Still considered a rite of passage by some, research is now attempting to understand why victims of childhood bullying are at risk of poorer outcomes in adulthood, not only for psychological health, but also physical health, cognitive functioning and quality of life.

Though there is no universal definition of childhood bullying, the term is often used to describe when a child repeatedly and deliberately says or does things that causes distress to another child, or when a child attempts to force another child to do something against their will by using threats, violence or intimidation.

The US Department of Health & Human Services (DHHS) quote studies that show the most common types of bullying are verbal and social:

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Research shows that persistent bullying can cause depression and anxiety and contribute to suicidal behavior.
  • Name calling - 44.2% of cases
  • Teasing - 43.3%
  • Spreading rumors or lies - 36.3%
  • Pushing or shoving - 32.4%
  • Hitting, slapping or kicking - 29.2%
  • Leaving out - 28.5%
  • Threatening - 27.4%
  • Stealing belongings - 27.3%
  • Sexual comments or gestures - 23.7%
  • Email or blogging - 9.9%

The health impact of bullying on children is complex. Research shows that persistent bullying can cause depression and anxiety and contribute to feelings of suicidal behavior.

The DHHS, however, says that media reports often "oversimplify" the relationship between suicide and bullying. Most young people who are bullied do not become suicidal, they state, and most young people who die by suicide have multiple risk factors, beyond bullying alone.

As well as the psychological impact of bullying, though, studies have shown that children who are bullied may also be prone to physical illness, not only during the period in which the bullying took place, but in later life.

For instance, recently Medical News Today reported on a study that found children who are bullied between the ages of 8 and 10 are more likely to experience sleepwalking, night terrors or nightmares at the age of 12.

Victims of bullying have 'poorer health, lower income, lower quality of life' as adults

But other research shows that the long-term health effects of bullying on the victim are potentially much more far-reaching and serious.

Fast facts about bullying
  • Over 77% of American students have been bullied verbally, mentally and physically
  • About 85% of incidents receive no kind of intervention, so it is common for bullying to be ignored
  • In surveys quoted by the DHHS, approximately 30% of young people admit to bullying others.

A 2014 study from researchers at King's College London in the UK found that the negative social, physical and mental health effects of childhood bullying are still evident up to 40 years later.

The study examined data from the British National Child Development Study, which includes information from all children born in England, Scotland and Wales during 1 week in 1958. In total, 7,771 children from that study - whose parents provided information on their child's exposure to bullying when they were aged 7 and 11 - were followed until the age of 50.

Similar to modern rates in both the UK and US, 28% of children in the study had been bullied occasionally, and 15% had been bullied frequently.

The researchers found that, at age 50, participants who had been bullied when they were children were more likely to be in poorer physical and psychological health and have worse cognitive functioning than people who had not been bullied.

Victims of bullying were also found to be more likely to be unemployed, earn less and have lower educational levels than people who had not been bullied. They were also less likely to be in a relationship or have good social support.

People who had been bullied were more likely to report lower quality of life and life satisfaction than their peers who had not been bullied.

Even when factors such as childhood IQ, emotional and behavioral problems, parents' socioeconomic status and low parental involvement were taken into account, the association remained between bullying and negative social, physical and mental health outcomes.

"Our study shows that the effects of bullying are still visible nearly 4 decades later," said lead author Dr. Ryu Takizawa, from the Institute of Psychiatry at King's College London. "The impact of bullying is persistent and pervasive, with health, social and economic consequences lasting well into adulthood."

"We need to move away from any perception that bullying is just an inevitable part of growing up," added co-author Prof. Louise Arseneault. She says that while programs to stop bullying are important, teachers, parents and policymakers need to focus efforts on early intervention to prevent problems caused by bullying persisting into adolescence and adulthood.

How does bullying in childhood affect physical health in adulthood?

Prof. Arseneault has also written in depth on another 2014 study into the long-term health effects of bullying, conducted by a team from Duke University Medical Center in Durham, NC.

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Some experts think that bullying results in a kind of "toxic stress" that affects children's physiological responses, possibly explaining why some victims of bullying go on to develop health problems.

That study investigated the hypothesis that bullying victimization is a form of "toxic stress." Proponents of this theory suggest that this toxic stress affects children's physiological responses, which may explain why many - otherwise healthy - victims of bullying go on to develop health problems.

One mechanism that may drive this psychological and physical relationship is the inflammatory response, which occurs when the body is fighting an infection, reacting to an injury or responding to a chronic health problem.

The Duke team assessed the extent of this response in victims of bullying by measuring levels of a protein called C-reactive protein (CRP). High levels of CRP occur during the inflammatory response.

Previously, studies have shown that people who were abused by an adult in their childhood display elevated levels of CRP. Prof. Arseneault says this suggests that the body is reacting to toxic stress in the same way as when it is attempting to fight an infection.

The Duke team analyzed data from the Great Smoky Mountains Study which measured CRP levels in 1,420 children aged 9-16 who had been victims of bullying, as well as bullies and "bully-victims" - children who are victims of bullying and who also bully others.

The researchers found that children who had been involved in bullying multiple times - whether as victims, bullies or bully-victims - had higher levels of CRP than those who were not exposed to bullying.

The team then looked at the participants' CRP measurements as they entered adulthood. The findings were similar - people who had been repeatedly bullied during childhood displayed the highest levels of CRP.

However, in a finding that surprised the researchers, participants who bullied others were found to now have the lowest levels of CRP out of all groups studied - including those who had not been exposed to bullying.

For both the childhood and early-adulthood CRP measurements, the researchers took into account factors such as maltreatment, family dysfunction, anxiety disorders, prior CRP levels and variables associated with CRP, but the associations remained.

Prof. Arseneault comments that previous research along these lines has demonstrated that bullying can influence physiological responses to stress, including altered levels of cortisol, the hormone that is released in the body when under stress. One study involving pairs of identical twins - where one twin had been bullied and the other had not - found that the bullied twins demonstrated a "blunted" level of cortisol response.

Medical News Today spoke to lead author of the study, William E. Copeland, assistant professor at the Center for Developmental Epidemiology at Duke, who confirmed that the elevated CRP levels suggest one mechanism responsible for translating the act of bullying into potentially long-term physical health problems:

"Bullying and the continued threat of being bullying can have physiological consequences. There is evidence that over time this experience can dysregulate biological stress response systems. In our work, victims have higher levels of the inflammatory marker C-reactive protein up to a decade after their bullying experience. Over time, the wear and tear of these physiological changes can limit the individual's ability to respond to new challenges and put them at increased risk for physical illnesses."

Victims, bullies and bully-victims - how do their outcomes compare?

In 2013, Prof. Copeland also co-authored another analysis of data from the Great Smoky Mountains Study, looking into the long-term health consequences of bullying that - as wth the King's College London study - found that victims of bullying have a higher risk of poor health, lower socioeconomic status and problems with forming social relationships as adults.

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"Bully-victims" were found to be six times more likely to have a serious illness, smoke regularly or develop a psychiatric disorder in adulthood than those who had not been involved in bullying.

This study also looked at the victims, bullies and bully-victim groups. However, in this study, the bully-victims were found to be the most vulnerable group. Subjects in this group were found to be six times more likely to have a serious illness, smoke regularly or develop a psychiatric disorder in adulthood than those who had not been involved in bullying.

"Not all victims are created equally," Dr. Copeland says of the study's findings. "Victims that attempt to fight back and hurt others tend to be impulsive, easily provoked, have low self-esteem and are often unpopular with their peers. Bully-victims are also more likely to come from dysfunctional families and to have been maltreated by family members."

"As such," he continues, "these children have been exposed to high levels of adversity and lack the skills, temperament and social support to cope effectively. This puts them at profound risk for long-term problems."

The 1,420 participants were interviewed at ages 9, 11 or 13, and then followed up at ages 19, 21 or 24-26 years. Nearly a quarter of the children (23.6%) reported having been bullied, with 7.9% saying they had been bullies, and 6.1% reporting that they had been bully-victims.

While both victims and bully-victims were found to be at risk of poorer health, finances and social relationships as adults, participants who reported being bullies had no association with poorer outcomes in adulthood.

However, Dr. Copeland told us that:

"It is important to be clear here that bullies do not get off scot-free. Pure bullies do have worse outcomes in adulthood but those poor outcomes tend to be due to their preexisting behavior problems and family adversities rather than being a bully per se. For victims, in contrast, the experience of being a victim itself is associated with worse outcomes."

Dr. Copeland considers that the most effective prevention programs involve parent meetings, firm disciplinary methods and strong supervision.

"Once a child has been bullied, it is critical for parents and teachers to be supportive and to ensure that the bullying does not continue," he emphasizes. "Too often, bullying is not taken seriously and is treated like a normal rite of passage."

Though evidence is mounting for physical health problems in adulthood that are associated with childhood bullying, experts say it is the psychological consequences that remain the most concerning, and which are preventable.

Victims of bullying are at increased risk for a range of anxiety disorders, says Dr. Copeland, while bully-victims are at risk for depression and suicide.

"This is tragic because we have effective, tested treatments for all of those problems," he says. "The problem is that very few people with such mental health problems get the help they need."