Sunscreen prevents sunlight from synthesizing vitamin D, and it's difficult to get this essential nutrient from milk alone, so doctors recommend giving children 400 international units (IUs) of vitamin D daily. (babycenter.com)
Unlike dogs and cats, hamsters can not synthesize Vitamin C on their own, so they have to meet their needs by getting it from their food. (petconsider.com)
Your body synthesizes vitamin A from carotenoids found in dark green, yellow, and orange vegetables like spinach, carrots, and sweet potatoes. (mindbodygreen.com)