Numerous studies have shown how friendships can be good for our health.
The potential health benefits of romantic relationships are well documented.
A study reported by Medical News Today last year, for example, suggested that a spouse is 40-70% more likely to meet exercise recommendations if the other spouse does, while another study found that healthy lifestyle changes are more successful with partners.
But perhaps less well recognized are the wide-reaching health benefits of friendships, defined in simple terms as a mutual affection between two or more individuals.
It may not be surprising that friends are good for us, particularly when it comes to mental health; most of us have likely been through some bad times, during which friends were there to offer emotional support and help pull us through.
In fact, research has shown that people with a good support network are at significantly lower risk of depression, with one study reported by MNT last year revealing that in-person contact at least three times weekly almost halved seniors' risk of depression.
But the health benefits of friendships reach much further, as do the health risks associated with lack of companionship.
In this spotlight, we investigate the - perhaps surprising - ways in which friendship is good for us and take a look at why our pals play such an important role in health and well-being.
Your friends could be a stress-buster
Though quite possibly one of the most obvious benefits of friendship, a reduction in stress should not be overlooked.
According to The American Institute of Stress, around 3 in 4 doctors' visits are a result of stress-related illness, and stress is the basic cause of 60% of all human illness and disease.
However, a 2011 study published in the journal Developmental Psychology suggests that simply being around a good friend during a negative experience may reduce stress.
The study, which involved 103 children aged 10-12 years, found that children who spent time with a best friend throughout a negative experience had lower levels of the stress hormone cortisol in their saliva, compared with when negative experiences were endured with a parent, brother, sister, teacher or another individual.
And a new study from the University of California-Berkeley, recently published in the journal Neuropsychopharmacology, suggests that male friendships - often referred to as "bromances" - can reduce stress in bad situations.
To reach their findings, lead author Elizabeth Kirby, of the Department of Integrative Biology at UC-Berkeley, and colleagues housed male rats in the same cage.
Normally, male rats in this situation show aggression toward one another. However, the researchers found that subjecting the rodents to a moderate stressor - 3 hours of acute immobilization - actually caused them to bond.
Compared with the male rats that were housed together in an unstressed environment, those that were subject to the moderate stressor showed an increase in brain levels of oxytocin - known as the "love hormone" - and huddled more.
The team says this indicates that male friendships may alleviate the effects of stressful situations.
"A bromance can be a good thing," says Kirby. "Males are getting a bad rap when you look at animal models of social interactions, because they are assumed to be instinctively aggressive. But even rats can have a good cuddle - essentially a male-male bromance - to help recover from a bad day."
Better heart health for those with more friends
Heart disease is the leading cause of death for both men and women in the US, killing around 610,000 people in the country every year.
Frequent social interaction has been linked to better heart health.
High blood pressure is a key risk factor for heart disease and other cardiovascular conditions, including heart attack and stroke. But research has suggested that regular contact with friends could actually lower blood pressure.
A 2010 study published in the Journal of Circulation found that women who had frequent social interaction with a wide range of friends were more likely to have healthier blood pressure levels than their less social counterparts.
What is more, research has suggested that friendships can aid recovery from heart conditions.
A 2014 study published in the Journal of the American Heart Association, for example, found that patients who had experienced a heart attack were more likely to have depressive symptoms and poorer quality of life if they had low social support.
Good social networks could lower dementia risk
In the US, around 5.3 million people are living with Alzheimer's disease, of whom around 5.1 million are aged 65 and older. By 2025, the number of older adults with dementia is expected to rise to 7.1 million.
But could good social networks help stave off the illness? Some studies suggest so.
A 2008 study by researchers from Kaiser Permanente in Southern California, for example, found that women who maintained more friendships over a 4-year period were at 26% lower risk of dementia than those with smaller social networks, while those who saw friends and family daily halved their dementia risk.
Furthermore, a study presented at the Alzheimer's Association International Conference in Washington, DC, last year found that among individuals already diagnosed with dementia, loneliness was linked to 20% faster cognitive decline.
Friends could boost longevity
Given that friends could reduce stress, improve heart health and lower dementia risk, it might not come as a surprise that they could also help us live longer.
One study found stronger social relationships increased survival by 50% over a certain time period.
In 2010, Julianne Holt-Lunstad, a psychologist at Brigham Young University in Provo, UT, and colleagues analyzed 148 studies involving more than 300,000 participants, following them up for an average of 7.5 years.
They found that individuals with strong social relationships had a 50% greater chance of survival over the follow-up period than their counterparts with poor social relationships.
Additionally, the researchers found that social isolation was as bad for health as smoking around 15 cigarettes daily, being an alcoholic or not exercising. It was also found to be twice as bad for health than obesity.
More recently, a study published in the journal Psychology and Aging found that individuals who have more social interactions in their 20s may benefit from better health later in life, while better quality friendships in our 30s could help us live longer.
Why do friendships benefit health?
The stress-reducing effects of friendship have been hailed as playing a key role in the associated health benefits; it is well known that stress relief can have a positive effect on one's risk of illness.
But just as studies have shown that a spouse's lifestyle habits can influence our own health, other research shows the same can be said for friends.
A 2012 study published in PLOS One, for example, found that students who were overweight were more likely to lose weight if they socialized with lean friends, and it is well established that weight loss can lower the risk of diabetes, cardiovascular disease and other health conditions.
Other studies have suggested that our friends can also discourage poor lifestyle habits - such as smoking or unhealthy eating - that may raise our risk of disease.
However, it should be noted that the opposite is also true; friends can encourage poor lifestyle habits, which could increase the risk of bad health.
In 2007, a study published in The New England Journal of Medicine that followed more than 12,000 people over 32 years found that individuals who had a friend who became obese over a certain interval were 57% more likely to become obese themselves.
In a radio interview in 2014, Walter Willett, chair the Department of Nutrition at Harvard School of Public Health in Boston, MA, and author of the book Thinfluence, commented on this research:
"Obesity is 'contagious' but physical activity and healthy eating are, too, so we want to emphasize the latter. Invite friends to join you for a walk or for an evening of cooking healthy foods. Bring your friends along in a positive way. That is the ultimate goal."
Tips on how to make friends
While many people may be lucky enough to be able to reap the possible health benefits of friendship, for others, making and maintaining friends can be challenging.
Joining in with community activities, such as a cookery course, is a great way to make friends.
Some people may be shy, lack in self-esteem, or simply do not know the best ways to approach other people and make conversation.
In some cases, the problem may be more complex. Around 15 million adults in the US are living with social anxiety disorder - defined by the Anxiety and Depression Association of America (ADAA) as "the extreme fear of being scrutinized and judged by others in social or performance situations" - which makes developing friendships and relationships difficult.
In a report funded by the US Department of Health and Human Services (DHHS) and the Substance Abuse and Mental Health Services Administration, Mary Ellen Copeland - author, educator and mental health advocate - provides some tips on the best ways to make friends:
- Attend a support group: meeting people with similar life challenges or health problems can be a great way to make friends
- Join in with community activities: going to concerts, art shows, poetry readings, a cookery course or participating in other activities you enjoy is a good way of meeting people with similar interests
- Chat with a person about something that is of interest to both of you: this is a good way to build social ground
- Ask a person out for a coffee or to join you for a walk: this may be nerve-wracking, but it is the first step in making a new friend
- Don't bombard a new acquaintance with phone calls or texts: this can be overwhelming for the other person and might discourage them from contacting you.
But perhaps most important of all, you must make friends with yourself in order to make friends with others. As Copeland says:
"Like yourself. If you don't like yourself, don't feel that you have any value, or don't think others will like you, you will have a hard time reaching out to people who may become friends.
Work on building your self-esteem by treating yourself well - eating healthy foods, getting plenty of exercise and rest, doing things that you enjoy - and by reminding yourself over and over that you are a very special and worthwhile person."