Blue light exposure may help improve SBP
Exposure to visible blue light at doses comparable to those achieved on a sunny day reduces systolic blood pressure (SBP) and blood vessel stiffness, leading to improved blood flow compared with control light exposure in healthy volunteers, according to a pilot study.
“Exposure to blue light provides an innovative method to precisely control BP without drugs,” said principal investigator Professor Christian Heiss of the University of Surrey, Surrey, UK.
Unlike ultraviolet (UV) light, the visible blue light has no carcinogenic potential, he clarified.
In the two-armed crossover study, 14 healthy male volunteers were randomized to whole-body irradiation with either monochromatic blue light (450 nm) or control light (with filter foil cover) for 30 minutes. This was followed by a 1-week washout period before crossing over to the other arm. Haemodynamic measures were assessed during light exposure and up to 2 hours after irradiation. [Eur J Prev Cardiol 2018;25:1875-1883]
During light exposure, blue light significantly reduced SBP by 7.9 mm Hg from baseline (p=0.005) compared with control light which had no effect.
“The effect size in our current study is … comparable or even higher than the BP-lowering effect sizes observed by typical BP-lowering medications,” wrote Heiss and co-authors who noted that mean SBP reductions were -5 mm Hg with angiotensin-converting enzyme inhibitors, -2 mm Hg with angiotensin receptor blockers, and -8 mm Hg with calcium antagonists (-8 mm Hg) as reported in a previous study. [Lancet 2003;362:1527-1535]
Although SBP readings returned to baseline after light irradiation was stopped, the values remained lower than the control arm which saw elevated SBP that did not return to baseline during the observational period. The authors proposed might be due to stress related to long hour in a supine position during the study and application of filter foil during control irradiation.
There was no significant difference in diastolic BP response between the two groups.
In addition, forearm blood flow and flow-mediated dilation were increased while pulse wave velocity and forearm vascular resistance were decreased during blue light exposure compared with control light (p<0.05 for all), with the changes persisting throughout the 2 hours observation period after light exposure.
In search of possible mechanism mediating the effects of blue light on the haemodynamic changes observed, the researchers found that plasma levels of NOx (13 vs 4 µmol/L; p=0.043) and circulating NO stores (RXNO; 3 vs 0 nmol/L; p=0.046) rose significantly at the end of exposure to blue vs control light.
“Our data suggest that whole-body blue light irradiation can release NO from photolabile NOx in the skin into the circulating blood where they mediate clinically relevant haemodynamic effects including lowering of SBP potentially by decreasing large artery stiffness and resistance artery dilation,” they explained.
“[These findings] encourage the development of devices for intermittent blue light application to improve vascular function as a supportive strategy to pharmaceutical approaches,” said Heiss and co-authors. “Wearable blue light sources could make continued exposure to light possible and practical. This would be particularly helpful to those whose BP is not easily controlled by medication, such as older people.”
They suggested that the potential of blue light in CVD prevention should be evaluated in a wider population, including healthy men and women as well as patients at high risk for CVD.