Over the past few decades, both Type 1 and Type 2 diabetes have become far more common. Type 2 now affects hundreds of millions of people worldwide, and even Type 1, a condition usually diagnosed in childhood, is on the rise. While many blame poor diets and a lack of exercise, there might be another important factor we’re overlooking: how much time we spend indoors.

Modern life means we spend around 90% of our time inside, under artificial lighting. We move less, see less natural sunlight, and spend more time sitting. All of these changes affect how our bodies work, especially when it comes to how we handle sugar.

The Role of Sunlight in Our Health

Sunlight isn’t just about keeping us cheerful. It plays a powerful role in keeping our bodies running smoothly. It helps us produce vitamin D, which supports our immune system and helps control blood sugar levels. People who get less sun, especially in places far from the equator, tend to have higher rates of Type 1 diabetes. One study in Australia found that boys whose mothers got the most sunlight during pregnancy were 42% less likely to develop the disease.

But it’s not just vitamin D. Sunlight also includes red and infrared light, wavelengths that go beyond what our eyes can see. These kinds of light can reach deep into our skin and muscles, where they help our cells make energy. When cells make more energy, they also use up more sugar from the blood. A recent study showed that shining red light on people for just 15 minutes reduced their blood sugar levels after eating by nearly 30%.

Professor Glen Jeffery, a researcher at University College London, has been studying how light affects our mitochondria; the energy factories inside our cells. He believes that spending too much time under artificial LED lights, which are heavy in blue light but lack red and infrared, might be damaging our ability to regulate sugar. In his view, we’re becoming “red-starved,” and our cells are struggling because of it.

The Problem with Sitting Still

Alongside poor light exposure, we’re also moving less than ever before. Sitting for long periods, even if you exercise later, is harmful to your health. Muscles that aren’t used become less efficient at clearing sugar from your blood. One large study found that people who sit the most have more than double the risk of developing Type 2 diabetes.

What’s more, when we spend lots of time indoors, we’re also more likely to snack, sleep poorly, and avoid natural movement like walking or stretching. It’s a perfect storm for weight gain and insulin resistance.

Too Much Light at the Wrong Time

We’ve also changed the timing of our light exposure. Our ancestors had bright days and dark nights. Now, thanks to phones, TVs, and urban lighting, our nights are full of artificial light. Even a small amount of light, such as from a screen or bedside lamp, while sleeping, can raise blood sugar levels the next morning. It confuses our body clocks and interferes with sleep and insulin function.

Studies show that people who sleep with lights on are far more likely to develop diabetes. One Japanese study found a threefold increase in diabetes risk among older adults who didn’t sleep in darkness.

What We Can Do

The good news is that we can make changes. Even small lifestyle interventions can make a big difference. Here are some practical steps:

• Get outside in the morning – even 20 minutes of natural light can make a difference

• Move regularly – break up long sitting periods with short walks or stretches

• Reduce light at night – dim the lights in the evening and avoid screens before bed

• Try red light therapy – emerging research suggests it could support blood sugar control

• Sleep in darkness – blackout curtains or sleep masks can help.

We evolved to live in sync with the Sun. When we shut ourselves away from it, our health suffers. The rising rates of diabetes may not just be about what we eat or how much we exercise – it could also be about how much light we’re missing. Reconnecting with natural light and allowing our bodies to move and rest as nature intended may be one of the simplest ways to protect our health.

In short, our modern, indoor lifestyle could be making it harder for our bodies to handle sugar. 

Sunlight matters. Perhaps more than we ever realised.