Reported effects of long-term freezer storage on concentrations of retinol, beta-carotene, and alpha-tocopherol in serum or plasma summarized.

A literature review of the effects of long-term freezer storage on concentrations of antioxidant micronutrients in serum or plasma showed that a high proportion of the studies that compared the concentrations of retinol, beta-carotene, or alpha-tocopherol in fresh and stored serum were deficient because of small numbers of observations, imprecise descriptions of procedures, and short periods of storage. Data from nested case-control studies of the associations of these micronutrients with cancer are confounded by differences in the study populations. Nevertheless, the overall impression is strong that retinol is stable at storage temperatures as warm as -20 degrees C for at least 15 years, that moderate losses of alpha-tocopherol occur at temperatures above -40 degrees C during that period, and that only a small proportion of beta-carotene persists at storage temperatures above -40 degrees C. At -70 degrees C or colder, all three micronutrients appear to be stable for at least 15 years.