Health Options
Nutrient excess
causes reactionsLast week's "Health Options" column explored how much is too much for some key vitamins and minerals. This week, we describe some of the potential negative effects that can occur from intake that exceeds the "Tolerable Upper Intake Levels" (ULs) established by the Institute of Medicine.
Question: Will consuming a nutrient at the UL level always lead to side effects?
Answer: No. UL values are typically set below the lowest amount of a nutrient that is known to cause side effects. Most people will not experience any obvious effects at those levels.
Q: If a person exceeds the Upper Limit for a nutrient, how soon do the negative effects appear?
A: Depending on the nutrient, negative effects can occur within minutes or take years. For example, excessive niacin can create flushing and tingling sensations within minutes of a high dose.
A quite noticeable and likely embarrassing reaction occurs within a few hours of consuming excess supplemental magnesium. The upper limit is set at 350 mg of non-dietary magnesium per day, because much more than this causes very loose stools and in some people, explosive diarrhea.
Other micronutrients that can cause gastrointestinal problems in excess amounts are vitamin C, niacin, calcium, copper and iron.
Q: For micronutrients that do not have immediate negative effects, will a person know if they are accumulating dangerous levels?
A: Not usually. For example, niacin, even at doses that do not cause flushing, may bring about liver damage that is not initially noticeable. For this reason, when physicians prescribe niacin to reduce high blood-cholesterol levels, they periodically run blood tests to make sure that the liver is not being damaged.
Exceeding the UL for vitamin A during pregnancy greatly increases the risk of serious birth defects in the developing infant. However, because vitamin A is essential for normal development, the Food and Drug Administration recommends that during childbearing years, women consume vitamin A at the RDA level. Eating those fruits and vegetables becomes more important than ever during pregnancy.
But excess vitamin A, taken over a length of time, can be harmful to children and non-pregnant individuals, causing liver damage and a host of other problems.
Vitamin B6 taken in excess (greater than 100 mg per day) can damage nerves that serve the arms, legs, hands and feet. The effects can be permanent.
Prescription drugs are known to have many side effects. And excesses of many nutrients have very similar side effects. Therefore, it is especially important to know the side effects of the upper-limit nutrients you may be taking.
Nutrient damage
These are examples of the negative side effects possible from excess intake of various nutrients:
Nutrient Side effects Vitamin A Birth defects, liver damage Vitamin C Intestinal distress, kidney stones Vitamin D Kidney damage Vitamin E Poor blood clotting Niacin Flushing, liver damage Vitamin B-6 Nerve damage Calcium Kidney problems Magnesium Diarrhea Iron Intestinal distress Selenium Hair loss, brittle nails Copper Intestinal distress, liver damage Manganese Nerve toxicity Health Events
Alan Titchenal, Ph.D., C.N.S., is a sports nutritionist in the
Department of Human Nutrition, Food and Animal Science,
University of Hawaii-Manoa.Joannie Dobbs, Ph.D., C.N.S., is a food and nutrition consultant
and owner of Exploring New Concepts, a nutritional consulting firm.
She is also responsible for the nutritional analyses
indicated by an asterisk in this section.