Water-soluble vitamins (such as vitamin C, vitamin B6, vitamin B12, and folate) must be dissolved in water before they can be absorbed by the body and, as a result, cannot be stored. Any water-soluble vitamins that the body does not use are mainly lost through urine. Generally speaking, the body does not store most vitamins, and deficiencies in these vitamins usually appear within weeks or months. Therefore, it is essential for people to consume them regularly. Those who take blood-thinning (anticoagulant) medications may be deficient in vitamin K, but they should not change their vitamin K intake without consulting a doctor.
Vitamin D is beneficial for the body as it plays a role in immunity and controlling cell growth, and may protect against osteoporosis, high blood pressure, cancer and other diseases. People at high risk of vitamin deficiencies (such as those who have had bariatric surgery) should consult their doctor to determine if supplementation is necessary. Vitamin A deficiency in the United States is rare, but the resulting condition is known as xerophthalmia, which can cause blindness if left untreated. It would be difficult to reach this level by eating food alone, but some multivitamin supplements contain high doses of vitamin A. Dietary sources of vitamin D are somewhat limited, but include milk and other fortified dairy products, cod and oily fish (herring, sardines, salmon) and mushrooms. The eight B vitamins that make up the “B complex” are thiamine (vitamin B1), riboflavin (vitamin B2), niacin (vitamin B3), vitamin B6 (pyridoxine), folate (folic acid), vitamin B12, biotin and pantothenic acid).
Although a tolerable upper intake level (UL) has not been established for vitamin K, excessive amounts can cause red blood cells to break down and damage the liver. Signs of vitamin D toxicity include excess calcium in the blood, delayed mental and physical growth, decreased appetite, nausea, and vomiting. Low-fat diets can also cause a deficiency because fats in food help the body absorb fat-soluble vitamins. The effectiveness of vitamin A supplementation for treating measles in countries such as the United States where vitamin A intake is generally adequate is uncertain. Other signs of a possible vitamin A deficiency include decreased resistance to infections, defective tooth development, and slower bone growth.
The best way to get all the vitamins you need every day is to eat a balanced diet that contains a wide variety of fruits, vegetables, fortified dairy products, legumes (dried beans), lentils and whole grains. About 60 percent of dietary vitamin E comes from vegetable oil (soy, corn, cotton and safflower).