Too much artificial light at night could raise the risk of type 2 diabetes by more than a quarter

Too much exposure to artificial light at night could increase the risk of getting type 2 diabetes.

More than 80 per cent of people in the world are exposed to light pollution, such as street lights shining into the bedroom, car headlights and illuminated shops and businesses.

A study has now found people in areas with high artificial light at night-time have higher blood sugar levels and react less well to insulin — the hormone which controls blood sugar.

The study of more than 98,600 people in China split them into five groups from those with the highest artificial light exposure to those with the lowest.

The group most exposed to light pollution had a 28 per cent higher rate of diabetes than the group which was least exposed.

This is likely to have mainly been type 2 diabetes, which makes up the majority of diabetes cases.

People whose body clocks are disrupted by artificial light may be at greater risk of type 2 diabetes, which is linked to obesity and poor diet, because of effects on their hunger levels and physical activity, or metabolism and body temperature.

However experts do not yet understand if this really is the case, and more research is needed.

The study, led by academics at Ruijin Hospital, which is affiliated with Shanghai Jiaotong University School of Medicine in China, concludes: ‘Our findings contribute to the growing evidence that light at night is detrimental to health, and point to outdoor light at night as a potential novel risk factor for diabetes.’

The study, published in the journal Diabetologia used satellite data which measures artificial light levels excluding the sun and moon.

Researchers looked at people living in 162 different areas, before putting them into five groups based on their light exposure.

The results suggest that for every 42 people living in the worst area for light pollution, there was one more case of diabetes which would not have happened had those people lived in the areas with the least light pollution.

Diabetes rates were worked out by looking at people who had been diagnosed with diabetes, or whose blood sugar readings showed they had the condition.

People in areas with more exposure to artificial light at night had poorer beta cell function.

Beta cells in the pancreas are important and must function well to produce insulin and control blood sugar.

Previous studies have linked high levels of artificial light at night with people being more likely to be overweight or obese, and there is some evidence it may increase the risk of breast cancer.

The study authors write: ‘People living in cities are more prone to being shifted away from nature’s 24-hour day-night rhythm towards a pattern of working around the clock, staying out late and exposure to artificial light at night.

‘It is therefore essential to assess the extent of the artificial light at night leading to or related to diabetes, so as to implement effective prevention strategies.’

The study used data from the China Noncommunicable Disease Surveillance Study, which recruited people in China in 2010, taking blood tests to determine their health.

The intensity of light for the 20 per cent of people with the highest light exposure was 69 times greater than those with the lowest light exposure.

Commenting on the findings, Dr Gareth Nye, senior lecturer at the University of Chester said more work is needed to confirm that artificial light is a trigger for diabetes, adding: ‘One issue with this study is that the areas with the highest outdoor artificial light levels are likely to be those in urban areas and bigger cities.

‘It has been known for a long time now that living in a urbanised area increases your risk of obesity through increased access to high-fat and convenience food, less physical activity due to transport links, and fewer social activities.’