Kirin Study Finds L-Citrulline May Improve Vascular Endothelial Function and Shoulder or Lower Back Discomfort in Middle-Aged and Older Adults with Elevated Blood Pressure

Kirin Holdings’ Health Science Research Institute and Matsuyama University conducted a clinical study focusing on vascular aging in middle-aged and older adults, evaluating the effects of L-citrulline intake on vascular function. The study found that healthy middle-aged and older adults with elevated blood pressure showed improvements in vascular endothelial function after taking L-citrulline, along with improvements in subjective symptoms such as stiff shoulders and lower back pain. The findings will be presented at the 80th Annual Meeting of the Japanese Society of Nutrition and Food Science, held from May 15 to 17, 2026, and have also been accepted by the international academic journal Nutrition Research. L-citrulline is an amino acid found in large amounts in plants of the gourd family and is expected to help improve blood flow and maintain vascular flexibility. In this study, elevated blood pressure refers to clinic blood pressure of 130–139 mmHg / 85–89 mmHg. Although this does not meet the definition of hypertension, it is considered a stage associated with higher future risk of hypertension and cardiovascular disease, where lifestyle improvement is recommended. As society continues to age, extending healthy life expectancy and improving quality of life are becoming increasingly important. Aging does not occur through the decline of just one part of the body, but through the gradual deterioration of multiple fundamental biological functions. Therefore, reducing risks to these foundational health functions is important. Maintaining healthy vascular function is particularly significant because it is linked not only to the circulatory system, but also to cognitive function, kidney function, motor function, mood, and overall health. The study enrolled 66 healthy men and women aged 45 to 70 with reduced vascular function. It was conducted as a randomized, double-blind, placebo-controlled, parallel-group trial. Participants consumed either a test food containing 3,000 mg of L-citrulline per day or a placebo food without L-citrulline for 12 weeks. Evaluations were conducted before intake, at week 6, and at week 12. Evaluation items included flow-mediated dilation, or FMD, as an indicator of vascular endothelial function; blood levels of 3-nitrotyrosine, a factor associated with the promotion of arteriosclerosis; and subjective symptoms such as lower back pain and stiff shoulders. Subjective symptoms were assessed using a visual analogue scale, where participants marked their current symptom level on a 10 cm line and the distance from the left end was quantified. Among participants who had elevated blood pressure at baseline, 12 weeks of L-citrulline intake significantly improved FMD compared with the placebo group, indicating improved vascular responsiveness to changes in blood flow and better vascular flexibility. In the same subgroup, changes in lower back pain and stiff shoulder symptoms also improved significantly compared with placebo. Blood 3-nitrotyrosine levels likewise showed significant improvement compared with placebo. The study suggests that continuous intake of L-citrulline may help improve vascular function and physical condition in healthy middle-aged and older adults with elevated blood pressure. Kirin Group stated that it will continue to advance research on vascular function and anti-aging to help address health challenges, while contributing to a more fulfilling society through product development focused on nature and people.