Many of us will know what it's like to work under the harsh, artificial lighting of an office, before going home, playing on your phone with the brightness turned up, and watching Netflix in bed before sleep - but it turns out that constant exposure to bright light may not be doing our health any favours.
The brightness of lighting throughout the day could be affecting your metabolism, as well as many other bodily processes, new research has revealed.
According to a small study of 14 overweight people with insulin resistance - a sign of high diabetes risk - researchers at the Maastricht University Medical Center in the the Netherlands found lighting had a strong influence on glucose metabolism after meals, energy expenditure during sleep, and even skin temperature, which can indicate blood pressure.
The team recruited the volunteers to spend two nights in a room that measured their oxygen levels, allowing researchers to measure changes in their metabolism as they experienced a bright day with a dim evening, and a dim day with a bright evening.
The new study, published in the Diabetologia (the journal of the European Association for the Study of Diabetes), found indoor lighting that mimics the natural light-dark cycle (light during the day and dark at night) could help to alleviate adverse effects on the metabolism, caused by extended periods of exposure to artificial lighting.
The researchers found that exposure to bright light at certain times of the day can have a significant impact on post-meal glucose metabolism - which is how cells receive nourishment, in its most basic form. It also can impact thermoregulation - the body's ability to maintain its core temperature - and energy expenditure during sleep in overweight, insulin-resistant adults.
The researchers note that previous studies have shown that exposure to bright light during the evening or night is associated with being overweight or obese, as well as an increased risk of cardiovascular diseases. In the modern world, light exposure - including artificial light - is widespread and available around the clock, with most people exposed to light at home, in the workplace, or from the screens of electronic devices during the night.
The detrimental effects of light at night (LAN) include acutely elevated blood glucose and insulin levels after meals. LAN exposure is also associated with an increased incidence of type 2 diabetes mellitus in elderly people.
"Our modern society also faces a lack of sufficient time spent under bright light conditions during daytime and in fact, most time is spent indoors under artificial lighting under much lower light levels compared to natural daylight outdoors," the researchers say.
The study found that spending the day in bright light (from 8am to 6pm) led to lower blood glucose levels in the lead-up to dinner, compared to spending the day in dim light. This bright day/dim evening pattern also had a beneficial effect on energy expenditure, increasing the body's energy use during dinner.
In contrast, exposure to the dim day/bright evening condition was found to cause a reduction in energy expenditure after dinner. This cycle also heavily suppressed the release of the hormone melatonin, levels of which should rise two-to-four hours before bedtime in response to reduced levels of natural light - which plays an important role in regulating sleep cycles.
Redesigning indoor lighting in homes and offices to more closely mimic the natural light cycle "holds promise", the researchers say, and could have positive effects on the whole body, including the improvement of metabolic health - but more study is needed to fully understand the effects.
Since even small changes in energy expenditure can contribute to the development of obesity and metabolic diseases in the long-term, the authors note that more research is needed to investigate how light exposure influences the regulation of body weight and metabolism.
