"In fact, more grass was associated with a higher likelihood of people reporting fair to poor general health, and prevalent psychological distress," according to a statement from the Journal of the American Medical Association (JAMA) peer-reviewed medical publication on the study by University of Wollongong researchers released on Saturday.

"Though the authors note a few limitations, and this kind of study cannot prove cause and effect, the team suggest that just being around green spaces isn't quite enough, and we should be specifically investing in the tree canopy to support mental health," it said.

The study included nearly 47,000 city-dwelling adults in Australia and examined how living near different kinds of green space, including tree canopy, grass and low-lying vegetation, may be associated with risk of psychological distress, self-reported physician-diagnosed depression or anxiety, and fair to poor self-reported general health.

"No green space indicator was associated with depression or anxiety," "exposure to low-lying vegetation wasn't consistently associated with any outcome" and "exposure to more grass was associated with a higher likelihood of reporting fair to poor general health and prevalent psychological distress", the researchers reported.

Their findings were published in the JAMA Network Open online -- a monthly open access medical journal.

Limitations of the study included "self-reported health outcomes and green space availability that may have decreased in some areas over time," which means the results may "underestimated" the links, the researchers said.