A new study published in the British Medical Journal finds a small but significant increase in psychosis risk for people who suffer the loss of a family member in childhood.

Although we know that adult health can be influenced by the genes we inherit from our parents, as well as the environment and lifestyle we experience as children, some evidence has suggested that psychological stress from the mother can also affect the development of a fetus.

But previous studies examining a link between a mother’s psychological stress and her offspring’s mental health have not been very conclusive.

This new study wanted to test this link further by seeing if children born to mothers who went through severe bereavement before, during or after pregnancy would be more likely to show symptoms of psychosis in adulthood.

The study was a large systematic review analyzing the medical records of 946,994 people born between 1973 and 1985 in Sweden.

The researchers identified mothers who had experienced the death of their parents, offspring or father of their children in a period between 6 months before conceiving and up to 13 years after giving birth. They also took into account the cause of death when bereavements had occurred in these families.

Overall, 321,249 (33%) of the children in the study experienced a family death before the age of 13.

The researchers found that 1,323 (0.4%) of these children later developed a delusional or “non-affective” psychosis (such as schizophrenia), while 556 (0.17%) of these children went on to develop an emotional disorder or “affective” psychosis (such as bipolar disorder).

By looking at when the bereavements occurred, the study concluded that mothers who suffered a bereavement before or during their pregnancy were not more likely than usual to have children who would develop psychosis.

So, it could not be proved that the psychological stress of a grieving mother can affect the future mental health of her fetus.

Dr. Kathryn Abel, lead author of the study, told Medical News Today that, despite previous studies suggesting the contrary, she was not surprised by their results:

Previous findings relating to risk of schizophrenia or other illnesses have not been very strong and often were only seen in particular groups, such as those without a history of psychosis already in the family, or only in men.”

But the researchers did measure a small increased risk of people developing psychosis who had experienced the death of a family member in their childhood.

The study found that this risk increased in people who had lost a loved one from suicide (rather than from natural causes), and the risk also increased the earlier in childhood that this death occurred.

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Of the bereaved children, 0.17% went on to develop an “affective” psychosis, such as bipolar disorder.

Although the study could identify when and how bereavements had occurred in these families, it is difficult to measure the level of psychological stress experienced by the families in the study.

Some families may have grieved for a long time, and some may have grieved comparatively little – for example, if the death was of an elderly relative who had been ill for some time – in which case, their passing may have provided some relief for the family. So some aspects of the study’s results may be subjective.

There are also a lot of other contributing childhood factors that can contribute to whether a person is more at risk of psychosis. These include socioeconomic status, neglect, abuse and bullying. These factors could also have had an effect on the results that was difficult to measure.

Also, the study only examined how experiencing a family death in childhood affects people born in Sweden. The researchers believe that further research needs to be done in non-Western and ethnically diverse populations to give us an overall picture of how grief might affect psychological development.

Dr. Abel told Medical News Today that it is possible “in non-Western populations, some societies might provide more support to bereaved families, or manage death and bereavement across society so it is less stressful and has less broad consequences on childhood.”

But Dr. Abel also mentioned that, in some societies, the opposite could be true, and “differences between risk of psychosis in those exposed and unexposed [to bereavement in childhood] could be greater.”

The researchers hope that having a better understanding of the childhood factors influencing risk of adult psychosis will ensure that “appropriately timed and appropriately resourced interventions can be developed to protect vulnerable families and children.”