India's Prime Minister Narendra Modi has asked world leaders to start U.N. International Yoga Day. He was speaking at U.N. General Assembly in New York. It was his very first speech at 193-member General Assembly. He spoke about benefits of yoga, saying it was good for mind and body, and could also help climate change. He said yoga provides harmony between humans and nature, and is " invaluable gift" from India's 5,000-year-old culture. Modi said: "It is not about exercise, but to discover sense of oneness with yourself, world and nature." He added: "By changing our lifestyle and creating consciousness, it can help us deal with climate change." Many doctors and people in medical community say yoga is good way to stay physically and mentally healthy. Yoga makes you focus on exercise, breathing and meditation. lot of research says it can help people with heart disease, high blood pressure and lower back pain. Studies also say yoga can improve our mood, reduce stress and make us sleep better. However, there is also research that says people need to be careful when doing yoga. Wikipedia says: " extensive survey of yoga practitioners in Australia showed that about 20 per cent had suffered some physical injury while practicing yoga." World Yoga Day already exists. It was started by world-yoga-day.org website in 2007.