Nikhil Prasad Fact checked by:Thailand Medical News Team May 28, 2026 42 minutes ago
Medical News: A new clinical study from researchers in Mexico has found that a simple amino acid supplement called L-citrulline may help improve blood vessel health and physical endurance in people suffering from post-COVID-19 syndrome, commonly known as long COVID. The findings are drawing attention because many long COVID patients continue to struggle with fatigue, weakness, breathing difficulties, and poor exercise tolerance months after recovering from the initial infection.
Mexican researchers find that L-citrulline supplements may help long COVID patients regain stamina and reduce blood
vessel inflammation.
The research was conducted by scientists from the Universidad Nacional Autónoma de México, the Instituto Nacional de Enfermedades Respiratorias Ismael Cosío Villegas, and the Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, all based in Mexico City.
Long COVID’s Hidden Damage
Doctors are increasingly realizing that COVID-19 is not only a lung disease. The virus can also damage the inner lining of blood vessels, known as the endothelium. This damage can continue long after the infection is gone and may contribute to inflammation, poor circulation, muscle weakness, and reduced stamina.
The researchers explained that many people with long COVID still show signs of endothelial dysfunction, a condition where blood vessels lose their ability to relax and function properly. This can reduce oxygen delivery to tissues and contribute to ongoing symptoms.
Scientists focused on L-citrulline because it helps the body produce nitric oxide, a molecule that relaxes blood vessels, improves blood flow, and supports muscle performance. Previous studies had already suggested that L-citrulline may reduce inflammation and improve vascular health in people with heart disease and hypertension.
The Clinical Trial
The randomized clinical trial involved 43 adults who had previously been hospitalized with moderate to severe COVID-19 infections. Many had serious illness during the acute phase, with over 65 percent requiring mechanical ventilation while hospitalized.
Participants were divided into two groups. One group received 4 grams of L-citrulline daily for three months along with standard nutritional care, while the control group received only nutritional treatment and routine medical care.
Researchers then tracked several health markers linked to blood vessel inflammation and physical recovery. These included ICAM-1, VCAM-1, endothelin-1, body composition, muscle strength, and a six-minute walking test used to measure aerobic capacity.
Major Improvement in Walking Ability
One of the most striking findings was the improvement in walking performance among those taking L-citrulline.
Patients in the supplement group improved their six-minute walking distance by more than 141 meters on average. By comparison, the control group improved by only about 68 meters. Researchers said the difference was statistically significant and suggested that the supplement may have h
elped restore endurance and oxygen delivery to muscles.
The scientists believe this effect may be linked to increased nitric oxide production, which can widen blood vessels and improve circulation to muscles during activity.
The study also noted that L-citrulline may help reduce muscle fatigue by supporting ammonia removal through the body’s urea cycle. This could explain why some participants experienced better physical performance despite lingering post-COVID symptoms.
Reduced Inflammatory Damage in Blood Vessels
Another important discovery involved ICAM-1, a molecule associated with inflammation and blood vessel injury. Elevated ICAM-1 levels have been repeatedly linked to chronic inflammation and endothelial dysfunction in long COVID patients.
After three months, people taking L-citrulline showed a significant reduction in ICAM-1 levels, while the control group showed almost no change. Researchers said this may indicate reduced inflammation and improved endothelial health.
This
Medical News report notes that endothelial dysfunction has increasingly become recognized as one of the major drivers behind long COVID complications, including fatigue, cardiovascular problems, and poor physical recovery.
Interestingly, other markers such as VCAM-1 and endothelin-1 did not show major differences between groups. The researchers said this suggests L-citrulline may selectively influence certain inflammatory pathways rather than producing broad changes across all vascular markers.
No Major Changes in Body Fat or Muscle Mass
Although endurance improved significantly, the supplement did not produce major changes in body composition. Researchers found no significant reductions in body fat or large increases in muscle mass during the three-month period.
Still, there were mild improvements in a measure called phase angle, which is linked to cellular health and nutritional status. Handgrip strength also improved in both groups, likely reflecting gradual recovery from severe illness.
Hope For Long COVID Recovery
The researchers concluded that L-citrulline supplementation appears to offer a promising supportive therapy for individuals dealing with long COVID, particularly those suffering from poor exercise tolerance and ongoing vascular inflammation. However, they also cautioned that the study was relatively small and conducted at a single medical center. Larger and longer-term studies are still needed to confirm the benefits and determine which patients may respond best.
Even so, the findings are important because few affordable therapies currently exist for long COVID sufferers. If future studies confirm these results, L-citrulline could eventually become part of rehabilitation programs designed to improve blood vessel function and physical recovery after COVID-19.
The study findings were published in the peer reviewed journal: Nutrients.
https://www.mdpi.com/2072-6643/18/11/1706
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