Children with depression may do worse at school because their memory is altered, a study suggests.
The mental health condition appears to affect young people's ability to remember and use information, which is crucial during exams.
Researchers have warned teachers and parents to avoid dismissing a child as lazy or not hardworking, when they, in fact, may be suffering from depression.
Statistics show that 10 percent of young people aged five to 16 have a clinically diagnosable mental health problem.
The study, involving 58 children aged between 12 and 17, tested teenagers who had high depressive symptoms with teenagers who had none or low.
The researchers, led by Jeni Fisk, a Ph.D. student at the University of Reading, looked at how well the youngsters could hold and use information to accomplish a task.
This is a measure of working memory, which is similar to short term memory in that it has a limited capacity, and the information is being processed while used - when writing a phone number down, for example.
Poor working memory skills in childhood can have an impact on children’s learning as it is required in the classroom for concentration, as well as in everyday life.
According to the study, published in Memory, the teenagers with higher depression symptoms were able to retrieve fewer specific memories and displayed less verbal fluency.
Ms. Fisk, whose research investigates the relationship between mood, memory and executive function skills in young people, told The Times: 'Poor working memory is likely to have a negative impact on school work.
'Working memory is used all of the time, every day to help us plan, to solve problems and to be organized. It is therefore very disruptive if working memory is poor.
'Working memory has also been linked to English and maths skills in young people.
'It is very important that teachers and parents are aware of this difficulty because when a young person makes mistakes it is easy to think that they are just being lazy or can't be bothered.
'If we know that they have specific problems with memory that interfere with learning, then we might be able to find ways to help. It also means that we are less likely to blame them and get angry with them for any mistakes.'
Tamsin Ford, of the Royal College of Psychiatrists, said the study's size was not large enough to find robust evidence that would influence policy changes.
However, she told The Times: 'It is another reason why we don't want to be leaving young people who are depressed without treatment because those years are so vital.
'We have effective treatments and we need to get youngsters who are depressed taking effective treatment as soon as possible.'
Figures show that young people have difficulties accessing treatment on the NHS.
Of more than 338,000 children referred to child and adolescent mental health services (CAMHS) last year, only 31 percent received treatment within the year.
The latest figures from NHS in 2017 show that one in nine children aged 5-15 have a mental health disorder, either emotional, behavioral, hyperactive, or other.
This is an increase since the last conducted survey in 2004, showing one in ten children were affected.
The figures rise to one in eight (12.8 percent) in people aged 5-19, largely driven by an increase in emotional disorders, including anxiety and depression.
People with depression, as well as stress and anxiety, have shown to have difficulty in memory tasks in previous research, and in every day life may show signs of forgetfulness or confusion.
While many studies have linked depression and loss of memory, the science to explain the relationship is nascent.
International researchers suggested that depression tends to shrink the hippocampus area of the brain, which is associated with creating new memories, storing memories and connecting them to our emotions.
Their global study of 8,927 people, published in 2015, found that people who suffer from repeated bouts of depression may be less able to form new memories.
Those who suffer chronic depression have a significantly smaller hippocampus than healthy individuals.
It's also been found that people with depression may have difficulty distinguishing between similar memories. A Brigham Young University study found in 2013 that people with depression couldn’t identify objects on a screen that were identical or similar to an object they had seen previously.
The reason behind why is unclear, but the authors wrote in the journal Behavioural Brain Research: 'It is well established that depression is associated with reduced declarative memory performance and decreased hippocampal [region in the brain] volume.'
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