The odds of dying, for any reason, climb for those who lose parents as children, according to a new study that examined millions of people in three Nordic countries. Mortality is greatest among people whose parents died of unnatural causes, especially suicide.

These findings, published Tuesday in the journal PLOS Medicine, indicate a need for greater and longer-lasting support for children and teenagers dealing with the death of a parent, the study authors said. Indeed, the heightened death risk persisted up to two decades after bereavement. Public health professionals, they wrote, must take this information — the first of its kind — into account "when considering clinical responses and public health strategies."

Other studies have examined short-term mortality rates among children whose parents die. These have found evidence of higher death rates, particularly in developing countries, related to the provision of children's basic needs. The new investigation, led by researchers at Aarhus University in Denmark, is the first to consider data across many decades and millions of individuals.

The sample size was massive: It totaled about 7.3 million people, including everyone born in Denmark between 1968 and 2008, Sweden from 1973 to 2006, and almost everybody born in Finland from 1987 to 2007. Nordic countries, the authors wrote, are prodigious record keepers, and the extraordinary data set provided an unusually detailed account of life and death across decades.

About 189,000 people lost parents before their 18th birthday. Among these children, about 21 percent were dead within 40 years. This rate of death was 50 percent greater than people whose parents survived into their adulthood. The elevated mortality rates were apparent regardless of the sex of the parent, the sex of the child, socioeconomic background, or the cause of the parents' death. Within that group, however, it appeared the shock of unexpected death led to much higher mortality rates.

Unlike in developing countries, providing for basic needs is not behind the increased mortality because of the wealth of the countries surveyed, the authors said. What exactly is behind it is not clear, but they said several factors likely contribute. A genetic disposition for illness or mental disorders is probably a big one.

But there were other key findings: Suicide frequently begets suicide. Parent suicide also predicted risky or impaired behavior among the children. For example, children whose parents killed themselves were more likely to die in traffic crashes. One cause, they said, could be hereditary mental health problems or impulsiveness. But clearly the unexpected death of a parent, especially by suicide, resulted in the most "severe psychosocial consequences."

Children who were youngest when their parent or parents died were most at risk, probably because of a "lack of intense care ... for very young children." Their dual inability to process death and express their feelings leaves them wanting for support. And even though grief seems to subside, the study indicates health risks do not.

The authors said their paper only shows the "tip of the iceberg effects." In other words, they only looked at death, the worst possible outcome of a bad situation. Many more people struggled through depression, attempted suicide, and suffered from physical ailments — but didn't die. The social consequences of parental death in childhood "warrant the need for health and social support to the bereaved children," they wrote. And "such support may need to cover an extended time period."

Source: Li J, Vestergaard M, Cnattingius S, Gissler M, Bech BH, et al. Mortality after Parental Death in Childhood: A Nationwide Cohort Study from Three Nordic Countries. PLOS Medicine. 2014.