Can light levels affect your blood sugar levels and how many calories you burn?

Bright light during the day and dimmer light in the evening could help some people to better control their blood sugar levels, according to new research.

Light plays an important role in setting our internal body clock. We already know from past research that light exposure at night can affect glucose metabolism (how the body turns sugar into energy) and that it is associated with a greater risk of obesity and heart disease.

Artificial lighting is now available around the clock, with many of us looking at bright screens in the evening. Researchers at Maastricht University in the Netherlands wanted to find out if indoor lighting that more closely mimicked natural cycles of light and dark would be better for the metabolism of people who have higher than normal blood sugar levels.

To test this, they monitored 14 overweight people with raised blood sugar levels that would put them at increased risk of developing diabetes, for two 40-hour sessions in a controlled environment.

How good was the research?

The small number of participants in the study – just 14 men and women, all of whom were overweight – means that while the results are interesting, larger studies are needed before we can be confident in these findings.

A strength of the research was that they tried to keep other conditions consistent between the two sessions, so that other factors wouldn’t interfere with the findings. For example, the times of meals and what they ate were kept the same between the two sessions. Room temperature was also kept consistent, and the participants spent the same amount of time standing, sitting, and exercising. Because this was a crossover study, where the same people were exposed to different conditions, it makes it more likely that differences in findings were the result of the change in the conditions, rather than random differences between the study participants.

The study took place in specially designed chambers that could measure how much energy people burned and participants wore smart devices on their wrists to monitor their sleep patterns.

How good was the media coverage?

The study was covered by The Guardian and the Daily Express. Both articles included this quote from the researchers: “Many people live under suboptimal light conditions; often the light in their houses or offices isn’t bright enough, and they are exposed to light at night from their computers. We are quite convinced that all these factors contribute to the development of diabetes.” But this research didn’t specifically look at light from computers.

The Guardian article also said: “Based on these results, he said, people should try to boost their daytime light exposure and keep the lights dim during the evening.” But the article did not add that a study of only 14 people would not usually be considered large enough to base recommendations on.

The Guardian article did give useful background information about past research in this area, including the biological reasons why light levels can affect our health.

While the Express story helpfully included tips for how to reduce your risk of developing type 2 diabetes, it mistakenly wrote about the study as if there were two different groups of people that were monitored, saying “The other volunteer group were subjected to dim light from 8am to 6pm and bright light during the evening.” In fact, the study used the same group of people for both the bright-day-dim-night session and the dim-day-bright-night session. The Express article focused on the use of electronic devices, even though this wasn’t specifically measured by the study.

The BHF verdict

While the researchers claim they are “convinced” that light conditions contribute to the development of diabetes, more research is needed.

In the meantime, good ways to keep your blood sugar levels under control and reduce your risk of developing type 2 diabetes include sticking to a healthy diet and keeping active.