What Is a Vitamin Megadose?
Although there is no clear-cut explanation of what exactly constitutes a vitamin megadose, according to Harvard University Medical School, it is generally a vitamin intake many times higher than the recommended amount. You can safely take some nutrients in high amounts, but do not exceed the IOM's guidelines, as taking too much of some nutrients can cause toxicity and health problems.
Water Soluble vs. Fat Soluble
Taking megadoses of water-soluble vitamins is generally safer than megadosing on fat-soluble vitamins. When you take in large amounts of water-soluble vitamins, your body uses what it needs and sends the rest to your kidneys, which purge it from your body. When you take in megadoses of fat-soluble vitamins, your body uses some of it and stores the rest for future use. In time, you may be storing toxic levels of these vitamins, putting you at risk for associated health problems.
Tolerable Upper-Intake Levels
To help the public avoid taking toxic megadoses of nutritional products, the Institute of Medicine has established tolerable upper intake levels, or ULs, determining the highest intake level that is likely to pose no adverse health effects to the general population. Although the IOM recommends that men and women, respectively, get 90 and 12 micrograms of vitamin K, 1.1 and 1.2 milligrams of thiamine, 1.1 and 1.3 milligrams of riboflavin, 2.4 micrograms of vitamin B-12, 5 milligrams of pantothenic acid and 30 micrograms of biotin daily, due to a lack of reliable data, it has not published ULs for any of these nutrients.
You need 60 milligrams of vitamin C per day if you are a woman, while men need 75. Because vitamin C is water-soluble and helps your immune system, many people think it is safe and beneficial to take in megadoses. Manufacturers of nutritional supplements add exorbitant amounts of this antioxidant to their products, but the IOM advises that you do not exceed 2,000 milligrams of vitamin C per day. Exceeding this amount can cause diarrhea and kidney stones, according to the McKinley Health Center.
Who May Benefit
Most people can get the nutrients they need from food and moderate nutritional supplementation, according to Colorado State University, but some may need more of certain vitamins. Megadosing beyond the recommended daily intake is usually safe as long as you do not exceed a nutrient's tolerable upper intake level. Older adults may benefit from taking more calcium than the recommended 1,200 milligrams per day and by exceeding their daily recommendations of vitamins B-12 and 20 micrograms of vitamin D. Iron supplementation can be beneficial for young women, who need 18 milligrams of iron a day. Vegans may need extra calcium and B-12 and could benefit from taking supplements that provide more than their recommended 8 to 18 milligrams of iron and 8 to 11 milligrams of zinc.
Maia Appleby is a NASM-certified personal trainer with more than 15 years of experience in the fitness industry. Her articles have been published in a wide variety of print magazines and online publications, including the Gale Encyclopedia of Nursing and Allied Health, New Moon Network and Bodybuilding.com.