Vitamins raise levels of bad cholesterol

ANI[ TUESDAY, MAY 04, 2004 08:26:43 PM ]

WASHINGTON : A new study conducted at the New York University School of Medicine suggests that vitamins, such as E, C, and beta carotene could raise the production of the bad form of cholesterol in the liver, which transports cholesterol into the artery walls.

According to Edward A. Fisher, who leads the study, "It does appear that antioxidant vitamins may be potentially harmful for the heart based on their ability to increase the secretion of VLDL in the liver cells and in the mice that we studied."

After its secretion from the liver, VLDL is converted in the bloodstream to low-density lipoprotein (LDL), the so-called bad form of cholesterol. The liver is the major source of atherosclerosis-causing lipoproteins.

Overall, antioxidants usually have been considered healthful. The vitamins scavenge "free radicals," which are highly reactive and damaging forms of oxygen produced by natural metabolic processes in the body and by external sources like the sun's UV rays, ozone, and toxins in pesticides, among other things.

The new study by Dr. Fisher and his colleagues however indicates that antioxidants hamper a process in the liver that prevents the production of harmful lipoproteins. When cells are under "oxidative stress," free radicals produced by the normal conversion of polyunsaturated fatty acids to lipid peroxides bombard the cells.

The scientists discovered that liver cells respond by activating a pathway that breaks down ApoB100, a critical protein component of VLDL and other harmful lipoproteins. Deprived of ApoB, the liver cannot now produce these bad lipoproteins and their secretion into the bloodstream is reduced substantially.

The scientists also found that the polyunsaturated fatty acids increased the generation of lipid peroxidation products and stimulated the PERPP pathway. In addition to the studies with liver cells in laboratory dishes, they also demonstrated the relationship between lipid peroxidation and reduced production of bad lipoproteins in living mice.

Dr. Fisher plans to conduct further experiments in mice to confirm these findings. "Direct experimentation in people to explore the inner workings of the liver is difficult but there are already observational studies in normal people showing that a diet enriched in polyunsaturated fats increases blood levels of lipid peroxides and decreases levels of VLDL and LDL," said Dr. Fisher