Regulation of serum cholesterol level in middle-aged and elderly men. Relation of cholesterol absorption and synthesis to lipoprotein metabolism
Gylling, H.; Strandberg, T.; Tilvis, R.; Miettinen, T.A.
Arteriosclerosis and Thrombosis a Journal of Vascular Biology 14(5): 694-700
The aim of the present study was to investigate cholesterol absorption and cholesterol and bile acid synthesis and relate these values to kinetics of low-density lipoprotein (LDL) apoprotein (apo) B in 50 - and 75 -year-old men to find out why and by which mechanism serum cholesterol level decreases with advancing age under normal home-living conditions. The daily calorie, fat, and cholesterol intakes were lower in the 75-year-old men because the physiological requirements of daily energy are reduced in old age. However, absolute body weight was identical in the two groups, indicating isocaloric energy intake. Serum levels of total and LDL cholesterol were insignificantly lower but those of LDL apo B significantly lower, so that the LDL cholesterol/apo B ratio was higher in the elderly men. The mean reduction of LDL apo B by 26% (P lt .05) in the old men was associated with a 30% (P lt .05) decrease in transport rate (TR) and a 3% (P=NS) decrease in removal (FCR) for LDL apo B. However, at the comparable apo B levels, both TR and FCR for apo B were significantly lower in the old than in the younger men. Cholesterol absorption efficiency, bile acid synthesis, fecal neutral and total sterol excretion, and cholesterol turnover but not synthesis were reduced in the elderly men. Cholesterol absorption efficiency was positively correlated with LDL cholesterol and apo B, TR for LDL apo B, and dietary fat, cholesterol, and energy intakes and inversely with cholesterol synthesis, so that at the comparable absorption efficiency and low absolute absorption, cholesterol synthesis was surprisingly low in the older men, lower than in the younger men. Thus, low LDL level in the old men is contributed by reduced cholesterol absorption, which insufficiently stimulates cholesterol synthesis, and is related to low LDL apo B transport and to low but isocaloric food intake. LDL level is mainly influenced by reduced LDL apo B transport rate, the contribution of decreased removal rate being less consistent.