Page 36 - Today's Dietitian (February 2020)

Choline

and
CVD

By Carrie Dennett, MPH, RDN, CD
C holine is an essential nutrient that plays a criti- the richest sources of choline. What about plant-based eaters?
Animal foods, especially eggs, beef, chicken, fish, and milk are
cal role in several biological processes, but one
Cruciferous vegetables, certain beans, nuts, seeds, and whole
byproduct of its metabolism is a molecule that’s
1,2
been receiving much negative attention—tri-
grains also contribute choline to the diet. In spite of that vari-
methylamine N-oxide (TMAO). Since TMAO was
5
concerning, because choline plays a role in the epigenetic reg-
first reported as having a link to CVD in 2011,
6,7
it’s been the focus of hundreds of research stud- ety, it’s estimated that only 11% of Americans reach the AI. That’s
ulation of gene expression, is a precursor for synthesis of the
ies. However, it remains unclear whether TMAO is a causal link neurotransmitter acetylcholine, and is a component of the major
between diet and CVD, or whether it’s simply a possible marker phospholipids in cell membranes. Since choline is essential for
1,3
of underlying disease. transporting lipids from the liver, choline deficiency can lead to
Because the precursors of TMAO synthesis, including choline, nonalcoholic fatty liver disease (NAFLD), which may be revers-
have many health benefits, suggestions that people should limit ible with choline repletion through supplementation. Although
3,7
dietary sources of choline, including eggs and meat, to prevent CVD most women of childbearing age are resistant to NAFLD because
may be premature. It seems that every day, dietitians learn more of their high estrogen levels, at least 40% have a polymorphism
about the complex interconnections between nutrition, genes, and that removes this protection, so adequate consumption of dietary
the gut microbiota in affecting health. This is one of those cases. choline is important. 8
So where does TMAO enter the picture? When humans ingest
Choline and Its Health Benefits foods containing choline or carnitine, an amino acid derivative, it
Despite the liver’s ability to synthesize choline, people need dietary provides certain gut microbes with the materials to produce tri-
choline as well, so the Institute of Medicine recognized choline as methylamine (TMA), which then enters the portal circulation and
9
an essential nutrient in 1998. There’s no Dietary Reference Intake travels to the liver, where enzymes oxidize TMA to TMAO. Most
1
for choline, but the daily Adequate Intake (AI) for adults is 425 mg TMAO is excreted in the urine within 24 hours, about one-half of
for women aged 19 and older, 450 mg during pregnancy, and 550 it unchanged, and about one-half being converted to TMA then
10
2
mg for men and lactating women. Recommendations are higher back to TMAO in the liver.
during pregnancy and lactation because choline is important for About one-third of choline in food is free choline, which gut
normal fetal and early childhood development, including reducing microbes prefer. Most dietary choline is in the form of the phos-
the risk of several birth defects linked to choline deficiency. Low pholipid phosphatidylcholine, which isn’t an efficient TMA pre-
10
maternal choline intake and plasma choline levels are associated cursor. Eggs are rich in choline, while beef is rich in both choline
with higher risk of neural tube defects, even when intake of dietary and carnitine. However, most of the choline in eggs isn’t free cho-
11
folate or supplemental folic acid is adequate. In addition, several line but is bound up as part of lecithin, and lecithin also is a weak
3,4
10
randomized controlled trials have shown a beneficial effect of precursor for TMA. Notably, fish and seafood contain preformed
1
maternal choline supplementation on the brain health of offspring. TMAO, which protects enzymes in the fish from salt water. 11
36 TODAY’S DIETITIAN • FEBRUARY 2020