids from oxidation very well.