That's what researchers at McMaster University set out to determine, and they concluded that some people can't help but follow health advice from celebrities because it's one way to be more like the people they admire.
"We seem to be hard-wired to trust famous people who may have credibility in one context and who are saying something in this different medical context," said Steven Hoffman, a health policy professor who co-wrote the article in this week's issue of the British Medical Journal.
"This can be helpful when celebrities encourage healthy behaviours, but it can be dangerous when celebrities promote something that is not backed up by science," he said. "Celebrities would be doing a greater public service if they partnered with credible medical authorities and conveyed evidence-based messages."
There are many psychological and sociological reasons people put their trust in celebrities, including the herd instinct — a tendency to make decisions based on what others have done in a similar situation, he said.
Celebrities also enjoy a "halo effect," which the researchers say gives them a "cloak of generalized trustworthiness, which extends well beyond their industry or expertise." In a bid to emulate a famous person, some people ignore information from evidence-based sources and imitate their health choices instead.
"The success or the perceived success of celebrity in one area can be generalized to all their traits and all their messages, so that someone who might be the most credible actor on screen can then be viewed as credible when giving health advice," said Hoffman.
"Of course, those two things aren't related, yet that halo effect, that golden glow of celebrity, seems to bias us into viewing them as being credible in other domains."
The researchers say high-profile celebrities can be a force for good in the realm of health promotion — think of musician Elton John's fundraising efforts for HIV-AIDS and actor Michael J. Fox's foundation to raise money for research into Parkinson's disease.
When Katie Couric had viewers of the "Today" show" follow as she underwent a colonoscopy in 2000, screening for colorectal cancer in the United States rose by 21 per cent in the next month. Actress Angelina Jolie's revelation that she had a double mastectomy after genetic testing showed she had an elevated risk of breast cancer also resulted in a big jump in public testing for the BRCA mutation.
But researchers suggest health-related messages can be misleading or downright dangerous when celebrities promote ideas or products that are not supported by science.
Couric was widely knocked for a recent episode of her talk show that dealt with girls getting vaccinated against the human papilloma virus, which can cause cervical cancer. Critics said the program was heavily unbalanced, tipped in favour of emotional anecdotes of the vaccine's purported harms and short on scientific evidence, which they said misled viewers.
But perhaps the most worrisome example of celebrity influence is Jenny McCarthy, a former model/actress who vehemently claims childhood vaccinations cause autism and other disabilities, potentially leading some parents to eschew immunizations for their children. Her claims have been disproven by rigorous scientific research.
When the outspoken McCarthy was hired in July to join "The View," Toronto's Public Health department took to Twitter to urge the ABC network to change its mind, saying her "anti-vaccine views equal misinformation." In a subsequent tweet, the agency said McCarthy cites fraudulent research and it was irresponsible to provide her with a platform on the popular daytime talk show.
"I think she's perhaps public health's nemesis No. 1," said Hoffman, "not necessarily in terms of her influence but in terms of incredulity of what she says and how much it contradicts the evidence."
"It's scary ... How is it that people come to follow someone like Jenny McCarthy's health advice when clearly she has no expertise in health issues. I mean, she's most famous for being a former Playboy model."
Dr. Natasha Crowcroft, chief of infectious diseases at Public Health Ontario, said it can be a challenge to convince some people that immunization makes kids healthier, especially in the face of vaccine opponents.
"Sometimes when I read in the papers about what some celebrities say, I get this kind of sinking feeling," Crowcroft said Tuesday, adding that anti-vaccine sentiments can "sow the seeds of doubt in people's minds, which doesn't need to be there."
But she believes most people are intelligent and understand that no matter how much they may be influenced by celebrities, the so-called beautiful people aren't necessarily the best source of advice.
"Most Canadian parents realize that if they want to know about immunization, they're better off speaking to their own doctor than they are to Jenny McCarthy."
Hoffman said medical professionals and public health advocates should utilize the power of celebrity through collaborations that could influence people's health behaviours for the better.
For instance, chef Jamie Oliver worked with the U.K. government and charities to make school meals healthier; actress Glenn Close is recognized as a mental health advocate; and model Christy Turlington released a commercial with the U.S. Centers for Disease Control urging viewers to refrain from smoking.
"We need to harness that," Hoffman said.
"When one looks at health promotion efforts, many people are quite frustrated by the lack of progress we see in influencing people's health behaviours. Certainly public health needs to learn a lesson or two from the science of celebrity."