methionine supplementation

While methionine supplements may have several health benefits, their adverse effects must be considered. A novel study assesses the adverse effects of methionine supplementation in adults.


Methionine is an amino acid required in the process of protein synthesis within cells. As humans age and our bodies change, the metabolic rate of methionine changes as well. The amino acid has been claimed to provide biological benefits such as fighting dry skin, reducing abdominal fat, improving hair, and combating mental disorders. Although some studies have showcased improved gut function and lower risks of colon cancer, these beneficial effects largely lack scientific evidence. Methionine supplements are available, however, their adverse effects are difficult to assess. Thus, a study recently published in the American Journal of Clinical Nutrition determined the no observed adverse effect level (NOAEL) and the lowest observed adverse effect level (LOAEL) of dietary methionine supplementation in adults.

The subjects participating in the study included 15 individuals, of which 9 were women and 6 were men. All participants were between 49 and 70 years of age, in a physically healthy state, and maintained a steady body weight for 3 months. None of the subjects were diagnosed with any cardiovascular or metabolic conditions, were pregnant, or had taken any other supplementation in the days leading up to the study. A baseline blood test was conducted for all participants. Methionine supplementation was provided for a 4-week period, followed by a 2-week washout. During the intervention period, methionine supplements were administered in increasing doses. Blood samples were collected and centrifuged to isolate plasma. A questionnaire was also provided to keep track of any arising symptoms.

Methionine intake, as measured by the questionnaire, did not showcase a significant correlation with overall health and well-being, cognitive improvement, and increased tolerance in other cases. Plasma homocysteine levels were utilized as the biomarker to measure effects of methionine supplementation. Plasma homocysteine concentration increased significantly at 91 mg kg-1 d-1, establishing it as the LOAEL whereas an NOAEL was measured at 46.3 mgkg-1 d-1. Methionine supplementation had little effect on the percentage of monocytes, lymphocytes, and plasma carbon dioxide.

The results suggest that a high dosage of methionine supplementation for four weeks can cause an increase in plasma homocysteine levels. High levels of this amino acid have been linked to medical conditions such as atherosclerosis. Simultaneously, the LOAEL intake did not yield sufficient impacts on other biochemical tolerance factors. The study provides valuable data for drug developers to improve dosage and accounts for the identified adverse effect. The public, when consuming supplements, may also be cautioned to take the appropriate amount of supplementation if any is required. Further research is required to determine any other adverse effects and compare the potential benefits with possible disadvantages of methionine supplementation.

Written by Shrishti Ahuja, BSc

Study used: Tolerance to increased supplemented dietary intakes of methionine in healthy older adults

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