New Delhi, Jan 10 (ANI): A new research has shown for the first time that green space does appear to improve mental health in a sustained way. Mathew P. White and colleagues note that mental well-being is a major public health issue, with unipolar depressive disorder the leading cause of disability in middle- to high-income countries. Some research suggests that part of the blame for this unhappiness lies in increased urbanization - nearly 80 percent of the world's population in more developed regions live in city environments, which tend to have little room for nature. Other studies suggest a link between happiness and green space, but no research had convincingly established cause and effect of nature on well-being over time. To help fill that gap, White's team decided to examine the issue.