New Delhi: Even small amount of exposure to night-time light is linked to potentially harmful changes in heart structure and function, new research shows.
“We carried out this research to find out what happens to the heart over time when people are exposed to too much light at night-time,” lead author Lu Qi, dsitinguished chair and professor at Tulane University, US, said.
The study, published in the European Heart Journal, analysed data from 11,017 participants, all of whom wore a sensor on their wrist for a week to measure levels of light exposure overnight.
Exposure ranged from near-total darkness (0 lux) to a highest of three lux, roughly equivalent to a phone screen at low brightness on a nightstand or a hallway light left on outside a cracked door.
After three years of follow-up, each participant was given a cardiovascular magnetic resonance scan to examine potential changes to the structure and function of their hearts.
“High (vs none) night-time light exposure (higher than) 3 lux was associated with left ventricular (LV) concentric hypertrophy and subclinical functional decline, including 2.4 per cent greater LV mass indexed to height (raised to power 1.7), 1.5 per cent greater mean wall thickness, and 1.9 per cent lower myocardial contraction fraction,” the authors wrote.
The results showed that participants exposed to the highest levels of night-time light saw the walls of the left chamber of their heart thicken, reducing the space inside the ventricle.
The researchers also found signs that the heart’s ability to flex during a heartbeat was reduced — an early indication of heart dysfunction.
“This is the first study of its kind, and it shows that exposure to higher levels of light at nighttime is linked to cardiac remodelling,” Qi said.
“This is where the structure and function of the heart changes, and we typically see it in response to chronic stress or injury to the heart. It’s our body’s way of adapting to that stress, but ultimately it weakens the heart and can lead to heart failure,” the lead author said.
Cardiovascular disease, including heart disease and stroke, is a leading cause of death, for which night-time light has been identified as a potential environmental risk factor.
The researchers said unlike age or genetics, night-time light exposure is a modifiable risk factor within most people’s control — involving simply turning off screens, drawing curtains before bed or sleeping with an eye mask.
“Light pollution has emerged as a new risk factor for cardiovascular disease,” Qi said.
The study, along with evidence from other studies, points to a reduced exposure of night-time light as a potential strategy for preventing heart disease by clinicians and policymakers, Qi said.
