Homocysteine: An Overlooked Factor in Dementia Prevention
Concerned about cognitive loss or dementia?
Posted September 2, 2025 | Reviewed by Abigail Fagan
“Homocysteine? What’s that?” you ask. I know. You and almost every one of my patients gets that same bewildered look when I mention homocysteine. It’s a technical word that you will not hear on a TV commercial for a “memory support” product that relies on a jellyfish protein or that shows a cartoon elephant touting his superb memory. And you won’t hear this in a commercial where actors struggle to find the name of a friend they encounter in a grocery store aisle. And yet, the research shows that homocysteine is very important in improving memory for many older people.
Let’s start with some dementia prevention facts.
It is now well-established that dementia of all types, including Alzheimer’s disease, is preventable in half of all people who are at risk[1][2][3]. Many of the modifiable factors, i.e., things that each of us can do to protect our brains, are well known. Exercise, social engagement, quality sleep, mental stimulation, blood pressure and blood sugar control, and correcting hearing loss are just a few. But homocysteine does not usually come up on your radar screen. It is a bit esoteric and complex, so I have enlisted the help of my partner in life and all things, Dr. Emily Clionsky, M.D., to help explain this. Not only has she practiced internal medicine ( attention to homocysteine really started in cardiac care), but she is also a dementia expert who is board-certified in psychiatry and neurology.
Imagine homocysteine as a byproduct of your body breaking down proteins. It’s normal to have some homocysteine, but when levels get too high—a condition known as hyperhomocysteinemia (HHcy)—it can disrupt your brain's chemistry and even affect its structure. Typically, a homocysteine level of 15 micromoles per liter (μmol/L) or higher is considered elevated, but some research suggests cognitive issues can arise at levels as low as 10 μmol/L.
This is a widespread problem. An estimated two out of three older adults have HHcy. Most importantly, it is often undiagnosed. A routine blood test can check for this, but doctors often only test for B vitamins like B9 (folate) and B12. If those levels are normal, testing often stops. The crucial step of checking homocysteine, which indicates how well those B vitamins are being used, is frequently missed.
The B Vitamin Connection
So, what's the link? Your body needs B vitamins—specifically, B9 (folate) and B12—to properly process and convert homocysteine into other useful molecules. When you don't have enough of these "active" forms of B vitamins, homocysteine levels rise.
This can be caused by an inherited genetic mutation (MTHFR C677T) that affects an average of one in four people and varies across racial and ethnic lines.[4] But even without this gene , you are more susceptible if you are older, eat a vegetarian or vegan diet , have kidney disease, have diabetes, smoke cigarettes, drink alcohol , and take certain medications.
High homocysteine levels have a documented impact on cognitive function, i.e., how you think. Studies have shown that people with HHcy tend to score lower on memory and problem-solving tests and will often show greater brain atrophy, or shrinkage, in key memory centers like the hippocampus. This is a concerning finding, for sure, but it also points to a powerful opportunity for intervention.
A Targeted Approach to Brain Wellness
The good news is that reducing elevated homocysteine levels has been shown to improve short-term memory and executive functions like planning and problem-solving. But simply taking a standard B vitamin supplement may not be enough. The problem isn't always a lack of vitamins; it's the body's ability to use them effectively. It’s like having enough gas in your tank, but the gas is not getting to the engine. You can add more gas, but that will only overflow the tank.
This is where a targeted nutritional approach comes in. Let’s be clear: I am not suggesting you eat more red meat or make a major life change. But you might take a supplement that includes the necessary vitamins in a form that your brain cells can use immediately and can lower your homocysteine levels. You should look for a product that contains L-methylfolate, a specific form of folic acid that's immediately available to the brain to support neurotransmitter production and help your brain create energy molecules. It should also contain methylcobalamin (Vitamin B12), which helps maintain nerve health. And to get the biggest bang for your vitamin buck, make sure it includes N-acetyl-l-cysteine (NAC), an antioxidant that protects brain cells from oxidative stress .
It turns out that this particular combination of ingredients has been shown, through actual scientific research on human subjects, to efficiently decrease their homocysteine levels and to slow the rate of cognitive decline and brain atrophy[5]. And that’s why this approach is different from relying on a product primarily backed up by customer testimonials or the opinion of a small-town pharmacist whose customers thank him for his recommendation. And it is why real science makes a difference.
Let’s remember that half of all dementia cases may be prevented by addressing modifiable health and lifestyle factors. But the approach for each person varies and can be complex. You want to figure out where you can make a difference in your health and lifestyle that is tailored to you. But, for many people, awareness of homocysteine is a great place to start. If you're concerned about your memory, have a conversation with your health care provider about checking both your homocysteine and methylmalonic acid levels and consider the potential benefits of a targeted nutritional strategy.
[1] Livingston G, et al, Dementia Prevention, intervention and care, Lancet 2024 DOI: https://doi.org/10.1016/S0140-6736(24)01296-0
[2] Ehrlich JR, et al, Addition of vision impairment to a life-course model of potentially modifiable dementia risk factors in the US, JAMA Neurol. 2022 Jun 1;79(6):634. PMID: 35467745; PMCID: PMC9039828
[3] Clionsky E and Clionsky M, Dementia Prevention: Using Your Head to Save Your Brain, Johns Hopkins Press, 272 pages, April 2023.
[4] Graydon JS, et al. Ethnogeographic prevalence and implications of the 677C>T and 1298A>C MTHFR polymorphisms in US primary care populations. Biomark Med. 2019 Jun;13(8):649-661. doi: 10.2217/bmm-2018-0392. Epub 2019 Jun 3. PMID: 31157538; PMCID: PMC6630484.
[5] Shankle WR, et al, CerefolinNAC Therapy of Hyperhomocysteinemia Delays Cortical and White Matter Atrophy in Alzheimer’s Disease and Cerebrovascular Disease, Journal of Alzheimer’s Disease 54 (2016) 1073–1084 DOI 10.3233/JAD-160241
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Mitchell Clionsky, Ph.D., ABPP-CN, is a board-certified clinical neuropsychologist licensed in Massachusetts and Connecticut. He specializes in the assessment of memory disorders, other neurological diseases, mild traumatic brain injury, and ADHD.
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