Cholesterol in serum lipoprotein fractions after spaceflight.

Cholesterol, triglycerides, very low density lipoprotein cholesterol (VLDL-C), low density lipoprotein cholesterol (LDL-C), and high density lipoprotein cholesterol (HDL-C) were measured in blood samples from 125 crewmembers on the first 24 space shuttle flights. Samples were obtained before, immediately after, and 3-23 days after spaceflight. On landing day, only HDL-C was significantly changed from its preflight level; it had decreased 12.8%. Later in the postflight period, total cholesterol and LDL-C as well as HDL-C decreased significantly. Possible causes of these decreases in estimated cholesterol content of lipoprotein fractions include increased levels of thyroxine during flight and reduced physical activity. The postflight decrease in HDL-C is not considered to have clinical significance for shuttle astronauts, but lipoproteins and apolipoproteins should be measured in blood drawn during longer missions.