Effects of acute mental stress on serum lipids: mediating effects of plasma volume.

The present study assessed the acute effects of mental stress (mental arithmetic) on serum cholesterol, triglycerides, high-density lipoprotein-cholesterol (HDL-C), and low-density lipoprotein-cholesterol (LDL-C), and the extent to which stress-induced changes are attributable to decreases in plasma volume. Total cholesterol, triglycerides, HDL-C, and LDL-C were assessed in 18 healthy men (35 +/- 7 years) during a resting baseline (30 minutes), challenging mental arithmetic (math; 10 minutes), and recovery (30 minutes). Five additional subjects served as controls receiving no stress intervention. An indirect estimation of the change in plasma volume was computed from hematocrit and hemoglobin at each time point. Results indicated significant (p < .001) increases in cholesterol, triglycerides, LDL-C, and HDL-C levels during mental arithmetic. Changes in lipid levels during stress were not related to plasma epinephrine levels or changes. Significant (p < .002) increases in hematocrit and hemoglobin levels reflected a 9.23% decrease in plasma volume during mental arithmetic. Correcting for this decreased plasma volume, changes in cholesterol, triglycerides, HDL-C, and LDL-C levels during math were no longer significant (p > .16, p > .23, p > .27, and p > .42, respectively). These results indicate that acute psychological stress can cause a rapid and substantial decrease in plasma volume, producing hemoconcentration. Thus, stress-mediated increases in circulating lipid concentrations are a secondary result of decreased plasma volume, perhaps due to vascular fluid shifts. Methodologically, stress-induced hemoconcentration during mental stress suggests that acute plasma volume decreases may need to be evaluated in studies of the biochemical effects of stress on high molecular weight substances.