Thursday July 10, 2014 (foodconsumer.org) -- Premarin, an exogenous estrogen by Ayerst Laboraories in New York can increase the risk of cholesterol gallstones while high cholesterol diet may overcome the side effect, a new study suggests.

In the study, 29 anovulatory women taking Premarin were tested to determine "gallbladder motor function, biliary lipid composition and secretion, cholesterol absorption, cholesterol synthesis and esterification by peripheral blood mononuclear cells, the clearance of chylomicron remnants, and bile acid kinetics."  Of the participants,13 women were on both a low cholesterol diet and a high cholesterol diet.

Premarin was found to increase the lithogenic index of bile, increase biliary cholesterol, lower chenodeoxycholate pool and synthesis, increase altered biliary bile acid composition and cholesterol esterification.

On the other hand, increased dietary cholesterol stimulated the secretion of biliary cholesterol, bile acid and phospholipid.  The reduction in CDCA pool and synthesis by Premarin was overcome by increased intake of dietary cholesterol.

The study concluded "We conclude that Premarin increases biliary cholesterol by enhancing hepatic lipoprotein uptake and inhibiting bile acid synthesis. These actions of Premarin divert dietary cholesterol into bile."  (David Liu, PHD)

G T Everson, C McKinley, and F Kern, Jr.  Mechanisms of gallstone formation in women. Effects of exogenous estrogen (Premarin) and dietary cholesterol on hepatic lipid metabolism.  J Clin Invest. Jan 1991; 87(1): 237–246