The surprising link between sunlight and blood sugar

Now that the clocks have gone back, many Americans face a sad daily reality: ending the workday after sunset. This could be problematic for health, as sunlight benefits us in several ways. It helps regulate our internal clock, improves mood and supports the production of vitamin D, essential for bone and general health. Emerging research offers another reason to soak up the sun while you can, linking more sun exposure to improved metabolism and lower blood sugar.

“Light is an underestimated lifestyle factor when it comes to metabolism,” says Patrick Schrauwen, senior researcher at the German Diabetes Center in Düsseldorf, who has studied this relationship. “We focus on diet and exercise, but I think exposure to natural light also plays a role.”

Schrauwen was co-author of a small study, published in the January issue of Cellular metabolismin which 13 people with type 2 diabetes spent several days during work hours in one of two environments. They were either exposed to natural light through windows or only artificial lighting from 8 a.m. to 5 p.m. Continuous blood sugar monitoring showed that people spent more time in the normal blood sugar range when they had access to daylight.

“This was one of the first experimental studies to show that natural light had this effect,” says Schrauwen.

An August study of more than 420,000 people in the United Kingdom linked more exposure to the sun and lower blood sugar levels. The same study found that people who used tanning beds – which, like the sun, emit UV rays – had a significantly lower risk of developing type 2 diabetes.

The researchers used blood sugar test results from the UK Biobank, a large biomedical database, combined with satellite estimates of sunlight where participants lived, to examine whether exposure to sunlight in the days before a blood test influenced glucose levels.

“The main overall finding is that blood sugar levels were lower if you had experienced a sunnier period of weather, relative to the time of year, in the two or seven days before the test,” says Chris Dibben, study co-author and health geographer at the University of Edinburgh in Scotland.

The result was more pronounced during the winter months, says Dibben. “It makes sense that during the most sun-deprived time of year the effect is greatest,” he says.

In a separate analysis using the same medical records, Dibben and colleagues found that people who used tanning beds were less likely to develop type 2 diabetes than those who did not use them.

The researchers chose to study people who frequently use tanning beds as a sort of indicator of people who spend more time in the sun, Dibben says. In addition to receiving sunlight from the devices themselves, previous research has shown that people who use tanning beds also have more sun exposure than non-users. “They also like to tan,” says Dibben. Researchers found that people who regularly used tanning beds had about a 20% reduced risk of developing type 2 diabetes compared to non-users over their lifetime, Dibben says: “It was a pretty large effect.

Exposure to the sun and UV rays has known disadvantages. People who use tanning beds are more likely than non-users to develop skin cancer, for example. But Dibben says he was initially drawn to this area of ​​research after seeing research indicating that while people exposed to more sun had a higher risk of skin cancer, they also had an overall lower risk of dying and getting sick.

These findings are largely drawn from correlational, not causal, studies. But a growing number of studies have linked increased sun exposure to better cardiovascular health and a lower risk of obesity.

“The combination of these studies supports the idea that light is important for metabolic and cardiovascular health,” says Frank AJL Scheer, a neuroscientist at Harvard Medical School who studies how the body’s internal rhythms affect health.

Scientists are still studying how light affects metabolism, but the circadian system, which helps regulate blood sugar, body weight and cardiovascular function, is considered a major factor, Scheer says.

“If we zoom out a little bit, we know that light is the most important signal to our body clock, our circadian system,” says Scheer, who also directs the medical chronobiology program at Mass General Brigham. “Evidence from these recent studies supports the idea that daytime light is a signal that can strengthen the circadian system.”

On the other hand, too much light during the night can “disrupt this carefully coordinated system,” says Scheer, pointing to research showing how exposure to light during the night can lead to increased blood sugar levels.

“In the modern world, we live in a strange lighting environment where we’re usually indoors during the day,” a much darker environment compared to outdoors, Scheer says. “During the night, we introduce light where there was none before. We spend enormous amounts of time in front of screens – TV, phones, computers – as bedtime approaches.”

Researchers think nighttime light might activate the sympathetic nervous system, involved in the “fight or flight” response, which “is not what we should be doing at night” and could cause dysregulation of glucose metabolism, Scheer says.

Other biological pathways are also likely involved in how light affects metabolism, Dibben says. In laboratory experiments, for example, researchers have found that exposure to UVA, a type of ultraviolet light from the sun, triggers the transformation of nitrite stores in the skin into nitric oxide. Nitric oxide widens blood vessels, which could potentially lower blood pressure and increase blood flow in ways that improve glucose regulation, Dibben says.

As winter approaches and the evenings get darker earlier, Dibben says the accumulated research supports the idea that people should get outside when they can.

Scheer agrees. “Get out more during the day. If you can’t go out, position yourself near a window and reduce artificial light a few hours before and during sleep,” he advises.

Remember to use sun protection when venturing outside.