Tony Clark, CSO and Steve Fratini, PhD
November 17, 2025
Methionine is a sulfur-containing and methyl-donating indispensable amino acid (IAA) that plays a critical role in numerous metabolic processes within the body. As one of the fundamental building blocks of proteins, Methionine is vital for the synthesis of other amino acids, hormones, and important biomolecules.
Indispensable Methionine serves as a precursor to key metabolites, including cysteine and taurine, and is involved in essential functions such as brain health, anti-microbial control, liver function, detoxification, antioxidant defense, and modulating inflammatory responses.
From the perspective of the IAA Adjusted Dietary Reference Intakes (ADRI), along with Lysine and Tryptophan, Methionine is among the scarcest IAAs available in plants, making it challenging to obtain an adequate amount of Methionine in plant-based diets (Braverman, 2012).
Methionine’s crucial actions within the body include the following:
Protein Synthesis: As an indispensable amino acid, it must be obtained from diet. It contributes to the structure and function of proteins and is specifically required for the synthesis of vital compounds like creatine and the antioxidant glutathione (Elango, 2020).
Methylation: Methionine is converted into S-adenosylmethionine (SAMe), acting as a universal methyl donor in numerous biochemical reactions. This is critical for processes like DNA methylation, which regulates gene expression--the turning of a gene’s activity up or down, inclusive of protein production (Elango, 2020) (Tzeng et al., 2016) (Struck et al., 2012).
Antioxidation: Through its role as a precursor to glutathione, methionine helps create a powerful antioxidant that protects cells from oxidative damage by neutralizing free radicals (Aquilani et al. 2023) (Rosenfeld, 2023) (Fuchs et al. 2012) (Finkel & Holbrook, 2000).
Anti-inflammation: Methionine helps regulate inflammatory responses through several mechanisms:
It helps to regulate the production of pro-inflammatory cytokines (Pérez-Cornejo et al., 2015);
It inhibits the activation of NF-kB pathway by modifying signaling therein, leading to a reduction in inflammation-inducing gene expression;
It inhibits the increase of paracellular permeability mediated by TNF-α (a chemical messenger produced by the immune system that induces inflammation), which may be related to antioxidant metabolites (e.g., taurine and glutathione) to improve intestinal homeostasis (He et al., 2018);
It regulates the formation of homocysteine, which is correlated with increased inflammation (Muller et al., 2012); and
It promotes tissue repair, which can be beneficial for cases of chronic inflammation (Braverman, 2012).
Antimicrobial: Methionine acts as an anti-microbial agent by producing sulfur compounds (e.g., cysteine, glutathione, and taurine), inhibiting the formation of biofilms, and contributing to an acidic pH in specific environments (Cai et al., 2018) (Braverman, 2012).
Methionine's multifaceted functions give it a therapeutic role in managing several health conditions.
Dementia and Cognitive Health: The global incidence of dementia is expected to reach 82 million by 2030, with nutrition, mood, and strength training among other factors, playing a key role in slowing the progression of the syndrome. In the context of nutrition, Methionine has been observed to play a key role in regulating cognitive function and mood. It does so, primarily, through its involvement in methylation processes, antioxidant defense systems, neurotransmitter regulation, neuroprotection, and mood regulation. Studies have found that Methionine levels were significantly reduced in patients with Alzheimer’s disease and frontotemporal dementia (Aquilani et al. 2023).
Cognition: Methionine participates in several metabolic pathways in the brain, including the transsulfuration pathway (TSP) and salvage cycle—which play important roles in brain health and cognitive function. Methionine’s methylation role is vital for the production of neurotransmitters like dopamine and norepinephrine, which affect cognitive processes. Its antioxidant defenses via the synthesis of glutathione protects neurons from oxidative stress, which maintains cognitive function and protects against neurodegenerative diseases (Xu et al., 2025).
Learning and Memory: Methionine is involved in acetylcholine synthesis, which is essential to learning and memory. Specifically, Methionine enables the methylation of phosphatidylethanolamine to phosphatidylcholine, a key component in cell membranes and a source of choline for acetylcholine synthesis. Acetylcholine is crucial for synaptic plasticity and its availability is correlated with improved learning capabilities via enhanced memory encoding and retrieval of memories and via improved attention and alertness, which are critical for processing new information.
Mood Disorder: By contributing to the synthesis of neurotransmitters like serotonin and dopamine, methionine may offer therapeutic benefits for individuals dealing with mood disorders such as depression (Barker et al., 2015). Studies have also found significantly reduced methionine levels in patients with Alzheimer’s disease (Aquilani et al. 2023).
Cardiovascular Disease: Methionine has implications for cardiovascular well-being. Balancing methionine with other nutrients is essential for optimizing cardiovascular health (Braverman, 2012) (Muller et al., 2012).
Methionine regulates Homocysteine—which is associated with cardiovascular disease risk and systemic inflammation.
Methionine's antioxidant and anti-inflammatory properties can help reduce oxidative stress.
Methionine plays a role in the production of nitric oxide, which is a potent vasodilator that helps to maintain blood vessel elasticity and helps to reduce hypertension; both risk factors for cardiovascular disease.
And, as a precursor to phosphatidylcholine, Methionine helps to decrease low-density lipo-protein (LDL) levels; aiding in maintenance of lipid homeostasis, to prevent plaque accumulation in arteries, which can contribute to atherosclerosis.
Liver Disorders: Research studies highlight the significance of methionine metabolism in liver health, particularly in conditions like hepatocarcinogenesis (liver cancer development). Alterations in methionine metabolism can lead to liver injury and disease progression (Tzeng et al., 2016) (Sears, 2013).
Methionine’s role in liver health is essential, particularly in the following conditions:
Liver Cancer: Glycine N-methyltransferase (GNMT) has emerged as a key player in methionine metabolism. It helps regulate the levels of S-adenosylmethionine (SAMe), a critical methyl donor in various biochemical reactions. Disruptions in GNMT activity can contribute to liver injury and may influence cancer development (Tzeng et al., 2016).
Fatty Liver Disease: Wherein it promotes fat metabolism, assisting in breaking down excess fats in the liver, which may be beneficial for individuals with non-alcoholic fatty liver disease (NAFLD) (Zhang et al., 2019).
Detoxification: Playing crucial in synthesizing glutathione, facilitating detoxification processes that minimize liver damage from toxins and oxidative stress (Fuchs et al., 2012).
Urinary Tract Infections (UTIs): Methionine can be particularly beneficial in managing urinary tract infections, primarily through its antiseptic mechanisms:
Urine Acidification: Methionine aids in acidifying urine, creating an unfavorable environment for pathogenic bacteria often responsible for UTIs (Stamm & Hooton, 1993).
Antimicrobial Properties: Through its metabolism, methionine generates sulfur compounds that may exhibit antimicrobial effects, helping to reduce bacterial populations in the urinary tract (Kumar et al., 2016).
As an adjunct treatment and not specific to UTI, methionine may complement conventional antibiotic therapy, by enhancing its effectiveness and potentially reducing the risk of antibiotic resistance (Kjeldsen et al., 2020). Pilot clinical study suggests that Methionine can play a role in the reduction of chronic bacterial prostatitis (Stamatiou et al., 2021). And, generally Methionine may provide support in the treatment of any disease involving the presence of infectious agents and the body’s inflammatory response.
Allergies: Histamine plays a central role in allergic reactions by being released from mast cells and basophils; resulting in pain and itching among other actions within the body. These actions contribute to the characteristic symptoms of allergies and highlight the importance of histamine in hypersensitivity responses. Methionine lowers blood histamine levels by increasing the breakdown of Histamine and thus may help to modulate allergic reactions (Braverman, 2012).
To ensure adequate intake, Methionine can be obtained from a variety of protein-rich foods. Higher quality protein sources of histidine include the following foods.
Animal Sources:
Beef
Pork
Lamb
Chicken
Fish
Cheese
Milk
Eggs
Plant Sources:
Tofu and soybeans
Lentils and beans (e.g., chick peas)
Nuts and seeds (e.g., chia seeds)
Methionine's crucial roles in methylation, glutathione synthesis, and cytokine (i.e., immune system) regulation underscore its impact on both acute and chronic health. By influencing these processes, it plays a part in managing inflammatory conditions such as Dementia, Cardiovascular Disease, and Liver Disease, and its antiseptic properties may aid in treating infectious diseases like UTIs. Methionine’s ability to breakdown Histamine may also help to provide allergic reactions relief.
While Methionine is generally considered safe, especially when consumed through diet, it is important to consult a healthcare professional before taking supplements or increasing the consumption of histidine rich foods. Research on dietary and supplement efficacy and potential side effects is ongoing.
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