There are many individuals with vitamin D deficiency, especially those that follow a strict vegetarian diet, do not get enough exposure to the sun, or suffer from milk allergies. Symptoms of vitamin D deficiency include muscle weakness, diabetes, chronic kidney disease, psoriasis, cardiovascular disease, asthma, periodontal disease, depression, and schizophrenia. It is extremely important to make sure you get enough vitamin D every day. Numerous foods contain sufficient amounts of vitamin D including cod liver oil, swordfish, salmon, tuna fish, orange juice fortified with vitamin D, milk, margarine, liver, eggs, Swiss cheese, and ready-to-eat cereal. Sun exposure also helps you absorb vitamin D through your skin. Another way to make sure you get enough vitamin D3 is by taking a dietary supplement, such as Liquid Vitamin D3. This supplement contains 1,000 IU in just one drop, which is 250 percent daily value. Similar products to Liquid Vitamin D3 include Vitamin K2 with D3, Kid-D Liquid Drops, and Vitamin D 1,000 IU.