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It wasn’t a good year. In 2013, 10.7 million people were displaced from their homes because of conflict or persecution, according to a released last week. This brought the worldwide total of refugees to 51.2 million, the first time since the second world war that the figure has surpassed 50 million.

Children figure prominently in the UNHCR tally – half of the refugees are under the age of 18. This is especially worrying because studies drawing on data from 20th century conflicts are revealing how being on the move during childhood can have lifelong detrimental health effects.

For example, the is following more than 13,000 Finns, including people fostered as children in neighbouring countries during the 1939-40 and 1941-44 wars between Finland and the Soviet Union. This exodus allowed epidemiologists to compare the adult health of the evacuee children with the adult health of people who remained in Finland during that time.

It revealed that adults who had been evacuated as children had higher rates of coronary heart disease, and high blood pressure than those who had remained.

Height awareness

As well as having a greater risk of chronic disease when they are adults, displaced children often have developmental problems as they grow up. Anthropologist at the University of Massachusetts Boston studies people from South-East Asia’s Lao and Hmong ethnic groups now living in the US or French Guiana.

In both countries, those who were displaced as children during the Vietnam war are , a higher proportion of than those who were not displaced. Some of these characteristics are of cardiovascular disease, type 2 diabetes and high blood pressure.

Many of the adults were malnourished when they were refugees. “The earliest parts of life are when the greatest investments are made in growth, rather than in, say, reproduction. If resources are scarce at those times, it can be hard to recover that opportunity later when priorities have shifted,” says Clarkin.

Lack of food can also explain the prevalence of chronic diseases later in life. “The general idea is that an embryo or fetus faced with early malnutrition may make physiological adjustments to be better at retaining fat, in preparation for hardship” says Clarkin.

Constant stress

Data from more recent conflicts on refugee health is scarce because of the danger that . One of the few studies was by , now at the International Institute for Global Health at the United Nations University in Kuala Lumpur, Malaysia. His research focused not on refugees but on children between the ages of 3 and 5 living in Baghdad during 2009.

He found that childhood malnutrition is associated with living in an unsafe neighbourhood and the violent death of a family member within the previous five years. The combination means that the physical effects of poor nutrition and the stress of the constant danger and loss of affect these children, an experience well-known to lead to later health problems.

Both factors are relevant for young refugees, who frequently reside in camps affording poor safety and security environments, and have often lost a relative in the course of displacement.

Trying to make sure refugees don’t end up with chronic diseases for the rest of their life is not just a healthcare issue, though. “The fact that public health professionals do amazing work in tough situations should not make us lose sight of the fact that it is politicians who make the decisions that often harm lives for decades,” says Clarkin.