[7] For seasonal affective disorder (SAD), a randomized controlled trial (RCT) comparing high (4.5x1014 ions/second) and low (1.7x1011 ions/second) flow rate negative air ionization with bright light therapy found that the post-treatment improvement percentage was 57.1% for bright light, 47.9% for high-density ions and 22.7% for low-density ions.
[8] An older RCT conducted by the same authors also found air ionization effective for SAD.
[citation needed] The auditory stimulus, bright light, and high-density ions all produced rapid mood changes - with small to medium effect sizes - in depressed and non-depressed subjects.
[11] Researchers have continued to cite a dearth of evidence about the effects of negative air ionization.
"The presence of NAIs is credited for increasing psychological health, productivity, and overall well-being but without consistent or reliable evidence in therapeutic effects and with controversy in anti-microorganisms," researchers wrote in a 2018 article published in the International Journal of Molecular Sciences.