A study involving healthy men and women fed a baseline diet containing 550 mg choline/day (the adequate intake level set by the Institute of Medicine) for 10 days, then put on a low choline diet (50 mg choline/day) for up to 42 days, has found that the "right" amount of choline depends on many factors, including gender, age, and ethnicity.
http://www.eurekalert.org/pub_releases/2014-03/foas-osd032714.php