Excessive Smartphone Screen Time Linked to Earlier Puberty Onset

Exposure to blue light through regular use of tablets and smartphones may alter hormone levels and increase the risk of earlier puberty, according to data from a rat study presented last month at the 60th Annual European Society for Paediatric Endocrinology Meeting in Rome.

Longer duration of blue light exposure was associated with earlier puberty onset in the female rats, which also showed reduced levels of melatonin, increased levels of some reproductive hormones and physical changes in their ovaries. Use of blue light-emitting mobile devices has previously been linked to disrupted sleeping patterns in children but these findings suggest there could be additional risks for childhood development and future fertility.

Aylin Kilinç Uğurlu, MD, of Ankara City Hospital in Ankara, Turkey and colleagues, write, “In the last 10 years, blue light sources such as tablets and phones has increased in every age group. Especially due to the COVID-19 pandemic, screen exposure has also increased in childhood. However, the effects of BL exposure in the puberty process aren’t clear. We aimed to examine the effect of BL exposure and exposure time on puberty.”

For this study, researchers used a rat model to investigate the effects of blue light exposure on reproductive hormone levels and the time of puberty onset. Female rats were divided into three groups of six and exposed to either a normal light cycle, six hours or 12 hours of blue light. The first signs of puberty occurred significantly earlier in both groups exposed to blue light, and the longer the duration of exposure, the earlier the onset of puberty. Rats exposed to blue light also had reduced melatonin levels and elevated levels of oestradiol and luteinising hormone, as well as physical changes in their ovarian tissue, all consistent with puberty onset. At the 12 hours exposure, rats also showed some signs of cell damage and inflammation in their ovaries.

The researchers note that it is difficult to mimic blue light exposure equivalent to a child’s tablet use in rats, but the time-point of puberty in rats is roughly equivalent to that of humans, if adjusted for rats’ lower life expectancy. The hormonal and ovulation changes that occur during pre-puberty and puberty in female rats are also comparable to humans. So, despite the study limitations these findings support further investigation of the potential health impacts of blue light exposure on hormone levels and puberty onset in children. 

“Our study is the first to show the effects of BL exposure on puberty,” the researchers conclude. “In our study, we showed that exposure of [blue light] and the duration of exposure lead to early puberty. [Polycystic ovary like (PCO-like)], inflammation, and apoptosis were detected in the ovaries with the increase in BL exposure time.”