The Mail Online reports on "the dark side of weight loss surgery", warning that "people who have the operation are four times more likely to commit suicide and twice as likely to self-harm". Confusingly, the headline combines two sets of statistics, from two different studies, and misreported the information on self-harm, exaggerating the risk.
The study being reported found that people who had weight loss surgery were 50% more likely (not twice as likely; that figure would be 200%) to self-harm in the three years after surgery than they were in the three years before the operation.
An older study previously showed that people having weight loss surgery were four times more likely to die by suicide than people in the general population.
Almost all the 8,815 people in the new study underwent a gastric bypass, in which a small pouch is created from the stomach, and then connected to the middle of the small intestine. Shrinking the stomach in this way means it takes less food to make people feel full.
The researchers looked at their records for the three years before and after surgery, and found that a small amount of people were more likely to have needed emergency treatment for self-harm in the years following the operation.
The research does not prove whether the operation triggered the self-harm, and reassuringly 99% of the people did not self-harm.
This was a self-matched longitudinal cohort study, comparing what happened to people in a period before and after surgery.
This type of study allows us to see if certain events were more common before or after surgery.
However, it can’t tell us why they happened, or whether they were directly caused by surgery, because we don’t know what would have happened to these people if they hadn't had their operation.
Researchers looked at the records of everyone who underwent weight loss surgery through a Canadian health insurance plan.
They searched the records for three years before and three years after participants had their surgery, investigating whether they had received emergency treatment for self-harm. They analysed the data to see whether self-harm was more common after surgery than before.
The researchers also looked at the participants’ characteristics, including their age and sex, whether they had a lower or higher income, and whether they lived in the town or countryside. They checked whether people had been diagnosed with any mental illness before their operation and whether any of these factors affected how likely people were to self-harm.
Using this information, they calculated the likelihood of people self-harming before or after weight loss surgery.
The vast majority of people did not harm themselves. Of the 8,815 people who had surgery, 111 (1.3%) self-harmed at least once, either before or after surgery. The researchers found that self-harm after surgery was about 50% more common, however.
They said there were 62 self-harm events in the three years before surgery, and 96 in the three years after surgery. Some people self-harmed several times. The average rate was 2.3 events of self-harm per 1,000 patients per year before surgery, and 3.6 events per 1,000 patients per year afterwards.
Factors such as where people lived and what they earned did not make a big difference to their chances of self-harming. Although people on lower incomes or in rural areas were more likely to have self-harmed, this was not statistically significant. However, most self-harm (93%) was by people who had been diagnosed with a mental illness before surgery.
The researchers say their results show that the risk of self-harm increased significantly after weight loss surgery. They say their findings mean doctors should assess patients’ self-harm risk carefully before they undergo surgery and should be aware of the possibility of self-harm in the years following the operation – this is in line with current UK guidelines.
They give three possible reasons for the increase in self-harm after surgery, from previous research:
They call for "active post-operative screening for self-harm risk" among weight loss surgery patients.
The headlines make this sound like an alarming study. However, there are reasons to be cautious about applying these results to UK patients.
The majority of people (98%) in the study had gastric bypass surgery. The rest had intestinal bypass surgery or sleeve gastrectomy. None had gastric band surgery, which is a reversible operation (although still serious).
In the UK, gastric bypass surgery makes up approximately half of all weight loss surgery, followed by gastric band and sleeve gastrectomy, which each account for about one quarter of all surgery. We don’t know whether the results of this study apply to people who have these other types of surgery.
It’s also important to remember that, although the risk of self-harm was higher after surgery, 99% of people in the study did not self-harm at any time. Most of the people who did self-harm had already been diagnosed with a mental illness, meaning that their chances of self-harm may already have been higher than for most people.
The years after weight loss surgery can be very difficult for some people, and the study shows they may be at higher risk of trying to hurt or kill themselves. People considering weight loss surgery need information and advice about the risks, and how to cope with the lifestyle changes after this type of operation. Doctors, friends and family should be aware that people will need support.
The study has some limitations. It does not include information about how well people’s surgery went, whether they had complications or needed repeat operations, or whether they were successful at losing weight. These things may have made a difference to their chances of self-harm.
Also, the way self-harm events were reported may have led to over-estimation or under-estimation. For example, most self-harm events were due to a medicinal overdose. For some people, this might not have been a suicide attempt, but a genuine error.
The researchers did not find records of anyone having died as a result of self-harm. However, because of the way data is reported, this might not have shown up on the records if they had not been taken to hospital before they died.
Overall, this study raises important concerns about the effect of weight loss surgery on some people’s mental health.
Weight loss surgery is no quick fix. It requires adhering to a strict set of rules (protocols) both before and after surgery, and it can impact a person’s life in a number of, often unexpected, ways.
For more information, read the NHS Choices Weight loss surgery plan