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Could artificial light be making you fat? Or even worse, giving you cancer?

Artificial light

(NaturalNews) Hormone changes caused by artificial light at night (ALAN) may be partially responsible for rising global rates of obesity and cancer, according to recent studies conducted by researchers from the University of Haifa, Israel, and published in the journals Chronobiology International and the International Journal of Obesity.

"This represents the first time that anyone has shown an association between obesity and light pollution on such a large scale," researcher Boris Portnov said.

Prior studies have shown that exposure to ALAN disrupts the body's circadian rhythms and causes changes to hormone levels. In particular, ALAN appears to suppress the production of melatonin, also known as the "darkness hormone." In humans with a healthy circadian rhythm, melatonin levels naturally fluctuate, with levels lowest during the day and highest at night.

Countries with the most light are also the fattest

Previous large-scale studies have connected disrupted day-night cycles – such as night shift work – with various health problems, but few of these have focused on the effect of ALAN in the absence of sleep disruption. Meanwhile, the studies to look at the connection of ALAN have all been small, but suggestive. For example, some animal studies have found that exposure to light at night causes a reduction in metabolism.

"In recent years there are a lot of studies that use ALAN as a proxy for different health issues including obesity," said researcher Nataliya Rybnikova. "Some lab studies have examined how ALAN leads to body-mass gain among mice."

The new study was designed to look for those changes on a larger scale, in human beings.

"Melatonin is responsible for metabolic function, and ALAN also influences metabolic function in people. So we decided to check if there is an association between ALAN and body-mass gain," she added.

The researchers used nighttime satellite images of more than 80 countries to collect data on average national exposure to ALAN. They then compared this information with national obesity rates. They found a strong connection, with 70 percent of countries with high-strength lighting also having the highest rates of obesity, even after adjusting for potential confounding factors including dietary patterns, gross domestic product, percent urban population and average birthrate.

The study was not set up to determine the reason for the correlation, but the researchers suggested that ALAN may produce behavioral or physiological changes that lead to unhealthy weight gain.

Nighttime lighting also causes cancer

The researchers then also performed a similar analysis, this time looking at differences in rates of breast cancer.

Melatonin is known to possess antioxidant and anti-cancer properties, and night shift work has been linked to increased rates of cancer. Other studies by the University of Haifa researchers have shown higher rates of breast and prostate cancer in neighborhoods with higher levels of ALAN. Some of these findings are summarized in the 2013 book Light Pollution as a New Risk Factor for Breast and Prostate Cancers, authored by Portnov and co-researcher Abraham Haim.

The satellite analysis showed, as expected, that countries with higher ALAN levels also tended to have higher breast cancer rates. The connection was not as strong or consistent as it was for obesity, however. In some regions, particularly Western Europe, the connection between ALAN and breast cancer was very strong. Other regions, however, including Southeast Asia and the Persian Gulf, were characterized by "relatively low breast cancer rates against a backdrop of relatively high artificial light-at-night levels." This discrepancy suggests a potential area for further research.

The researchers also found that the quality of ALAN in the satellite photos had changed over the years. White light, such as that emitted by LEDs, has been increasing in prevalence. Disturbingly, this is the type of light most harmful to melatonin production.

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