Homocysteine: The Important Marker Your Doctor Might Not Be Ordering and Why You Should Care
There are certain labs that almost everyone recognizes, such as cholesterol, blood sugar, vitamin D, and iron.
Homocysteine isn't usually one of them.
Many of the patients I see have never had their homocysteine measured before coming to my practice. It isn't routinely included in a standard annual physical or conventional cardiovascular screening panel. But I’m not sure why. I think this misses useful information.
Homocysteine is a blood test that gives us insight into a few important aspects of health, particularly if we want to think about improving healthspan, which really, everyone does. It provides context about nutrient status, methylation, cardiovascular and cognitive health. It's a marker I like to check at least once a year as part of a comprehensive health assessment.
But as with most biomarkers, the goal isn't simply to get the number as low as possible. The more interesting question is what that number may be telling us about your underlying physiology.
What exactly is homocysteine?
Homocysteine is an amino acid produced as part of the normal metabolism of methionine, an essential amino acid that we obtain from protein.
You may hear about homocysteine in the context of methylation or MTHFR genetic variants, which we’ll come back to later.
If you’ve never heard of methylation, I’d like to give you two options:
Ignore this section and skip to the next section on why you should care.
Dive into science with this brief summary of an important biochemical process that is happening in your cells even as you read this:
Methyl groups are small chemical groups made up of one carbon and three hydrogens (remember high school chemistry? I’m guessing at some point you wrote down the formula for a methyl group, -CH3).
Your body uses methyl groups constantly for essential processes including turning certain genes on and off, metabolizing hormones and neurotransmitters, clearing excess hormones and toxins through detoxification pathways, among other similarly essential functions.
There are several interconnected pathways that help maintain the supply of methyl groups (for said important functions).
SAM (S-adenosylmethionine) is the body’s primary methyl donor, and homocysteine’s central role in this methylation cycle is what brings us here today.
Homocysteine sits at something of a metabolic crossroads.
We start with methionine, which we typically get in abundance from animal proteins.
Methionine is first converted into SAM. Once SAM donates its methyl group, it eventually becomes homocysteine.
From there, homocysteine can take one of two major paths.
It can be recycled back into methionine by the addition of a methyl group. This methyl group can come either through a series of reactions involving folate and vitamin B12, or from betaine, also known as trimethylglycine or TMG.
Or homocysteine can move through the transsulfuration pathway, where it ultimately contributes to the production of cysteine and glutathione, one of our major endogenous antioxidants. Vitamin B6 plays an important role in this pathway.
So, when we measure your homocysteine, we’re learning about how your methylation and transsulfuration pathways are functioning, including whether nutrients such as folate, B12 and B6 may be adequately supporting them.
In other words, homocysteine is an intermediate that gives us a window into how effectively several interconnected biochemical pathways are functioning.
Why should you care about homocysteine?
Because improving your healthspan means being proactive about lowering your risk of chronic diseases, including both cardiovascular disease and cognitive decline. And because higher homocysteine levels have consistently been associated with an increased risk of both, knowing your homocysteine level can help you make choices around how to best support your health.
Importantly, even though homocysteine correlates with an increased risk of cognitive decline and cardiovascular disease, there is no clear evidence to establish causation. Which means that we can't assume homocysteine itself is directly causing these conditions.
Clinical trials have shown that we can often lower homocysteine very effectively with B vitamins, but lowering homocysteine alone has not consistently translated into fewer heart attacks.
There is somewhat more intriguing evidence around stroke and cognitive health, including research suggesting that lowering elevated homocysteine may reduce stroke risk in some populations and may slow brain atrophy in certain people with mild cognitive impairment.
So from this, we can think of an elevated homocysteine level as an early indicator that we need to look further into why homocysteine might be high.
Is there a nutrient insufficiency? Are we seeing changes in kidney or thyroid function? Is there increased demand on certain metabolic pathways? And is this one potentially modifiable piece of a larger cardiovascular or cognitive risk picture?
An elevated homocysteine prompts us to consider those questions in the context of your health, allowing us to be more proactive.
What's an optimal homocysteine level?
This is another place where “normal” and “optimal” aren't necessarily the same thing.
Depending on the lab, the upper limit of the reference range may be as high as 10–15 µmol/L.
So while your homocysteine may be considered normal at 12, if we’re thinking about prevention and healthspan, a level around 7 to <9 µmol/L may be more reassuring.
This is not a universally established medical guideline, and we don't have clinical trials proving that moving a homocysteine level from, for example, 12 to 8 prevents dementia or cardiovascular disease.
But epidemiologic studies suggest that cardiovascular risk begins to rise as homocysteine moves above approximately 10 µmol/L, which is why identifying upward trends earlier can be useful rather than waiting for the number to rise clearly out of range.
Why might homocysteine be elevated?
The first question shouldn't be “Which supplement lowers homocysteine?”
It should be “Why is it elevated?”
Some of the more common possibilities include:
Inadequate folate, B12, or B6
Reduced kidney function, since the kidneys play an important role in homocysteine metabolism and clearance
Untreated hypothyroidism
Certain medications
Alcohol intake
Other factors that increase nutrient requirements or metabolic demand
This is why homocysteine is best interpreted in the context of other laboratory findings rather than in isolation.
What about alcohol?
Alcohol deserves a little nuance here.
You'll sometimes see alcohol listed simply as a cause of elevated homocysteine, but the research isn't quite that straightforward. The relationship varies with the amount and type of alcohol consumed, nutrient status, and probably individual genetics.
There isn't a single amount of alcohol at which everyone's homocysteine suddenly rises.
In women, however, some research has found higher homocysteine beginning around one standard drink per day, particularly when folate intake is low. At higher levels of alcohol intake, the association becomes more consistent.
It's also helpful to put the term “heavy drinking” into perspective. The National Institute on Alcohol Abuse and Alcoholism currently defines heavy drinking for women as four or more drinks on any day or eight or more drinks per week. That means just one to two drinks most nights could meet criteria for heavy drinking.
This definitely doesn't mean that a glass of wine is going to send your homocysteine soaring. It simply means alcohol is one of the variables worth considering when we're trying to understand an unexpectedly elevated level.
How can we lower homocysteine?
Once we've looked for underlying contributors, there are several nutritional and lifestyle strategies that can help.
Folate and vitamin B12
These are generally the first nutrients people associate with homocysteine, and for good reason.
Folate and B12 are necessary for remethylating homocysteine back into methionine. If either is inadequate, homocysteine can rise.
But before simply adding large doses of methylated B vitamins, it's more useful to look at the broader picture. Is B12 actually low? Is absorption impaired? What does folate look like? Are there medications affecting these nutrients?
More isn't always better.
Vitamin B6
Vitamin B6 supports the alternate route for homocysteine metabolism: the transsulfuration pathway.
So it can be important when homocysteine is elevated, although chronically taking unnecessarily high doses of B6 should be avoided because excessive supplemental B6 can cause peripheral neuropathy, or irritation to the nerves in your hands and feet.
Some of you may have noticed that I’ve been testing vitamin B6 levels more recently, and as a result, often scaling back on regular dosing recommendations.
TMG, or betaine
Trimethylglycine (TMG) provides another route for converting homocysteine back into methionine through an enzyme called betaine-homocysteine methyltransferase.
This can make TMG particularly useful when homocysteine remains elevated despite adequate folate and B12 status.
Exercise
Regular exercise may also help support healthier homocysteine levels over time.
The evidence isn't strong enough to think of exercise as a primary treatment for elevated homocysteine, but some studies suggest that regular physical activity, particularly resistance training, may help lower levels modestly.
Of course, exercise also improves cardiovascular and cognitive health through many pathways completely independent of homocysteine, which makes it an important part of the bigger healthspan picture regardless.
Creatine
This is where the biochemistry gets particularly interesting.
Your body can make its own creatine, but doing so requires a considerable amount of methylation capacity. In fact, endogenous creatine synthesis represents one of the body's major uses of methyl groups.
When we take creatine as a supplement, we reduce the amount the body needs to make itself. In theory, that decreases methylation demand and may consequently reduce homocysteine production.
There is some human evidence supporting this effect, but creatine still isn't nearly as well established as B vitamins or TMG specifically for treating elevated homocysteine.
Of course, creatine has plenty of other reasons to earn its place in the conversation, particularly for supporting muscle and increasingly for its potential benefits for brain health.
Choline and phosphatidylcholine
Choline provides another interesting connection.
Some choline can be converted into betaine, which can then help recycle homocysteine back into methionine. Small human trials suggest that higher choline intake, including phosphatidylcholine supplementation (which some of you will recognize as your BodyBio PC Complex supplement), can lower homocysteine.
Again, phosphatidylcholine is not typically used solely to lower homocysteine. But it illustrates an important concept: these metabolic pathways don't operate in isolation.
What if homocysteine stays elevated?
Sometimes the obvious pieces look good.
B12 is adequate. Folate is adequate. Kidney and thyroid function look appropriate. Nutrition is good. And yet homocysteine remains higher than expected.
At that point, it can make sense to broaden the investigation.
Depending on a person's health history and potential exposures, that can sometimes include looking at environmental toxin burden. Certain environmental exposures may increase oxidative stress and alter nutrient or glutathione demands, all of which intersect with the pathways involved in homocysteine metabolism.
An elevated homocysteine level alone is not evidence that you have a “detox problem,” and it isn't a reason to automatically order extensive toxin testing.
But an unexplained abnormality can sometimes be a reason to ask more questions.
Nerd Note: What about MTHFR testing?
People often ask about testing the MTHFR gene or other genes involved in methylation.
And a quick terminology note: common MTHFR variants are SNPs, or single nucleotide polymorphisms. I sometimes hear these referred to as “MTHFR mutations,” but that terminology is like fingernails on a chalkboard for me, so we’ll avoid it here.While genetics can sometimes provide useful context, routine testing of common methylation related genetic variants often adds less than people expect.
A gene variant tells us about a potential predisposition. But it rarely tells us what your biochemistry is actually doing.
Whenever possible, it's more useful to look downstream and measure the pathway in action.
Homocysteine is a perfect example.
Two people can have the same MTHFR variant and very different homocysteine levels depending on factors such as folate and B12 status, diet, alcohol intake, and other metabolic demands.
And someone without a significant MTHFR variant can still have elevated homocysteine.
In other words, the more useful question is often not whether your genetics suggest that a pathway might function differently, but whether there is evidence that it actually is.
The bigger picture
One of the most useful things about comprehensive laboratory testing is that an individual biomarker rarely tells the entire story.
Homocysteine is no exception.
A higher level doesn't automatically mean you need methylfolate, TMG, or any other specific supplement. The goal is to understand why the number is elevated in the first place.
What homocysteine can do is give us another piece of information.
It can point us toward nutritional or metabolic issues we might otherwise miss. And it provides useful context when we're thinking proactively about cardiovascular and cognitive health.
That's why, even though homocysteine remains largely absent from routine conventional screening, it's a marker worth knowing, and one that can be useful to follow over time rather than waiting until something is wrong.