Blood sugar management in type 2 diabetes is complex and usually involves a careful mix of food choices, movement and medication. New research suggests there may be one more lifestyle tweak that could support better readings: spending time by a window.
A small study published in Cell Metabolism recruited 13 people with type 2 diabetes with an average age of 70. Participants, who did not wear sunscreen, spent 4.5 days in a room where they were exposed to natural light through large windows from 8 a.m. to 5 p.m. They continued taking their usual medications and wore devices that continuously monitored their blood glucose levels.
During the day the volunteers mostly sat at a desk where they could use their phones and computers, with screens set to a low brightness. At night they were exposed to dim artificial light (similar to a lamp) and could use their devices until 11 p.m., then slept in darkness until 7 a.m.
They ate three similar meals each day, designed to maintain their current weight, and completed the same light exercise at set times across the 4.5 days.
About a month later the researchers repeated the protocol, this time in a windowless room lit only by artificial light.
When the data were compared, participants’ blood glucose levels stayed within the target range about 50% of the time during the natural light phase. In the artificial light phase they were in range about 43% of the time. The “healthy” range in the study translated to roughly 4.4 to 6.7 mmol/L. “We showed that natural daylight had beneficial effects on 24-hour glucose, with volunteers spending more time in the normal glucose range and with less variability,” says study co-author Patrick Schrauwen.
The difference is modest and the study is small, so more research is needed. Still, the findings suggest that light exposure may play a supporting role in glucose control. So why might sunlight help with blood sugar management and how can this be used day to day? Here is what doctors who treat people with diabetes want readers to keep in mind.
Why might sunlight help with blood sugar management?
The study did not explore the exact mechanism behind the effect, it simply found a link. One possible factor is vitamin D exposure from sunlight, says endocrinologis Dr Richard Siegel. He points to research suggesting that vitamin D supplementation can lower the risk that someone with pre-diabetes will progress to type 2 diabetes.
The study authors also note that light-sensitive cells in the eye may play a role. These cells help regulate metabolic activity and tend to be more sensitive to shorter wavelengths found in natural daylight. In theory, regular exposure to daylight may support healthier metabolic rhythms and blood glucose regulation. The findings “may highlight the impact of natural daylight on our metabolism,” says Schrauwen.
Weight loss surgeon Dr Mir Ali, agrees with this idea. “Sunlight plays a big role in our hormones and metabolism,” he says. “It makes sense that sunlight exposure can help the body’s metabolic processes.”
Still, Dr Siegel emphasises that this was an observational study. The researchers did not prove that natural light directly caused the change in blood sugar, only that the two were associated. Study co-author Charna Dibner adds that extended daylight exposure may also have improved evening levels of the sleep hormone melatonin, which could translate to better sleep—and good-quality sleep is known to support blood sugar management.
There are also limits to who the findings apply to. Most participants were 65 or older, so it is hard to know whether younger people with type 2 diabetes would experience the same benefit, Dr Siegel says.
How might this fit into blood sugar management?
Advice around blood sugar management does not change based on these findings, Dr Siegel says. Health authorities still recommend the following strategies:
- Track blood glucose to see what makes it go up or down
- Eat at regular times and avoid skipping meals
- Choose foods lower in kilojoules, saturated fat, sugar and salt
- Keep a record of food, drinks and physical activity
- Drink water instead of juice or soft drink
- Limit alcoholic drinks
- Reach for fruit when a sweet treat is needed
- Pay attention to portion sizes
It bears repeating: Never change a blood sugar management plan without speaking with a healthcare provider first. In other words, do not cut back on medication or other parts of treatment just because more time is spent next to a sunny window, Dr Siegel says.
Dr Schrauwen agrees. “The effects are likely too small to replace actual treatment in those already having diabetes,” he says. “Our results should be seen as another lifestyle factor that influences our metabolism and glucose homeostasis.”
The study did not report whether extra daylight exposure affected participants’ skin, even though ultraviolet light is known to increase skin cancer risk. A little sunlight is important, and sitting by a window during the day is unlikely to cause harm, but this should be viewed as a gentle add-on to an existing blood sugar management plan, not a stand-alone therapy.
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