A relatively large randomized control trial in Australia has shown that a text messaging program can improve not only health behaviors, but actually affect health outcomes. The 2-year study of 710 patients with coronary heart disease, published in the Journal of the American Medical Association showed that six months of a text messaging intervention produced significant reduction in cholesterol, blood pressure, and BMI and participants were also exercising more and smoking less.

"I have to say, we were pretty surprised that it worked," Clara Chow, the lead author of the study, told NPR. "These are the things that medications usually do, not text messages."

About 350 of the 700 patients in the study received text messages four times a week. The texts contained advice, motivational reminders, and support. Messages were customized to some degree based on surveys taken before the study (for instance, nonsmokers didn't receive messages about quitting smoking) but the program wasn't interactive and didn't require that users text back.

The absolute cholesterol reduction in the intervention group was 5 mg/dL, the absolute BMI reduction was 1.3, and the reduction in systolic blood pressure was 7.6 mmHg. Physical activity increased by 293 MET minutes per week. The text messages cost less than $10 per patient, and patients reported a high satisfaction with the program: 91 percent found it useful, 97 percent found it easy to understand, and 86 percent approved of the frequency of the messages.

The study adds to a gradually growing body of evidence that text messages can have a significant effect on the health of populations. A systematic review published earlier this year found that most of the text messaging interventions studied since 2009 have been effective in various areas of health.