Underscoring the importance of social media in public health, patients say friends and family are as responsible for their health as are medical professionals, according to Edelman’s 2011 Health Barometer study.

Nearly half of respondents (43%) to the global survey said that their friends and family have the biggest impact on their lifestyle with regard to health after themselves—and 36% cited friends and family as top influencers when it comes to nutrition.

Edelman’s survey of 15,000 people in 12 countries found that friends and family uniformly rank high among influencers on a range of health-related topics.

Respondents rated doctors the most credible sources of health info (88%), followed by pharmacists (81%), nurses (77%) and nutritionists (75%). Company experts placed in the middle of the pack, with 62% calling them credible—a little less than “Someone living with a disease/condition (65%)” but better than friends and family (55%). Celebs placed last (17%), followed by CEOs (22%). Reporters weren’t far ahead (29%).

The PR giant found an “action gap” in the survey data between desire to be healthier and the ability to change. More than half of respondents said they engage in at least one unhealthy behavior, and while 62% said they’d tried to change, half of them failed.

“Individuals have a powerful influence not just over their own health but also those around them,” said Edelman’s Nick Fahy, a former European Commission health official. “We must be aware of the impact that we can have.”