Artificial light at night may increase risk of diabetes

 

New study reveals that exposure to outdoor artificial light at night is associated with an increased risk of diabetes

Date:

November 14, 2022

Source:

Diabetologia

Summary:

A new study finds that outdoor artificial light at night (LAN) is associated with impaired blood glucose control and an increased risk of diabetes, with more than 9 million cases of the disease in Chinese adults being attributed to LAN exposure.

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Exposure to artificial LAN at night is a ubiquitous environmental risk factor in modern societies. The intensity of urban light pollution has increased to the point that it not only affects residents of big cities, but also those in distant areas such as suburbs and forest parks that may be hundreds of kilometres from the light source. The authors note: "Despite over 80% of the world's population being exposed to light pollution at night, this problem has gained limited attention from scientists until recent years."

Earth's 24-hour day-night cycle has resulted in most organisms, including mammals, having an inbuilt circadian (roughly 24-hour) timing system which is adapted to the natural sequence of light and dark periods. Light pollution has been found to alter the circadian rhythm of insects, birds and other animals, resulting in premature death and loss of biodiversity.

Artificial LAN has also been implicated as a potential cause of metabolic dysregulation through altering the timing of food intake. Rats exposed to artificial LAN developed glucose intolerance, exhibiting elevated blood sugar and insulin. Another study found that mice exposed to nocturnal dim white light of minimal brightness for 4 weeks had increased body mass and reduced glucose tolerance compared to animals whose environment was completely dark at night, despite having roughly equivalent energy consumption and expenditure.

Associations have also been found between artificial LAN and health problems in humans. A study of night-shift workers found that those exposed to brighter LAN were more likely to have disrupted circadian rhythms, as well as a greater risk of coronary heart disease. Other research found that higher LAN exposure was associated with a 13% and 22% increase in the likelihood of being overweight and obese, respectively, while exposure to LAN in the bedroom was reported to be positively associated with the development of diabetes in elderly people.

The potential impact of outdoor artificial LAN was revealed by a study in South India which used satellite images to map light pollution and compared this with data on general health markers among adults across the region. With increasing LAN intensity, there were corresponding rises in average body mass index (BMI), systolic blood pressure and 'bad' (LDL) cholesterol levels in the exposed population.

Diabetes is a critical public health problem in China, and the onset and progression of the disease is largely governed by behavioural and environmental risk factors. The nation's rapid urbanisation and economic growth has resulted in a dramatic increase in urban lighting, and the number of people exposed to it. Those living in cities are prone to being shifted away from a natural 24-hour day-night cycle, to one of round-the-clock working and leisure time, often staying out late and being exposed to artificial LAN.

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