It’s high time we covered acetylcholine — the most plentiful neurotransmitter in the body. And our Know Your Neurotransmitters series continues with the best guest possible to talk to us about acetylcholine: Dr. Steven Zeisel, MD, PhD.
Dr. Zeisel, UNC Nutrition Research Institute Director, was involved in the first study of the effects of choline — the nutrient precursor to acetylcholine — on humans.
What’s the Big Deal About Choline?
In Dr. Zeisel’s first experiment with humans, he fed men and women a diet deficient in choline. Most men and postmenopausal women became ill when deprived of choline.
Their bodies weren’t able to produce their own choline and they began to experience liver problems: fatty liver accumulation and liver cell death. These problems reversed within a few days of reintroducing choline to their diet.
For younger women, however, 55% did not experience any negative effects from choline deprivation. The difference? Estrogen.
There’s a gene in our livers, PEMT, that can produce choline but it’s only turned on by estrogen. Neither men nor postmenopausal women produce enough choline to switch on the gene. And those 45% of women who did get sick? They have a gene “misspelling” that makes their PEMT gene unresponsive to estrogen.
Why We Need Choline
For adults, choline deficiency can have two serious consequences. For most people, lack of choline means that your liver is unable to properly process fat, and you get fatty liver. A fatty liver puts you at risk of prediabetes and liver cancer. For 10% of adults, choline deficiency leads to muscle breakdown.
But for fetuses and infants, insufficient choline has even more devastating consequences.
Choline is absolutely essential in developing a normal brain. The development of the hippocampus, the memory center of the brain, requires choline. The development of the frontal cortex, responsible for high-level thinking, requires choline.
And lack of choline in the earliest stages of development impairs a child’s mental function for years to come. A high intake of choline during pregnancy results in higher cognitive performance in children at 7 years old.
Choline & Acetylcholine
Choline is a precursor to the neurotransmitter acetylcholine. Nerves use choline to make acetylcholine, which acts as a messenger between nerves — a huge variety of nerves.
Acetylcholine tells muscles to twitch and more, but it also tells your hippocampus to store a memory. It plays an essential role in alertness, attention, learning, and memory. It’s so essential to memory, in fact, that acetylcholine deficits are associated with Alzheimer’s disease.
Getting Enough Choline
Clearly, it’s important to get enough choline in your body. Foods that are high in fat and cholesterol are also generally high in choline. That means eggs and meat, particularly beef (418mg of choline per 100g) and chicken liver (290mg/100g), are the best dietary sources of choline.
Don’t despair vegans, as wheat germ (152mg/100g) is also a good source of choline. You can also take a choline supplement, like CDP Choline.
As for how much choline you should aim for a day, women need 400mg, 450mg if pregnant. Men should aim for 500mg of choline a day.
There can be too much of a good thing, however. Don’t get more than 3g of choline per day. That much choline will cause low blood pressure, and potentially increase your risk of heart disease.
PS: Want more awesome, brain-boosting content? We’ll send you the latest and greatest in neuro-news once a week!
Dr. Steven Zeisel: The area that I work in is a nutrient that when I started out my career, nobody believed was important. I was very lucky that this nutrient called choline, I thought was important and had no competition and therefore had a wide open field for proving what its role was in people.
Jesse: What gave you the inkling that there was something worth looking at there?
Dr. Zeisel: I knew that mice, and rats, and dogs became sick when they were deprived of choline and yet all the textbooks said that humans didn't become sick and could make it themselves and didn't need it. I just didn't believe that.
We conducted the first experiment in humans in which we took humans, put them into a research facility, controlled their diet completely, fed them a diet that contained enough choline, and then took it away. What we found is that most men and postmenopausal women became ill when deprived of choline with the majority of them presenting with liver problems, fatty liver accumulation, and death of liver cells. This reversed within days when we gave them choline back in their diet.
Young women were somewhat different, and we found that about 45% behaved like men and postmenopausal women and became sick in this way. 55% could care less about eating choline for as long as seven weeks in the hospital before we gave up and said we didn't think we could show that they needed choline.
Jesse: Interesting. What do you think was the difference in those populations?
Dr. Zeisel: Well, one of the things that was different is women have estrogen. So immediately we asked ourselves, is there something about estrogen that has to do with the required choline? We found that the gene in your liver named PEMT, that gene could make choline from scratch. It actually made another molecule called phosphatidylcholine from which you could release the choline in the liver but it was turned on by estrogen. It turned out that young women have high enough estrogen levels that they can turn on this gene and make some of their own choline and therefore needed less in their diet. While men don't have any estrogen and postmenopausal women have low enough levels of estrogen that they don't do this well.
Women start out with maybe 10 units of estrogen in their blood and may increase it two or three fold during pregnancy that the levels achieved in pregnancy are able to maximally turn on this gene. And so this looks like a design to try to make pregnant women less sensitive to the amount of choline in their diet. Now you might ask me why then did 45% of young women get sick.
Jesse: I was going to ask that.
Dr. Zeisel: What happened was when we looked at all of those young women, they had a gene variation. I guess I can call it a misspelling of the gene that made their gene unresponsive to estrogen. The switch didn't work. So even though they had estrogen they were reduced to the sad state of men, they couldn't turn on this gene. And so they had to eat it. And when we took it away from those young women, they behave just like men and postmenopausal women. So almost half of the population has a gene spelling difference that makes them not able to turn on their own supply of this nutrient during pregnancy.
Jesse: It stands to reason that we must have a pretty robust fallback mechanism in the diet or you wouldn't have this weakness in that high of a percent of the population. Traditionally, where does choline come into the human diet?
Dr. Zeisel: So the story is an interesting one. So our choline comes from foods that are usually high in fats and cholesterols. So eggs, meat are good sources while many plants are not great sources. We thought about that and said “Well, what if we go to West Africa.” I flew out to the Gambia and collaborated with a research center in the Gambia to collect DNA from young women of pregnancy age in the Gambia. In the Gambia they ate a diet that we calculated was less than half, maybe a third of what's eaten in the United States or Europe. There, to our surprise, all of the spelling differences that made a difference to whether people needed to eat choline and there's more than just the one I talked about, there's about five or six others we've identified, all of them are missing in the Gambia because they've eaten for thousands of years a diet missing choline. While in Europe and the United States, most people ate diets that contained eggs and meat and in fact when I grew up in the 1950s every mother wouldn't dream of not feeding their child eggs several times a week for breakfast because it was part of a normal diet.
I think in about 1975, nutritionist in cardiology has started to worry about cholesterol intake more and started to recommend people cut back on those foods and without realizing it, we’re telling people to cut back on foods containing choline and such that the U.S. NHANES study which is five year repeating a survey conducted by the Centers for Disease Control on people's diets in the United States reports that <7% of women of pregnancy age are achieving the adequate intake level of this nutrient. So 93% aren't getting the recommended intake. The recommended intake for a young woman is about 400 milligrams. A little bit more if their pregnant 450 milligrams. And for a man about 550 milligrams and most of that is based on body weight. So about half a gram a day is the recommended intake. A quarter of the U.S. population is taking less than half of that. So it's a problem nutrient and probably recently a problem nutrient because we changed our diets to try to be healthier.
Jesse: The words choline and cholesterol, they look suspiciously similar on the page both starting with -chol. Biochemically, are there commonalities we should be talking about?
Dr. Zeisel: Choline is a nutrient involved in what we would call one carbon metabolism and its most closely related to the folate, a vitamin or artificial vitamin that you take in a pill. Both of them have to do with transport of one carbons but choline’s main use is to make the wrappers around your cells called membranes. Several compounds are made out of choline that are reporting for that.
We also make a nerve messenger chemical called acetylcholine out of it and it's the main nerve messenger chemical that comes out of your brain and talks to the rest of your body. We finally use choline in this process called methyl donation which is needed to make a lot of other molecules and to metabolize a lot of molecules and also to put marks on our genes that switched them on and off. So choline and folate are highly related to one another. Their two parallel pathways interact a lot with one another but choline has its own special requirements and needs.
Jesse: So it sounds like there certainly are ways of getting choline within the diet. Is there such a thing as too much choline within the diet? Are there downsides if you go well beyond that half a gram or so per day that a person should have for basic physiology?
Dr. Zeisel: Yes. Recommendation is not to go above three grams a day because at that level you get some side effects. Low blood pressure, et cetera because nerves are making too much of the nerve transmitter chemical acetylcholine that our recent set of papers suggests that our gut microbes might metabolize choline to make a molecule called TMA and TMAO that may increase our risk for heart disease. So if we eat too much of this nutrient we might be making more of that molecule that's relatively new and not fully engraved in granite yet.
And so back to the story of choline and pregnancy, because of that we ask “Well, what is it doing?” And we found that (1) babies and fetuses have extremely high concentrations of choline. In the womb, a baby has about 15 times more choline in their blood than the mother has. The mother is transporting it across the placenta to the baby while dumping her choline into the baby to try to help it grow into a good baby. After birth, the mammary gland making milk is making a very rich source of choline in the milk and in fact until we discovered it people didn't realize that the choline in milk was often much higher than the choline present in artificial formulas.
In 2007, all of the commercial manufacturers of infant formula humanize the choline content of their formula. So whether they come from soybeans or cow milk, they made them match what's in human breast milk. Before 2007 however, infants fed on many of the soy based formula. We’re getting about half the choline that they would have gotten from milk.
So we then asked why is that important, and what we discovered was that the development of the brain depends on the availability of choline. We found that the number of nerve stem cells we call the nerve progenitor cells form depends on choline. When there's too little choline, fewer are formed. As there's more choline, more are formed. We showed that development thereafter of the memory center of brain called the hippocampus and the thinking center of brain called the cortex, both are very much influenced by choline and we have a paper that appeared last year showing that the layering of the frontal cortex, in other words the normal maturation development of that area of the brain where you form many layers that go out and talk to the rest of the brain that that layering didn't occur if choline was too low. Now those were studies in mouse models. The only people data that we have is a study not by our lab but by a group at Harvard School of Public Health where they looked at choline intake during pregnancy in women in Boston area and found that the higher the choline intake during pregnancy the better the infant’s cognitive performance tested on a special test at seven years of age, the child's performance at seven years of age could be predicted by mother’s intake during the first and second trimester of pregnancy of choline.
And so that's encouraging that there might be this kind of development difference due to choline. And so we've continued to work in that area and are trying to explain at the very molecular mechanism how is choline doing this and are describing the exact steps in which it’s involved.
But in the bottom line, it appears that choline is very important for developing a normal brain and that the supply of choline comes from the mother and that if she's lucky and has her genes spelled right she is relatively insulated from eating poorly, but if she's one of the women who have this gene misspelling, she has to be more careful and eat more if she's going to get enough choline to deliver to the baby.
Now in this story about Africa, we found that those eating a low diet had very little. Somebody asked us well how are you sure this isn't just something to do with people evolved after leaving Africa to develop this misspelling. But what we found that we looked in an area of Africa where people ate a traditionally high choline diet and that's the Messiah in Kenya, they eat milk and blood because cattle are very important to their society, and they have all of the same spelling differences that we find in European populations or in US populations.
So it depends where your heritage is. If you come from an African heritage that ate in the vegetarian areas of Africa, those inefficiencies disappear during evolution because you weren't eating enough choline and you couldn't have good babies. And so the only people left are the ones who didn't have those spelling errors. While in the Messiah or in Europe where every mother was feeding either milk or blood or eggs, and there was plenty of choline in the supply, there wasn't that evolutionary pressure. You still have those spelling inefficiencies and they remained unimportant for hundreds of years until somebody got the good idea to take choline out of the diet while trying to reduce cholesterol. Now, they may be coming important again, and we have to think about what we might see which would be changes in brain function.
Jesse: It sounds like just making sure that you have enough choline in your diet is probably the right idea for everybody, but is this something that if you get your 23andMe done and you're a woman you could tell whether you have this snip that's going to allow you to endogenously produce your own choline? Is that something that they test for?
Dr. Zeisel: Yes. They test first some other genes that are important, but the one that we described as being most important, they can’t test because it doesn't work on their gene test. It has to be done by a different method. So you wouldn't get in on a 23andme but you'd get other genes that might be helpful in guessing what that gene is because they tend to travel together.
The other thing I'd say about choline is that I told you most people presented with liver problems when they were fed a low choline diet. And what we found is that we can predict the people who are going to develop fatty liver as they get fatter. In other words become obese, based on a genetic signature because choline is very important in packaging fat and getting it out of the liver and mailing it out to other parts of the body. If you don't have enough choline, the liver gets backed up with fat and it builds up and you get fatty liver that physicians are concerned about because that fatty liver affects your responses to insulin, makes you pre-diabetic and also can increase your risk of developing liver cancer which turns out to be the most rapidly increasing cancer in the United States at this time, may be linked to this obesity epidemic.
Jesse: A lot of people still have the idea that you are what you eat but essentially I think what you just said there is that by eating a diet high in fat you actually make your body better at processing fats and thus not getting fat yourself with all of necessary caveats about healthy fats et cetera.
Dr. Zeisel: And the other thing we found when we had them in low choline diet is was about 10% of people developed muscle breakdown. They had high levels of muscle enzyme called CK in their blood and it grows very high. And again that stopped happening and their muscles stop breaking down as soon as we fed them choline back. It turned out that this 10% of people who didn't present with liver but rather presented with muscle all turned out to have gene spelling difference in the genes for transporting choline into the muscle and for storing it in the muscle. And so again, we could predict who those people were. And again it may be that people who later in life are having trouble maintaining their muscle may be some of these people 10% of the population in North Carolina that have this genetic signature that they break down their muscles every time they're eating a diet low in choline and we're studying that now because it would be obviously very interesting because it's a big problem as you get older trying to obtain adequate muscle mass.
So choline turns out to be very interesting in liver, in muscle and in the infant development, around brain development. And so it's a good thing that we recognize that it was required for humans. In about 1998, the U.S. said a recommended amount of it, they called it an adequate intake. In 2016, the Food and Drug Administration converted this adequate intake to a recommended daily intake level. Again, about a half a gram.
If you wanted to find out how much choline is in foods, the U.S. Department of Agriculture has done extensive analysis of foods and has a list. You Google USDA food choline you'll get their tables and any dietitian physician or somebody else can go through those to see what foods contain what amounts of choline. And so to give you an idea, two eggs a day, maybe three eggs a day if they're a little smaller give you choline intake but again it’s in meat, it's in wheat germ. So you can get your choline in many ways but if you're eating a diet low in eggs and meat and vegans would be an example, then probably you need to look carefully. And my guess is ancient vegan recipes made sure people got enough but we have a lot of people eating vegetarian and vegan right now who are really pasteutarians who just like eating pasta and they might be getting themselves into trouble.
If you have any concern, get that USDA food table, look up what you're eating and see are you getting about half a gram a day. And if you're not, it would be wise to find a way to get half a gram a day because that's the recommended intake.
Jesse: And there are supplements topping off a person's supply of choline. Is there any reason why a supplement might be worse than getting it through a natural food source? Obviously, a natural food source has lots of advantages and that there will probably be good things that are going along for the ride but are the choline supplements that are out there, would they also be effective for a vegan for example?
Dr. Zeisel: Yeah. I would expect them to be and again the trick is not to take too much but to take just the right amount which is the half a gram a day. If you were to take two grams a day of a choline supplement, you might present much more to your gut bacteria than normal because you have a certain capacity to take it up in your intestines and everything leftover gets dumped down where the bacteria lives to be metabolized. Yeah. So it probably makes sense to divide it across the day rather than take one big dose in the morning.
Jesse: Can we talk a little about cholines leading to acetylcholine and some of the things that acetylcholine does within the nervous system?
Dr. Zeisel: Sure. So choline is made into a nerve transmitter called acetylcholine that's made mainly in nerves themselves and is used as a messenger and is used by a messenger for instance to the nerves that go to your muscles and tell them to twitch or move. It's the nerves that go to your memory center and are involved in storing memory. And in fact in Alzheimer's disease, those are the nerves that go first, the acetylcholine nerves. Many of the drugs available to try to treat early Alzheimer's disease are trying to increase the amount of acetylcholine being released by those nerves. Acetylcholine is used to help you make your lungs, your diaphragm so you can breathe. It makes your saliva get secreted. So when you've taken anti acetylcholine drug you get a dry mouth. If you present much more choline to a nerve, it will make more acetylcholine. So that's why one of the side effects of treating with large doses of choline is that the nerves and the heart make extra acetylcholine and that signal gets sent out to slow heart rate and so you get slow heart rate because it's sending more message with every signal.
But probably the major thing that choline is used for is to make these membranes wrappers around your cells and probably 1% of your dry body weight is made up of these choline molecules, so you use a lot of them to wrap every one of your cells. Then another choline compound is called sphingomyelin and nerves use that as insulator material. They wrap their long processes called axons with sphingomyelin so that they can send an electrical signal to fire without it shorting out along the way. So you need choline to make sphingomyelin as well. So if you didn't have enough, again you might make less of that. But the chief presenting problem in adults is either liver or muscle problems. That's what goes first and everything else may go later. But you notice it is having liver or muscle problems first. That's why our study stopped when we noticed that. That was enough to prove you needed it.
Jesse: You mentioned that the creation of acetylcholine from choline takes place primarily within the actual nerve cells. One thing that's gotten a lot of attention in recent years is the fact that a significant amount of neurotransmitters are actually created within the gut in the microbiome, is that less the case with acetylcholine with some other neurotransmitters or is there more to that story.
Dr. Zeisel: Yeah. So most of the neurotransmitters are specifically made in the nerves that want to use them as a signal. However there are many gut bacteria who make molecules that are turned out to be neurotransmitters but they weren’t using it for that. So a tryptophan is a good example. And your gut sees a lot of these transmitters and is affected by them but very few manage to get by the gut and certainly none get to your brain because of the blood brain barrier.
So yes, these bacteria may be making chemicals that are in the same molecules as your nerves are making but they weren't meant to be used in that way but there are side effects like whether you feel jittery or not may well be because they make more of that transmitter and you're absorbing it. And so your peripheral body outside of your brain has to manage it. Usually your liver gets rid of most of that so that it don’t sneak by. But bacteria make many of the molecules that human cells make but they make them for some other purpose. Humans probably during evolution just stole the idea.
But other things like dopamine get made by these gut bacteria and they do affect you more. Acetylcholine is rapidly chewed up as soon as it gets outside of the nerve cell, it's chewed up. The purpose of that is to not have it send false signals or prolonged signals. It lets you shut off the signal after it's released a little while after it's destroyed and you have to make it again. But the nerves are smart, it takes up the pieces and reassembles them.
Jesse: Nutrigenomix is something that we've never talked about on this show before and it's a term that I think probably a lot of people won't be familiar with but maybe if you can tell us what Nutrigenomix is and how this plays into the choline story.
Dr. Zeisel: Sure I'd be glad to. So Nutrigenomix is the study of how nutrients interact with genes and how genes interact with nutrients. The acetylcholine story is a good example of it. I've told you that there are people with slight variations in the spelling of certain genes and we call those single nucleotide polymorphisms or snips for short, SNP. They are quite common and we can predict people who have inefficient pathways in the metabolism of choline from whether they have these snips or not and then we can predict whether they're going to have health problems related to it and we could even try to figure out how can we bypass those health problems related to these genetic differences. So these gene spelling differences are the easiest part of Nutrigenomix that you can go out and get your genes tested.
What 23andMe and these other companies are often testing are just the spelling differences. They use a big chip and they can tell you whether you have any of 1.5 million of these polymorphisms, snips, spelling differences. And then for some of them they can tell you what they mean. The study of Nutrigenomics is trying to increase that catalog in the area of which genes make a difference to nutrition. But it won't only end in the spelling differences, Nutrigenomix because we know that harder to measure but just as important are marks that we put in our DNA that retune our genes early in life. And this area is called epigenetics and it turns out we put marks on our genes, chemical marks that switched the genes on and off and allow us to retune a little bit to face whatever environment we're seeing in our early life. So our genetic code isn’t our fate. We essentially have a capacity to make some readjustments.
And so we know that in early life for instance the availability of this nutrient choline I've been talking to you is extremely important in making some of these marks. There's a very interesting experiment with a set of mice that have normally a kinky tail and there's a gene making their tails kinky. And if they mark those genes with pieces from the choline molecule because the mother is eating a diet high in choline in other method of groups they shut those genes off and the babies for the rest of life have straight tails.
Then there's another mouse model where the mouse is either fat and yellow or skinny and brown. They're sisters from the same litter but whether they're fat or yellow or skinny and brown depends on whether they put certain marks on genes to turn them off so that they have a different presentation even though they have the same genes. So these early marks have formed a whole theory in pediatrics called that Dohad Hypothesis that early life exposures retune your genes in certain areas and later in life you are therefore differentially able to deal with your environment. So if maybe you were tuned early in life because you were short on nutrition, calories you became more efficient to burn your calories more efficiently and reset your whole metabolism. Genes that control it later in life when you get a lot of extra nutrients, you're going to still stay more efficient because these changes stick with you and you'll be more likely to have problems with obesity. So that's one of those theories that people believe they have evidence for. Same is true for heart disease blood pressure et cetera. It seems that in early life these metabolic retuning of our genes are very important and set us up for the rest of our life to be better or worse at handling certain environmental stresses.
Jesse: It's interesting because it sounds like in epigenetics there are some things that are set at one particular point in an animal's life cycle and then stay that way. They set it and forget it. Whereas other epigenetic settings can be continually monkeyed throughout the lifecycle depending on your environmental factors as you go through your life. Do we have a good sense of what differentiates those two or maybe more types of ways that epigenetic triggers work?
Dr. Zeisel: Yes. So again, most epigenetic settings are set in very early stages of development, in the embryo, and maybe a little bit after. We know that because the only reason our liver is different from our brain, they both have the same genetic code but different genes are turned on and off by epigenetic marks that makes them different. And that last your whole life. We sort of have epigenetics lost when tumors develop and that's why sometimes tumors, they lose these epigenetic marks, they begin to behave very poorly and they can form other tissues within the tissue because they've lost this other link. But cancer is the first time really you see epigenetic marks get changed commonly. There are a few tissues which seem to be resettable in their epigenetic marks but they are the exception not the common and they may be sensors designed to detect our environment in some way. So that's why they're designed to be allowed to reset. But for most tissues the only time they ever reset is for the worse when a cancer develops and they lose some of this specialization that made them settle or made them press outlets et cetera.
Right now, the biggest controversy in epigenetics is are they inheritable. There's some evidence that suggests they could be inheritable across generations but the absolute proof isn't there yet. But we know for instance that a grandfather's experience during the Dutch famine you can see in the grandchild who was never exposed to some effects and the only way we could see that being passed down is through some epigenetic mark that has been left in place and wasn't erased in the next generation.
But again that's something we have a lot do before we can say for sure that what grandfather eats could affect what granddaughter does.