A green thumb may lower your risk of cancer. Don’t believe it? You’re not the only one. Which is why a University of Colorado Boulder researcher is setting out to find hard evidence during a three-year clinical trial that will measure a variety of health factors in 312 participants who will be introduced to community gardening for the first time. “We tend to intervene from the top down,” CU Boulder professor Jill Litt said of programs to improve physical inactivity and poor diets.