Most people automatically filter out spam e-mails, or delete them without ever opening them up.

But a surprising number of people actually take the time to read them, which is probably why annoying spam will continue unabated. From the New York Times’ Well, Tara Parker-Pope writes points an interesting study looking at who actually read health-related spam e-mails.

Looking at college students who were overweight, a study showed that an astounding 42 percent opened unsolicited e-mails touting weight loss products, and 19 percent actually ordered the product. And, perhaps more concerning, among those where were normal weight, 5 percent still bought what the spam was selling.

The effectiveness of spam e-mails, in this admittedly small study at least, certainly surprised me. I remember reading somewhere that it takes a success rate of 1 in 100,000 to make it worthwhile to a spam marketer.

But if they’re achieving success rates like these, it’s no wonder that the degree of spam, estimated to be 73 percent of all e-mails, will only rise.

That’s depressing.