A study of 60 young female students aged 17–23 in Saudi Arabia showed an association between anxiety, insomnia and natural killer (NK) cell counts[1][2][3]. NK cells form the first line of defense of the immune system, destroying virus-infected cells and abnormal cells, including cancer[1][2][3]. Among female participants, 53% reported symptoms of insomnia and 75% reported symptoms of anxiety[1][2]. Female students with symptoms of insomnia had a reduced total number and percentage of NK cells, including their subpopulations[1][2][3]. Female students with anxiety symptoms showed a lower number and percentage of circulating NK cells and their subpopulations compared to symptom-free female students[1][2][3]. Anxiety severity played a significant role: female students with moderate and severe anxiety had a significantly lower percentage of circulating NK cells[1][2][3]. The results were published in the journal Frontiers in Immunology[1][3].