New York, Feb 24 : Depression is the leading cause of disability worldwide, the United Nations health agency on Thursday reported, estimating that it affects more than 300 million people worldwide – the majority of them women, young people and the elderly. An estimated 4.4 per cent of the global population suffers from depression, according to a report released on Thursday by the UN World Health Organization , which shows an 18 per cent increase in the number of people living with depression between 2005 and 2015.