...you can stay healthy and live longer. Hugh Wilson explains why women make the best companions

A mounting body of evidence now suggests that female friendships promote good health and longevity to an extent that male friendships do not. To put this into perspective, it's worth pointing out that all close social bonds are good for health, both male and female. As Dr Terri Apter, a social psychologist at Cambridge University and co-author of Best Friends (Random House) says: "The friendships of both sexes tend to promote health, even though they differ in style. Social connectivity - whether that's with friends, family or neighbours - increases health and longevity. The difference is that women have more friends to turn to more often, so they get more benefit."

While women tend to talk about personal issues more often and in more detail, men make light of problems or offer practical solutions. The latest research supports that observation and suggests that, at a hormonal level, women are primed to use friendships as an antidote to the ordeals and traumas of life in a way that men are not. The difference is down to a hormone called oxytocin, researchers say, which at other times helps to trigger labour, lactation, and the warm, fuzzy feeling that both sexes experience after orgasm. According to a new study by scientists at the University of California, women also release oxytocin in times of stress.

The discovery has turned 50 years of stress research - largely carried out on men - on its head. While men conform to the accepted "fight or flight" model in reaction to danger, isolation or anxiety, the release of oxytocin suggests that women can employ an altogether different strategy: they "tend and befriend". The release of oxytocin, especially in conjunction with oestrogen, encourages them to seek out and nurture relationships. As they gather friends and family around them, more oxytocin is released, creating a virtuous circle of comfort and support. In evolutionary terms, the hypothesis makes perfect sense. "Fight or flight" is a less practical option for women nursing young children than surrounding themselves with allies.

"Until this study, scientists generally believed that when people experience stress, they trigger a hormonal cascade that revs the body to either stand and fight or flee as fast as possible," says Dr Laura Cousin Klein, one of the study's authors. "It's an ancient survival mechanism left over from the time we were being chased by sabre-toothed tigers. In fact, it seems that when oxytocin is released as part of the stress response in a woman, it buffers the 'fight or flight' response and encourages her to tend children and gather with other women instead."

Scientists now believe that the "tend and befriend" model could be one of the reasons that women consistently outlive men. Men produce oxytocin, too, but while oestrogen seems to complement the performance of oxytocin, testosterone inhibits it. And in the typical fight-or-flight stress reaction, men flood their systems with testosterone. It's a reaction that takes a high physical toll. Hypertension, heart disease, mental health problems and high cholesterol are all associated with stress. The rise in oxytocin levels, on the other hand, has a calming effect on women, and mitigates the worst physiological consequences of the stress reaction. What's more, raised oxytocin levels can help wounds to heal faster and better.

But some experts fear that the health advantages conferred by the "tend and befriend" model are under threat from the pressures of modern life. "Our lives are becoming more shaped by an employment model whereby we give most of our time to our careers," says Dr Apter. "One hypothesis is that the lack of time for friendships in the modern employment model is leading to a greater incidence of heart disease among women."

Indeed, Dr Apter says that there is evidence to suggest that, in stressful workplaces, women are not as supportive of each other as they are in other circumstances. It is too simplistic, she believes, to suggest that the pressure to get on in the traditionally masculine world of work is making some women ditch their natural instincts, but working practices may be making women less able to cope with stress, and more prone to its physical consequences. As Marla Paul, author of The Friendship Crisis (Rodale) says: "Women need to spend time with friends to maintain their balance and health. Friends are not a luxury. They're essential."

If anything, these warnings serve only to reinforce the belief of a growing number of experts that strong friendships are more important to health and longevity than anyone thought. Dr Klein is unequivocal: "There's no doubt," she says, "that friends help us to live longer."