Two major Apple investors have urged the iPhone maker to help curb smartphone addiction among children, highlighting growing concern about the effects of gadgets and social media on youngsters.

New York-based Jana Partners LLC and the California State Teachers' Retirement System said in open letter to Apple that the company must offer more choices and tools to help children fight addiction to its devices.

The two investors collectively control about $2.5 billion worth of Apple shares.

Company can play role
"Apple can play a defining role in signalling to the industry that paying special attention to the health and development of the next generation is both good business and the right thing to do," the letter said.

Among their proposals to Apple: establish a committee of experts, including child development specialists; offer Apple's "vast information resources" to researchers; and enhance mobile device software so that parents have more options to protect their children's health.

The letter cited various studies on the negative effects of smartphones and social media on children's mental and physical health.

Examples include distractions by digital technologies in the classroom, a decreased ability of students to focus on educational tasks, and higher risks of suicide and depression.

A study published in November suggested that heavy smartphone use and social media exposure among teens may contribute to depression and other traits linked with suicide.

But that and similarly designed research cannot rule out that already troubled teens may be more likely than others to be frequent users of smartphones and social media.

Worries about addictive nature of technology

The addiction issue gained notoriety when former Disney child star Selena Gomez said she cancelled a 2016 world tour to go to therapy for depression and low self-esteem, feelings she linked to a social media addiction.

Fears about smartphone addiction have already kicked off regulatory backlash. In December, the French education minister said mobile phones would be banned in schools, and draft legislation in France would require children under 16 to seek parental approval to open a Facebook account.

Even tech insiders are among the vocal critics of social media and its addictive potential.

"Apple Watches, Google Phones, Facebook, Twitter — they've gotten so good at getting us to go for another click, another dopamine hit," Tony Fadell, a former Apple executive, said on Twitter.

In its most recent update on teens and media use, the American Academy of Paediatrics said in 2016 that social media and internet use have benefits and potential risks for teens.

It urged families to create their own media use plans that include consistent time and content limits.

The American Psychiatric Association does not consider heavy internet use a true mental addiction and says more research is needed.

The investors' letter reflects growing concerns about the long-term impact of gadgets and social media, especially for those who start to use smartphones at an early age.

While tech companies have not acknowledged openly that their gadgets may be addictive, some Silicon Valley insiders have begun to speak about how gadgets, mobile applications and social media sites are designed to be addictive and to keep users' attention as long as possible.

Facebook's founding president, Sean Parker, said recently, for example, that the company exploits a "vulnerability in human psychology" to addict its users. He called its stream of comments, "likes" and reactions a "social validation feedback loop that exploits how human brains work." And, he said, "God only knows what it's doing to our children's brains".

James Steyer, the CEO of Common Sense Media, a non-profit that studies kids' technology use, called the letter a "big deal" in the ongoing effort to make it clear that cell phones are a "public health concern".

"It's the beginning of a much bigger conversation about these issues and it's great that shareholders care about it," he said.

Calls unlikely to deter investors

But some other investors said the habit-forming nature of gadgets and social media are one reason why companies like Apple, Google parent Alphabet Inc and Facebook Inc added $630 billion to their market value in 2017.

"We invest in things that are addictive," said Apple shareholder Ross Gerber, chief executive of Gerber Kawasaki Wealth and Investment Management.

He also owns stock in coffee retailer Starbucks Corp , casino-runner MGM Resorts International and alcohol-maker Constellation Brands Inc.

"Addictive things are very profitable," Mr Gerber added.

Kim Forrest, senior portfolio manager and vice-president at Fort Pitt Capital Group, agreed that companies like Facebook, Twitter Inc and Snap Inc might be more at risk than Apple if investors and regulators push back on how much time people spend on mobile devices.

"Apple is just the delivery device," said Mr Forrest, who said Fort Pitt has limited Apple holdings.

"It's only compelling with software. Software is the dopamine releaser that keeps you coming back."

Still, the investment community is increasingly holding companies to higher social standards, and there is some concern that market-leading tech companies could draw attention from regulators much like alcohol, tobacco and gambling companies have in the past.