Study finds that too much screentime can cause early puberty in children

By Mark Waghorn via SWNS

Smartphones and tablets are causing early puberty in children, according to new research.

The devices emit blue light which reduces melatonin - a hormone that slows sexual maturity.

They should not be used before bed, warned scientists. The chemical is secreted at night - in response to darkness.

Lead author Dr. Aylin Kilinc Ugurlu, of Ankara City Hospital, said: "We would advise 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."

The study found they also fuelled reproductive hormones - and triggered physical changes in ovaries. Worryingly, they may even trigger infertility.

Dr. Ugurlu said: "In the last 10 years, blue light sources such as tablets and phones have increased in every age group.

"Especially due to the Covid-19 pandemic, screen exposure has also increased in childhood."

It has implications for a phenomenon that has been baffling pediatricians for years. On average, girls will begin puberty around the age of 11 and boys at 12.

But there are signs they are undergoing the change a year or more sooner than decades ago.

Some girls are even developing breasts at six or seven. Obesity, chemicals, and stress have been blamed.

Now experiments have shown long periods of exposure to blue light speeds up puberty in female rats.

The time-point is roughly equivalent - relative to life expectancy. Hormonal and ovulation changes during pre-puberty and puberty are also comparable.

The findings presented at a European Society for Paediatric Endocrinology meeting in Rome are likely to apply to humans.

They could affect childhood development and future fertility. Dr Ugurlu called for further investigations.

She said: "We have found 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."

Screen time is already known to disrupt sleep in children and adults. It affects the body clock by inhibiting the evening rise in melatonin.

The hormone prepares us for rest and sleep. Levels are higher before puberty - delaying the start.

Puberty is a complex process that involves the coordination of several body systems and hormones, said Dr. Ugurlu.

Several recent studies have reported early onset for girls - particularly during the pandemic.

The link between blue light and reduced melatonin suggests increased screen time - such as during lockdowns - are playing a role in the reported increase, she said.

Dr. Ugurlu and colleagues divided immature 21-day-old lab animals into three groups of six - exposing them to a normal light cycle or six or 12 hours of blue light.

The first signs of puberty occurred significantly sooner in the latter sets. The longer the duration, the earlier the onset.

They also had less melatonin and elevated levels of oestradiol and luteinising hormone (LH). The former thicken the womb and breasts while the latter spurs ovulation.

After 12 hours of blue light, there were indications of cell damage and inflammation in the ovaries.

The researchers plan to investigate. It could have long-term impacts on reproductive health and fertility, said Dr. Ugurlu.

They will also assess if setting computers and phones to warmer 'night mode' colors such as yellow dampens the effects observed.

Dr. Ugurlu said: "As this is a rat study, we can't be sure these findings would be replicated in children."

"But these data suggest blue light exposure could be considered as a risk factor for earlier puberty onset."

Two years ago a global study found the development of breasts in girls has crept forwards by about three months per decade since the 1970s.

Dr. Ugurlu added: "Our study is the first to show the effects of blue light on puberty. We showed exposure and duration lead to early puberty."