Drinking enough water will ensure that your lips get moisture from the inside out, but sometimes, chapped, dry or cracked lips are actually a result of a vitamin deficiency. All of the B complex vitamins contribute to your skin's health, but some key players, such as niacin (vitamin B3) and riboflavin (vitamin B2) really boost your skin's ability to retain moisture.
Green vegetables such as spinach, Swiss chard, green beans and collard greens are fantastic sources of niacin, and riboflavin is readily available in dairy foods and almonds. For optimal skin (and thus lip) health, you should, of course, eat a balanced diet. But if you sometimes struggle to get all your fruit and vegetable servings each day, it's a good idea to supplement with a multivitamin.