(CNN) Though social media can be a helpful tool for teenagers to learn and connect with friends, experts have long warned that too much Snapchatting or Instagramming can come with downsides .

There appears to be a connection between social media use and depressive symptoms in 14-year-olds, and that connection may be much stronger for girls than boys, according to a study published in the journal EClinicalMedicine on Thursday.

"There's an alarming difference," said Yvonne Kelly, first author of the study and a professor of epidemiology and public health at University College London in the United Kingdom.

Among teens who use social media the most -- more than five hours a day -- the study showed a 50% increase in depressive symptoms among girls versus 35% among boys, when their symptoms were compared with those who use social media for only one to three hours daily.

"We were quite surprised when we saw the figures and we saw those raw percentages: the fact that the magnitude of association was so much larger for girls than for boys," Kelly said.

Yet the study, conducted in the UK, showed only an association between social media use and symptoms of depression, which can include feelings of unhappiness, restlessness or loneliness. The findings cannot prove that frequent social media use caused depressive symptoms, or vice versa.

The study also described other factors, such as lack of sleep and cyberbullying, that could help explain this association.

Explanations for the gender gap

For the study, researchers analyzed data on 10,904 14-year-olds who were born between 2000 and 2002 in the United Kingdom. The data, which came from the UK Millennium Cohort Study , included information from questionnaires on the teens' depressive symptoms and social media use.

Depressive symptoms were recorded as scores, and the researchers looked at which teens had high or low scores. They found that on average, girls had higher depressive symptom scores compared with boys.

The researchers also found that girls reported more social media use than boys; 43.1% of girls said they used social media for three or more hours per day, versus 21.9% of boys.

When examining differences between girls and boys who spend the same amount of time on social media, the researchers found the stronger association between social media use and depressive symptoms for girls.

The data showed that for teens using social media for three to five hours, 26% of girls and 21% of boys had depressive symptom scores higher than those who used social media for only about one to three hours a day.

"For both girls and boys, the more social media they use, the more likely they are to have mental health problems, but not that many studies have been able to look for the explanations why," Kelly said.

"We looked at four potential explanations simultaneously, and this is the first paper to do that. We looked at sleeping habits; experiences online, so cyberbullying; how they thought about their bodies, or their body image, and whether they were happy with how they looked; and their self-esteem," she said. "All of those four things -- the sleep, the cyberharassment, the body image or happiness with appearance, and the self-esteem -- they are all linked with the risk of having depression."

In other words, those experiences were tied to frequent social media use, which means they could play a role in the depressive symptoms. Among them, sleep and cyberbullying appeared to be the most important, Kelly said.

As for the big gender difference in the data, the study did not explore any explanations, but Kelly had some ideas.

"My best bet would be the types of things that girls and boys do online," Kelly said.

"In the UK, girls tend to more likely use things like Snapchat or Instagram, which is more based around physical appearance, taking photographs and commenting on those photographs," she said. "I think it has to do with the nature of use."

The study had some limitations, including that the findings show only a correlation between depressive symptoms and social media use, not a causal relationship.

More research is needed to determine whether teens who have depressive symptoms are more likely to use social media, versus frequent social media use leading to depressive symptoms.

Also, the data in the study was self-reported from questionnaires, which runs the risk of a 14-year-old not accurately remembering or revealing the amount of time spent playing a game or watching a video on social media.

'When it comes to depression, girls are more vulnerable'

The new study serves as "a good addition to the literature on this important topic," said Dr. Anne Glowinski, professor of child psychiatry at Washington University in St. Louis , who was not involved in the research.

"I would say that girls are, and have been for as long as measured, at a greater risk of depression than boys after puberty and that depression is a disorder which is caused by genetic and environmental, including social, determinants and their interaction," Glowinski said.

"If being online more is one of those social factors that makes the emergence of depression more likely -- as opposed to being online more representing already a symptom on the way to depression -- than it does not surprise me that there are gender differences and that girls are more vulnerable," she said. "When it comes to depression, girls are more vulnerable."

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Dr. Gary Maslow, a child and adolescent psychiatrist at Duke Health and assistant professor of pediatrics at Duke University in Durham, North Carolina, said the study finding of four factors related to social media use and depressive symptoms was interesting.

"For me, the sleep one is probably the most actionable in some ways," said Maslow, who was not involved in the research.

Among teens, "if their sleep is disturbed, and that's because they're using social media a lot, could you cut back on their social media and improve their sleep? That seems like a very tangible finding," he said.

He added that he often points his patients' families to the American Academy of Pediatrics for tips on how to establish healthy social media habits in the home.

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One tip is to set up a charging station in the home, he said, so cell phones are not charged in the bedroom, which can lead to distractions and sleep interruptions.

"Get an alarm clock, so the kid doesn't use their phone as an alarm, and really limit that nighttime usage, because we know sleep affects mood and everything else," Maslow said.

"It's a balance, because there are benefits to engagement with media. There are so many ways in which social media is important and has positive features, but there's also ways in which social media can replace social support and connection from people you are living with in person," he said. "So it's finding that sweet spot."