Ahead of the World Health Day theme focusing on depression, the World Health Organisation on Thursday said that depression is the leading cause of ill health and disability worldwide.WHO's latest estimates say over 300 million people live with depression, an increase of more than 18% between 2005 and 2015. The new estimates have been released in the lead-up to World Health Day on April 7, the high point in WHO’s year-long campaign 'Depression: let’s talk'. "The overall goal of the campaign is that more people with depression, everywhere in the world, both seek and get help,'' said a press release sent by WHO The release quoted WHO director-general Dr Margaret Chan as saying, “These new figures are a wake-up call for all countries to re-think their approaches to mental health and to treat it with the urgency that it deserves.”Last year, the Bengaluru-based National Institute of Mental health & Neuro Sciences (NIMHANS) carried out a survey and said that one out of 20 Indians suffers from depression at some point in their life.The WHO has called for increased investment in mental health infrastructure. ``In many countries, there is no, or very little, support available for people with mental health disorders. Even in high-income countries, nearly 50% of people with depression do not get treatment. On average, just 3% of government health budgets is invested in mental health, varying from less than 1% in low-income countries to 5% in high-income countries,'' said WHO officials. They added that every US$ 1 invested in scaling up treatment for depression and anxiety leads to a return of US$ 4 in better health and ability to work.