The goal of the McMaster Optimal Aging Portal is to be a trustworthy source for health information. The Portal team can see (through measuring analytics of website use) that thousands of people are using the Portal and the knowledge-sharing strategies in place (email alerts, Twitter and Facebook), with many more users added each month. Previous studies have measured the quality and trustworthiness of health information available online; others have studied the numbers and populations who use different types of information and how easy it is to use and understand. This study builds on that knowledge to find out: if easy-to-understand evidence-based messages reach members of the public, do these messages change what people know and think to do to stay healthy (in this case, what they know and think to do to lower their risk of cancer)?