NEW YORK (Reuters Health) - Some men and women who consume the recommended daily amount of choline, an essential dietary nutrient, may still develop an insufficiency and experience liver dysfunction as a result, new study findings suggest.

"Some humans may need more than the recommended amount of choline for optimal health," study co-author Dr. Kerry-Ann da Costa, of the University of North Carolina at Chapel Hill, told Reuters Health.

Choline, found in foods as varied as liver, beef, eggs, ice cream and chocolate, plays an important role in the formation of cell membranes -- the outer sheath that keeps cells intact. In addition, the nutrient is a building block for the neurotransmitter acetylcholine and other chemical messengers in the brain.

The United States Department of Agriculture (USDA) currently recommends that men and women consume 550 milligrams and 425 milligrams, respectively, of choline each day to prevent liver dysfunction. Yet, nearly one in five individuals in the current study needed much more choline -- 825 milligrams, in some cases -- to prevent or reverse the damage caused by a deficiency of this nutrient.

The current study, published in American Journal of Clinical Nutrition, was undertaken to refine the USDA's recommendation by determining the amount of choline needed to fulfill individual's dietary requirements, not just to prevent liver dysfunction.

The study included 57 healthy adults -- 26 men, 16 premenopausal women and 15 postmenopausal women - who consumed a daily diet consisting of 550 milligrams of choline for the first 10 days. The subjects were then put on a diet for up to 42 days that contained less than 50 milligrams of choline, and were also randomly assigned to received folic acid supplements or no folic acid supplements.

By the end of the study, 39 participants, including more than three quarters of the men and postmenopausal women, showed signs of liver dysfunction, the researchers report.

Pre-menopausal women appeared to be less affected by the choline deprivation, however, with only 44 percent exhibiting liver dysfunction.

Contrary to prior research, folic acid did not appear to influence the subjects' susceptibility to choline deficiency.

Noting the previously reported importance of choline in fetal development, co-author Dr. Steven H. Zeisel, also of UNC at Chapel Hill, explained that "evolution designed women" so choline levels wouldn't get too low. Pre-menopausal women's "ability to make it from scratch is turned on by estrogen," he continued. However, men and post-menopausal women don't have enough estrogen to do this.

SOURCE: American Journal of Clinical Nutrition, May 2007.

REUTERS