FORTUNE – Are you too busy to stop by your colleague's office to chat or go to lunch? Or are you someone who keeps work relationships strictly business? Be warned: If you're not reaching out to make and nurture friendships at work, you're probably hurting your career.
Recent research finds that people who initiate office friendships, pick up slack for their co-workers, and organize workplace social activities are 40% more likely to get a promotion in the subsequent two years. "How much you give at work directly affects how much you get at work," says Shawn Achor, author of The Happiness Advantage: The Seven Principles of Positive Psychology That Fuel Success and Performance at Work.
In his research, Achor divides individuals into quartiles based on how much they provide this kind of social support to colleagues. Work altruists, the top 25%, give the most, while work isolators, the bottom 25%, provide the least. Work altruists report significantly higher job satisfaction and feel 10 times more engaged by work than people in the lowest quartile.
So not only do these uber-connectors benefit from their behavior, the employer gains as well. "Happiness is the greatest competitive advantage in the modern economy," Achor says. "If you can find a way of creating happiness at work, you're 31% more productive, your sales are 37% higher, people perceive you as being more charismatic and you're three times more creative."
To increase social support, Ochsner Health System, a large Louisiana health care provider that Achor works with, implemented an approach called the "10/5 Way." After educating 11,000 employees about the importance of offering support to each other, Ochsner asked employees to make eye contact and smile whenever they walk within 10 feet of another person in the hospital. If they pass within 5 feet, they say hello.
Since then, Ochsner has seen a 5% increase in patients' likelihood to recommend the organization, greater unique patient visits, and a significant improvement in overall patient satisfaction. "We can change the social script very easily by making some small adjustments," Achor says.
Social support also improves the health of individuals. People who receive high levels of social support are as likely to live longer as those who exercise regularly, and low social support does as much damage as high blood pressure. A 2007 study of 1,648 Harvard students found that social support was the best predictor of happiness in periods of high stress, with a correlation of .71, according to Achor. That's a stronger tie than the link between smoking and cancer, which is .37.
Researchers investigating the effects of social support are part of the larger positive psychology movement, which stresses the ability of individuals to change their own level of happiness -- and related positive life outcomes. Participants in one of Achor's studies were asked to take daily steps to build positivity, such as writing a positive message to someone in their social network or writing down three things they were grateful for over the course of three weeks. Individuals' mean score on the life satisfaction scale -- a metric widely accepted to accurately predict productivity and happiness at work -- moved from 22.96 before the training (on a 35-point scale) to 27.23 four months later.
But before you start inviting colleagues to lunch, dinner, and happy hour, take a moment to understand the importance of context. Look at how people in your organization create and deepen friendships.
"Feeling like you're connected to someone else makes a difference, it's the root of happiness," says George Bradt, a consultant and author of The New Leader's 100 Day Action Plan. Still, "if you go into an organization and start inviting people to lunch in a place where people don't do lunch, you're in trouble."
For instance, a manager at a large Swiss bank moved to the company’sAustraliaoffice and wanted to make a good impact by inviting everyone to a dinner meeting at 7 or 8 p.m. The team actually refused, saying, "We're done by 5." "That leader had to completely change his leadership style," Achor recalls.
"In some organizations, inviting your direct reports out for drinks after the workday is a good thing," Bradt agrees. "In others it's an insult because you're making them drink and taking them away from their family. You have to take them out for coffee in the morning or lunch."
You can learn about an organization's culture by asking questions about how people interact, but you must also observe whether the answers to those questions are accurate, he says. Over time, a determined leader can shift the culture to being more socially supportive overall.
When in doubt, you can always begin by offering professional support to colleagues. "As soon as you start asking people to meet up with you or helping people with their work, you change the social script," Achor says.
Women in male-dominated industries are particularly at risk of being socially isolated at work, notes Michelle Friedman, a professional development coach based in theNew York Cityarea. "The ones who feel isolated ... suffer in terms of engagement and productivity," Friedman says.
Some mothers, for instance, resist talking about their kids at work for fear of being typecast or discounted, which keeps them from truly connecting with co-workers.
"Workplace bonds generally form around things that people have in common. It can be working on a project together or if you're on a case or deal together," she says. "The deeper bonds I've seen are where you feel the bond is with the whole person; it's not just on the professional level."
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