Excess vitamins are unnecessary for most healthy individuals, as your body only uses what it needs and the rest is either excreted or stored. Absorption or excretion depends on the type of vitamin, possible drug interactions and your dietary needs. Speak with your doctor before taking vitamin supplements or making other dietary changes.
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Vitamins are either water-soluble or fat-soluble. Your body uses water-soluble C and B vitamins quickly and excess amounts are secreted in urine. Excess fat-soluble vitamins A, D, E and K are stored in the liver and fat tissues. While either type may be harmful if taken in large amounts, excessive fat-soluble vitamins are more likely to be toxic due to slower absorption and longer storage.
The Food and Nutrition Board establishes guidelines for daily dietary needs. Commonly used terms in the guidelines include Recommended Dietary Intake (RDA), Dietary Reference Intakes (DRI) and Tolerable Upper Intake Level (UL). Most vitamin supplements and food labels list a Daily Value (DV), illustrating the percentage of a vitamin’s recommended daily amount per serving. The DV percentages are based on adult 2,000-calorie diets. When prescribed by a doctor or dietitian, MayoClinic.com recommends multivitamins containing 100 percent of the Daily Value of all vitamins and minerals and cautions against "megadose" supplements.
According to the Food and Drug Administration, most Americans get all the vitamins they need from foods. However, your physician may recommend supplements for some illnesses, if your diet fails to provide adequate vitamins or if you're pregnant or nursing. Daily vitamin supplements are not a substitute for healthy eating habits and whole foods contain micronutrients and antioxidants not found in supplements.
Speak with your doctor and pharmacist about drug interactions between over-the-counter or prescription medication and vitamins. Laxatives cause foods and supplements to move through the body quickly, resulting in the excretion of many nutrients. Some cholesterol medications reduce bile needed for fat-soluble vitamins, resulting in reduced vitamin absorption. Alternately, vitamin K may reduce the effectiveness of blood thinners.
Symptoms of taking too much of a vitamin varies from headaches and nausea to weight loss and dizziness. However, large amounts of some vitamins are linked to more serious health concerns. Excessive consumption of vitamin A may result in liver toxicity and birth defects. Excessive vitamin C is linked to kidney stones and increased iron absorption. An overdose of vitamin D may cause calcium deposits and irregular heart rhythms.Taking too much vitamin B-6 may cause nerve damage.