Choline
Before the recent DRI update, this nutrient was relegated to the lists of also-rans or, worse, vitamin impostors. But the Institute of Medicine recently raised this nutrient from obscurity to a more legitimate status. Soon after scientists discovered choline in 1862, they were able to synthesize the compound. And as researchers began to learn about choline's key functions, the only question that remained was, is choline an essential nutrient? At first glance, most scientists said an emphatic no, since the body can make choline out of several compounds. As that is the test for essentiality, the consensus ran in favor of the nays for several years.
Those researchers who believed choline to be essential cited these facts: human cells grown outside the body require choline to survive; people fed a choline-deficient diet have low blood levels of the nutrient; malnourished patients have low blood levels of choline; and in other primates, a choline-deficient diet causes liver failure. But other scientists countered that just because a person's blood level is low doesn't mean the nutrient is essential. A quick lqok at some of choline's roles would suggest an important compound that may deserve to be called essential. Some of these roles include helping to make phospholipids such as lecithin and the neurotransmitter acetylcholine.
What finally won over the committee with the power to confer the honor of essentiality or at least conditional essentiality? Probably studies showing that in periods of human growth and development, the need for choline outpaces the amount the body can make. This suggests that, at least during critical periods, a person needs to have a dietary source of choline. Other conditions that call for more choline than the body can produce include aging and certain neurologic disorders. Some research has suggested that choline may be a protective factor in several chronic diseases, but the work is mostly theory based on lab studies.
Foods containing choline include eggs, liver and other organ meats, milk, legumes, and nuts. People who take lecithin as a dietary supplement add to their choline intake. One problem can be our intestinal bacteria; they often add to our nutrient status as with vitamin K, but they tend to break down choline, making it unavailable for the body to absorb. The DRI committee set an Adequate Intake (AI) for this newcomer of 550 micrograms for men and 425 micrograms for women.
You might recall that an AI is different from an RDA in that for many nutrients (choline is one) the research data aren't quite as solid as for other nutrients. Both an AI and an RDA are estimates of how much of a particular nutrient you need, but when scientists have better evidence, they set an RDA. The DRI committee also set a tolerable upper limit (UL) for choline of 3.5 mg, stating that doses above this level could cause low blood pressure or a fishy body odor in some people.