A new European study carried out by researchers from the UK and Belgium has found that raising a child with another person causes greater changes to the immune system than illnesses such as gastroenteritis or vaccines such as the ‘flu shot.

The study, which is the first to look at a possible association between the immune systems of two unrelated individuals who are in a close relationship, looked at the immune systems of 670 participants who ranged from 2 to 86 years of age.

The team assessed various factors over a three-year period, including age, gender, anxiety, depression, and obesity, as well as monitoring the participants' immune systems, to see which of these factors made the biggest changes to an individuals' immune system.

The researchers found that actually, the participants' immune systems did not vary much over time, returning to their original state and remaining stable even after they were forced to became more active due to a seasonal ‘flu vaccine or a case of gastroenteritis.

However their findings did show that one of the most significant factors that did change an individual's immune system was whether they lived with and raised a child with a partner. These individuals had immune systems that were more alike when compared to the diverse and different immune systems seen among the general population. In fact the immune systems between co-parents showed a 50% reduction in variation.

The team also saw that age was another key factor in shaping an individual's immune system, with a resistance to infections and response to vaccinations becoming increasingly reduced as an individual ages.

Commenting on the research, one of the study's researchers Dr Adrian Liston was not completely surprised by the findings, "Since parenting is one of the most severe environmental challenges anyone willingly puts themselves through, it makes sense that it radically rewires the immune system -- still, it was a surprise that having kids was a much more potent immune challenge than severe gastroenteritis," he said before adding, "That's at least something for prospective parents to consider -- the sleep deprivation, stress, chronic infections and all the other challenges of parenting does more to our body than just gives us grey hairs. I think that any parents of a nursery- or school-age child can appreciate the effect a child has on your immune system!"

The research is published by the leading international journal Nature Immunology.