There is no direct link between prison suicides and overcrowding in jails, a study of almost 4,000 deaths has found.
Psychologists examined suicides from 24 countries including England and Wales, following fears that prisoner numbers were contributing to the high rate of suicide.
The research, published in the Lancet Psychiatry journal, found that a range of issues such as access to mental health care and the amount of daily activity could be more important risk factors.
After examining 3,906 suicides across 20 European countries, as well as the US, Canada, Australia and New Zealand, it found deaths were highest in countries with the lowest rates of incarceration.
The study said: “Most of the examined prison-level factors were not associated with prison suicide rates, suggesting that prison suicides are likely to be the result of a complex interaction of different factors, and not merely due to the prison environment.
“Studying these factors within countries could be informative, and their interaction might also provide some explanation.”
It concluded there were “no simple ecological explanations for prison suicide” and called for national strategies to address the problem.
Nordic countries had the highest prison suicide rates, with more than 100 per 100,000 prisoners. Denmark’s rate was slightly lower, with 91 per 100,000.
In western Europe, rates in France and Belgium were also more than 100 per 100,000 inmates.
Australia, New Zealand and North American countries had ranges of 23 to 67.
Out of the 3,906 deaths, 93% were male and 7% female.
The research was prompted by concerns that overcrowding was contributing to the disproportionately high levels of suicide in prisons, with 119 out of 205 countries reportedly exceeding their prison capacity.
In England and Wales, suicide rates are five or six times higher than among the general population.
But the research found no clear link between suicides and prison overcrowding, except in low-income countries where extreme overcrowding might cause extra stress.
It even suggested overcrowding could mitigate the risk of suicide as vulnerable prisoners were less likely to be left alone as so many cells designed for single use were in double occupation.
But the research found a lack of detailed data on conditions in prisons and the individual prisoner’s circumstances that may have contributed to their decision to take their own life.
Researchers said: “Prison suicides are likely to be the result of a complex interaction of different factors, and not merely due to the prison environment.”
They argued that “more sensitive markers of health care need to be routinely recorded” to understand the high suicide rate in prisons, including how many people are engaged in active mental health treatment, and the extent and quality of prison care.
They also made the case for better recording of “ecological factors” in prisons, such as assault rates, levels of self-harm, the amount of daily meaningful activity, and access to employment or training.
Factors such as access to ligature points were also rarely recorded, the researchers found.
The Prison Reform Trust has long blamed overcrowding for unsafe conditions in prison. In a statement in October in response to an increase in self-harm and assaults in prison, a spokesman for the charity said: “Too many prisoners are held in overcrowded and impoverished conditions with too few staff to provide a safe and constructive regime.”
In response to the new research, the Prison Reform Trust’s director Peter Dawson said: “This useful research shows that reducing suicides in prison is complex.
“But we know in this country that between 2008 and 2014 the situation was improving before deteriorating sharply as staffing levels were drastically reduced.
“Good procedures and good relationships underpin every aspect of safety in prison – overcrowding is just one of the reasons both are under pressure. Tackling it is long overdue and vital to prisons delivering every aspect of the Government’s many ambitions for reform.”