Exposure to sunlight for about 15 to 30 minutes, two to three times a week, is adequate for most individuals to maintain sufficient vitamin D levels. If that seems punishing in hot weather, stay hydrated. The body can make all the vitamin D it needs for a day in about half the time it takes the skin to burn, says Dr Tarun Sahani, Senior Consultant, Internal Medicine, Indraprastha Apollo Hospitals, New Delhi