Excess Screen Time Linked to Earlier Puberty

Kids Smartphone Glow

According to a new study, regular exposure to blue light through tablets and smartphones may change hormone levels and raise the risk of early puberty. The longer the exposure, the earlier the puberty onset.

The study found that exposure to blue light could also alter hormone levels. 

According to results from a rat study presented at the 60th Annual European Society for Paediatric Endocrinology Meeting, regular exposure to blue light through tablets and smartphones may change hormone levels and raise the risk of early puberty. Longer blue light exposure was linked to early puberty onset in female rats, which also had lower levels of melatonin, higher levels of certain reproductive hormones, and physical changes in their ovaries. Blue-light emitting mobile device use has already been related to disrupted sleeping patterns in children, but current results indicate that there may be additional hazards for childhood development and future fertility.

Blue light-producing gadgets, such as tablets and smartphones, have previously been linked to decreased sleep quality in both children and adults. This is considered to occur because blue light interferes with the evening increase in levels of the hormone melatonin, which prepares our bodies for rest and sleep. Melatonin levels are greater generally during pre-puberty than throughout puberty, which is thought to have a role in delaying the onset of puberty. Puberty is a complicated process involving the coordination of several body systems and hormones.

In recent years, several studies have reported increases in early puberty onset for girls, particularly during the COVID-19 pandemic. The link between blue light exposure and reduced melatonin levels suggests that increased screen time, such as during the pandemic restrictions, may be playing a role in this reported increase. However, it is very difficult to assess this in children.

In this study, Dr. Aylin Kilinç Uğurlu and colleagues in Ankara, Turkey, 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, 6 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 specific reproductive hormones (oestradiol and luteinizing hormone), as well as physical changes in their ovarian tissue, all consistent with puberty onset. At the 12 hours of exposure, rats also showed some signs of cell damage and inflammation in their ovaries.

Dr. Aylin Kilinç Uğurlu comments, “We have found that blue light exposure, sufficient to alter melatonin levels, is also able to alter reproductive hormone levels and cause earlier puberty onset in our rat model. In addition, the longer the exposure, the earlier the onset.”

Although Dr. Aylin Kilinç Uğurlu, cautions, “As this a rat study, we can’t be sure that these findings would be replicated in children but these data suggest that blue light exposure could be considered as a risk factor for earlier puberty onset.”

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.

The team plans to investigate the cell damage and inflammatory effects detected after longer blue light exposure since this could have long-term impacts on reproductive health and fertility. They will also assess whether the use of blue light minimizing ‘night light’ mobile device features can reduce the effects observed in the rat model.

Dr. Aylin Kilinç Uğurlu adds, “Although not conclusive, we would advise that the use of blue light emitting devices should be minimized in pre-pubertal children, especially in the evening when exposure may have the most hormone-altering effects.”

Reference: “Blue Light Exposure and Exposure Duration Effects on Rats’ Puberty Process” by Aylin Kılınç Uğurlu, Aysun Bideci, Ayşe Mürşide Demirel, Gülnur Take Kaplanoğlu, Duygu Dayanır, Özlem Gülbahar, Tuba Saadet Deveci Bulut, Esra Döğer and M. Orhun Çamurdan, 16 September 2022, 60th Annual European Society for Paediatric Endocrinology Meeting.


Introduction: In the last 10 years, blue light (BL) 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.

Methods: Immature eighteen 21-day-old female Sprague Dawley rats were divided into three groups consisting of six rats in each group: Control Group (CG), Experiment Group-1 (EG-1), Experiment Group-2 (EG-2). CG rats were maintained under standard conditions with 12/12-hour light-dark cycles . The rats of EG-1 and EG-2 were exposed to BL (450-470 nm / irradiance level 0.03 uW/cm2) for 6 hours and 12 hours, respectively. Rats were exposed to BL until the first signs of puberty and then they were euthanasiad. Serum FSH, LH, Estrodiol, testosterone, DHEA-S, leptin, melatonin were studied by ELISA method. Ovaries and uterus were dissected for histomorphological examination

Results: The medians of the pubertal entry days of the CG, EG-1, and EG-2 were 38th, 32nd, and 30th  days, respectively. (p: 0.001) A negative correlation was found between the puberty entry day of the groups and the exposure to BL and the duration of exposure. (r:-0.910, p<0.001)

The FSH, testosterone, DHEA-S, leptin levels of all groups were similar. (p> 0.05) However, LH and estradiol levels of EG-1 were higher compared CG. (p:0.027) There was a negative correlation between BL exposure, exposure time and melatonin levels (ro:- 0.537, p: 0.048)  Ovarian tissue was compatible with pubertal period in all groups. As the BL exposure time increased, capillary dilatation and edema in the over tissue increased. Prolonged exposure caused polycystic over like (PCO-like) morphological changes and apoptosis in granulosa cells.

Conclusion: Our study is the first to show the effects of BL exposure on puberty. In our study, we showed that exposure of BL and the duration of exposure lead to early puberty. PCO-like, inflammation and apoptosis were detected in the ovaries with the increase in BL exposure time.

There are studies showing that there is an increase in cases with precocious puberty and acceleration in puberty pace during the closure period compared to the pre-pandemic period. In our study, we experimentally demonstrated the effects of BL exposure on puberty and the relationship between increased exposure time.

1 Comment on "Excess Screen Time Linked to Earlier Puberty"

  1. The answer is fairly simple. If it is desired to delay the onset of puberty, forbid the rats from using smartphones and hand-held games.

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