Egg yolk is a rich source of different choline-containing chemical forms, such as phosphatidylcholine (PC), lysophosphatidylcholine (LPC), and α-glycerophosphocholine (α-GPC).
Writing in Lipids in Health and Disease, the trial was conducted by researchers from Kewpie, Tokyo University of Agriculture and Technology, Kyushu University and Prefectural University of Kumamoto, and Nihonbashi Cardiology Clinic.
A total of 60 healthy participants aged 60 to 80 without dementia but were informed to be forgetful took part in the randomised, double-blind, placebo-controlled, parallel-group study.
The intervention group took seven soft capsules amounting to 300mg of egg yolk choline provided by Kewpie Corporation while the control group took the placebo daily for 12 weeks.
The participants' blood plasma choline levels were measured during the 6th and 12th week of the trial, while changes in their cognitive performance were assessed using Cognitrax, which comprises seven tests across verbal and visual memory etc.
Findings showed a significantly higher verbal memory test score in the intervention group as compared to the placebo group at 6th and 12th week of the trial.
Verbal memory test assesses the participants’ memory by keeping track of the number of words that they could remember in a short period of time.
For the intervention group, their verbal memory score had increased 3.35 from baseline while that of the placebo was down 0.33 at week six. At week 12, the former’s verbal memory score was up 2.75 from baseline and the latter saw an improvement of 0.33.
“The results showed that there was a significant improvement in the choline group as compared with the placebo group in verbal memory ability, a part of the cognitive function,” said the researchers.
Slower processing speed
However, the intervention group showed a significantly slower processing speed and a lower symbol digit coding scores as compared to the placebo group at week six.
These tests were conducted to calculate the rate of processing efficiency and the test scores were significantly higher in the placebo group.
For example, the intervention group’s processing speed score was down 1.40 – significantly lower than the baseline, while that of the placebo group was up 2.86.
However, because the above effect disappeared by the end of the trial, the researchers believe that there could have been temporary factors which had led to the fluctuations.
Plasma free choline levels
Plasma free choline levels were significantly higher in the intervention group at the 6th week, with an increase of 1.80 μm from the baseline – higher than the placebo group’s slight increment of 0.34 μm.
Although plasma free choline levels in the intervention group was 1.06 μm higher at week 12 as compared to the baseline, this increase was not statistically significant.
“Low plasma free choline levels are associated with low cognitive function, suggesting that plasma free choline levels and cognitive function are closely related.
“In the present study, ingestion of egg yolk choline also increased plasma free choline levels, suggesting contribution to the improvement of verbal memory.”
In fact, chicken egg is listed as one of the foods recommended for increased consumption during old age in Japan, as it could reportedly help prevent dementia, said the researchers.
Mechanisms
Choline plays a role in cognitive function as it is the precursor of the neurotransmitter acetylcholine which is associated with memory and learning functions in the brain.
The researchers explained that choline transported to the brain is thought to cross the blood–brain barrier and reach brain cells via the choline transporter CHT1 or CHT2.
After reaching the neurons, choline and acetyl-CoA are converted into acetylcholine by choline acetyltransferase.
Acetylcholine released extracellularly at nerve terminals is implicated in memory and learning functions in the brain by stimulating muscarinic and nicotinic acetylcholine receptors, said the researchers.
“In the present study, egg yolk choline-containing PC, LPC, and α-GPC were ingested, and plasma free choline levels were confirmed to be elevated, suggesting that egg yolk choline served as an acetylcholine precursor in the brain, resulting in increased acetylcholine levels and the maintenance and improvement of verbal memory abilities involving acetylcholine receptors.
“No change was found in plasma fat-soluble choline levels, which were thought to be strongly influenced by blood phospholipid variations. However, the pharmacokinetics of plasma free and fat-soluble choline remained to be clarified,” they said.
Source: Lipids in Health and Disease
Effects of egg yolk choline intake on cognitive functions and plasma choline levels in healthy middle-aged and older Japanese: a randomized double-blinded placebo-controlled parallel-group study
DOI: 10.1186/s12944-023-01844-w.
Authors: Yamashita S, Kawada N, Wang W, Susaki K, Takeda Y, Kimura M, Iwama Y, Miura Y, Sugano M, Matsuoka R.
