Research has established that low-income people tend to have higher mortality rates than high-income residents. This study across all of England demonstrates that this gap in mortality rate is about half the size in areas with the most green space compared to areas with the least green space.
Mitchell, R. and Popham, F., 2008. Effect of exposure to natural environment on health inequalities: an observational population study. The Lancet 372(9650): 1655-1660.