Study: Light pollution can raise risk of diabetes

By Mark Waghorn via SWNS

Light pollution can raise the risk of diabetes by more than a quarter, according to new research.

Artificial light at night alters the human body clock - impairing blood sugar control, say scientists.

Street, car and shopfront lamps could have a harmful effect. It has implications for shift workers.

The discovery also has implications for people who like to use smartphones or tablets in bed.

It was based on almost 100,000 men and women in China. Those exposed to most were 28 percent more likely to develop the metabolic condition.

Lead author Dr. Yu Xu, of Ruijin Hospital, Shanghai, said: "Despite over 80 percent of the world's population being exposed to light pollution at night, this problem has gained limited attention from scientists until recent years."

The study in Diabetologia estimated more than nine million cases in Chinese adults can be attributed to it.

Evidence is growing that 24-7 lifestyles are wreaking havoc with our health by interfering with the production of melatonin.

The naturally occurring brain hormone helps regulate our circadian rhythm - protecting against illness.

Chronic exposure to residential outdoor artificial light was linked to a rise in glucose levels, insulin resistance and diabetes prevalence.

It was also associated with the poorer function of beta cells which control blood sugar by releasing insulin, a hormone stored in the pancreas.

The study used data from the China Noncommunicable Disease Surveillance Study, a representative sample of the general population across 162 sites across the country.

A total of 98,658 participants underwent interviews to collect demographic, medical, household income, lifestyle, education and family history information.

Body weight and height were measured to calculate BMI, and blood samples were taken to obtain levels of both fasting and after-meal glucose, as well as glycated hemoglobin (HbA1c).

This is a form of glucose bound in red blood cells which acts as a moving average of blood sugar over the previous eight to 12 weeks.

Participants were assigned an average artificial outdoor light exposure level for that location using satellite images. They were divided into five groups based on highest to lowest.

On average, for every 42 people living in regions with the most, there was one more case of diabetes.

Dr. Xu said: "The ubiquity of outdoor artificial light means the scale of population exposure is vast."

Its global nature is illustrated by the fact more than 99% of those in the US and Europe live under light-polluted skies.

Dr. Xu said: "Exposure to artificial light 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 kilometers from the light source."

Earth's 24-hour day-night cycle has resulted in most organisms, including humans, having an inbuilt circadian (roughly 24-hour) timing system.

It 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.

Dr. Xu said: "Our findings contribute to the growing evidence that light at night is detrimental to health and point to outdoor LAN as a potential novel risk factor for diabetes."

It has been implicated as a potential cause of metabolic dysregulation by altering the timing of food intake.

Rats exposed to artificial light developed glucose intolerance, exhibiting elevated blood sugar and insulin.

Another study found mice exposed to the nocturnal dim white light of minimal brightness for four weeks had increased body mass and reduced glucose tolerance.

This was compared to animals whose environment was completely dark at night - despite having roughly equivalent energy consumption and expenditure.

Associations have also been found between light pollution and health problems in humans.

A study of night-shift workers found those exposed to brighter light were more likely to have disrupted circadian rhythms, as well as a greater risk of coronary heart disease.

Other research found that higher light exposure was associated with a 13% and 22% increase in the likelihood of being overweight and obese, respectively.

Exposure to light in the bedroom - such as from smartphones and tablets - was reported to be positively associated with the development of diabetes in elderly people.

Dr. Xu said the diabetes epidemic has coincided with the widespread influence of light pollution.

He added: "The positive associations indicate an urgent need for countries and governments to develop effective prevention and intervention policies and to protect people from the adverse health effects of light pollution at night."