Nature's Bounty immune 24 Hour + with ester-C vitamin C provides advanced, long-lasting immune support to help keep you healthy. With 1,000 mg of clinically studied ester-C, it's the only vitamin C that stays in your white blood cells for up to 24 hours, providing immune support around the clock. Highly bioavailable ester-C can increase vitamin C levels in the body, which is important for white blood cell function, as white blood cells play a vital role in the immune system and contribute to the health of the upper respiratory tract. For additional wellness benefits, Nature's Bounty immune 24 hour + rapid release softgels contain Vitamin D, Vitamin A, plus Zinc for extra immune and antioxidant support. In addition, the immune-supporting formula is non-GMO, and free of artificial flavors, artificial sweeteners, sugar, starch, milk, lactose, soy, gluten, wheat, yeast, fish, and sodium. The vitamin C 1000mg supplement also includes herbal ingredients elderberry and echinacea, plus 9 essential nutrients for your overall health.