12/18/2013 07:43 am ET Updated Jan 23, 2014

Why Do We Heed Celebrity Health Advice?

Ray Tamarra via Getty Images

There's no question that when celebrities put their name behind a cause, people hop on the bandwagon. And sometimes, it's for good -- for instance, consider the money raised for Parkinson's research by actor Michael J. Fox's foundation, or the money raised to fight HIV/AIDS by singer Sir Elton John's charity. But on the other side of the coin, celebrities can cause needless worry and even undermine the good of public health -- such as Suzanne Somers' advocacy of bioidentical hormones to supposedly reverse aging, though there's no evidence to suggest the effectiveness of such products.

So what makes us fall for celebrity health messages, even when they can be so off-base?

Researchers from McMaster University and the Harvard School of Public Health examined studies published from 1806 to today looking at why celebrity medical advice and messages seem to affect the decisions we make about our own health. The findings are published in the British Medical Journal.

The researchers found that several reasons prevailed. They include:

- The "halo effect": People generally trust celebrities, so whatever they say seems to be more credible than if someone off the street said it.

- "Herding": People think that if other people have done it, it must be true and OK to do.

- A true connection: The connection between a celebrity and product/behavior is often viewed as authentic, increasing that celebrity's credibility.

- The "cool factor": If a celebrity is doing a certain thing, people also want to do it because of the "social capital" you achieve.

"Celebrities can thereby be helpful or threaten the public’s health," researchers wrote in the study. "Their power can be harnessed to disseminate information based on the best available research evidence, or it can be abused to promote useless products and bogus treatments."

On the plus side, famous names can also hold sway for positive health behaviors. A recent study in the journal Preventive Medicine showed that when a celebrity quits smoking -- in this study's case, Brazil President Lula da Silva -- interest in smoking cessation among the general public rises dramatically.