Lifestyle interventions to treat or prevent type 2 diabetes and obesity are not necessarily the easiest changes to make. However, one study has found that adding a prescribed period of natural light to your day could significantly improve health markers, without any other changes.
In a small but controlled study, researchers in the Netherlands and Switzerland looked at a group of 13 participants, average age 70 years, exposed to two treatments – natural light, and artificial light – over 4.5 days. During both sessions, which were conducted on site, the participants also received the same schedule, food and physical activity allowances.
The research, presented at the annual European Association for the Study of Diabetes (EASD) in Hamburg, Germany, aims to quantify the importance of natural light for metabolic processes.
“The misalignment of our internal circadian clock with the demands of a 24/7 society is associated with an increased incidence of metabolic diseases, including type 2 diabetes,” said research leader Ivo Habets, from Maastricht University in the Netherlands. “Natural daylight is the strongest ‘zeitgeber,’ or environmental cue, of the circadian clock but most people are indoors during the day and so under constant artificial lighting."
“We were interested in whether increasing daytime exposure to natural light would improve blood sugar control in individuals with T2D,” he added.
Natural and artificial light exposure was carefully measured across the trial periods, with blood sugar levels also monitored continuously, which were followed by a suite of other metabolic tests at the end of the 4.5-day period.
On the fourth day, 24-hour substrate metabolism, resting energy expenditure and respiratory exchange ratio were measured every five hours, with blood taken to assess circulating metabolites. Core body temperature was measured around the clock.
Then, on the final half day, a fasted muscle biopsy was taken to look at circadian clock gene expression, followed by a mixed meal test (MMT), to gauge insulin production.
While not all tests showed a significant difference, the ones that did suggest natural light can be beneficial for improved metabolic function in relation to type 2 diabetes and obesity.
When participants were exposed to natural light, their blood glucose levels stayed within the normal range (4.4-7.8 mmol/L) for longer (59% of the 4.5 days vs 51% for the artificial light intervention). The respiratory exchange ratio was lower during the daylight intervention, indicating the body more easily switched from carbohydrate to fat burning as an energy source.
“We also wanted to know if it would affect their substrate metabolism or nutrient use,” said Habets. “This usually follows a 24-hour rhythm, with the body switching from using carbohydrates as its source of energy during the day, to fat at night. We'd previously shown that people at higher risk of type 2 diabetes are less able to make this switch and we wanted to find out if exposure to natural light would make the switch over easier in people who already have diabetes.”
The researchers also found that genes Per1 and Cry1, regulating circadian rhythms, were more active when triggered by natural light.
“Our research shows that the type of light you are exposed to matters for your metabolism,” Habets added. “If you work in an office in almost no exposure to natural light, it will have an impact on your metabolism and your risk or control of type 2 diabetes, so try to get as much daylight as possible, and ideally, get outdoors when you can.
“Further research is still needed to determine the extent to which artificial light affects metabolism and the amount of time that needs be spent in natural light or outdoors to compensate for this.”
The research was presented this week at the European Association for the Study of Diabetes annual meeting, with a paper to follow.
Source: Maastricht University
