Circadian rhythm of serum concentration of small dense low-density lipoprotein cholesterol

BACKGROUND: The atherogenicity of small dense low-density lipoprotein (sdLDL) has been reported and recently a new easy-handling method for measuring serum concentration of sdLDL cholesterol (sdLDLC) has been developed. Using this method, we observed the circadian rhythm of sdLDLC to determine the adequacy of fasting measurement of it and to seek the modulator of the atherogenic lipoprotein. METHODS: Study population was consisted of 20 healthy volunteers (10 women and 10 men, mean age 28 y). They had 3 meals per day and blood samples were taken before and 2 h after every meal and next morning. Serum concentrations of sdLDLC and other valuables including triglyceride (TG) and remnant-like particles cholesterol (RLPC) were determined. RESULTS: Serum concentration of sdLDLC had a unique circadian rhythm that was highest before breakfast (fasting status), decreased after each meal, hit the bottom after dinner and then increased during at night. Fasting sdLDLC was highly correlated with TG levels. The sum of the 6 TG values during a day (i.e., average TG level) had higher correlation coefficient with sdLDLC than fasting TG or fasting RLPC. CONCLUSIONS: From the observation of the unique circadian rhythm, measuring sdLDLC at fasting status is exactly reasonable because it never underestimate the risk of atherosclerotic diseases. Measuring sdLDLC can also be used as a marker for average TG levels regardless of the existence of postprandial hyperlipidemia.