Feeling insecure in close relationships with others may take a toll on the immune system, preliminary research suggests.

In a study of 61 healthy women, Italian researchers found that those who had difficulty establishing close, trusting relationships showed signs of weaker immune function. Specifically, lab experiments showed that the women's "natural killer" immune system cells were less lethal compared with those from other study participants.

Whether this means they're more susceptible to disease is unknown, and for now the answer to that question is a "very prudent maybe," Dr. Angelo Picardi, the study's lead author, told Reuters Health.

The findings, published in the journal Psychosomatic Medicine, are in line with research showing that chronic stress can impair immunity, and the extent of the impact may depend on how an individual perceives and responds to stress. In short, personality traits may affect immune function.

The researchers looked at the trait known as "attachment insecurity," characterized by difficulty trusting and depending on others, feeling uncomfortable with emotional intimacy or worrying about being abandoned by loved ones.

A person's "attachment style" forms in childhood, based on a child's relationship with his or her parents. It affects and is further shaped by romantic relationships later in life, explained Picardi, a researcher at the Italian National Institute of Health in Rome.

So attachment style can be seen as a fairly stable trait that affects a person's response to stressful events, according to Picardi. Attachment insecurity, he explained, affects people's ability to regulate their own emotions, including how they perceive and deal with stress -- which may affect the body's physiological response to stress.

For their study, Picardi and his colleagues recruited a random sample of female nurses, who were younger than 60 years old, had no chronic illnesses and no history of major psychiatric disorders.

The researchers measured the women's attachment style using standard questionnaires and collected blood samples to study the function of their immune system cells.

In general, the study found, women with greater attachment insecurity had lower activity in their natural killer cells, key defenders against illness.

Picardi noted that in other research, his team has found associations between insecure attachment and certain skin diseases related to immune dysfunction. These include plaque psoriasis, a condition where scaly patches form on the skin, and alopecia areata, an autoimmune disorder that causes hair loss.

"However," he said, "it should be underscored that a causal link between insecure attachment, impaired immunity, and poorer health is far away from being proved."

It's possible that relationship insecurity alone is not enough to make someone vulnerable to illness, according to Picardi, but in conjunction with other factors - like older age or chronic disease - it might be enough to worsen a person's health.

"Clearly," he said, "a lot more research is needed to elucidate these issues."