Dietary supplements: how to avoid dangerous doses

Overdosing on dietary supplements can be incredibly unsafe. Here's what you need to know about dietary supplements and the dangers of overuse.

• The U.S. National Academy of Sciences and Health Canada have set Tolerable Upper Intake Levels (ULs) for many nutrients, including calcium (2,500 migrograms/day) and vitamin D (2,000 IU/day).
• The UL is defined as the highest level of daily nutrient that is likely to pose no risk or adverse health effects for almost all individuals in the general population. As intake increases above the UL, the potential risk of adverse effects increase.
• Work continues in this area and tolerable upper limits will be identified for more nutrients in the future. In the meantime, common sense should prevail whether or not a tolerable upper limit has been set for a nutrient.

• High doses of vitamin A can cause liver damage, skin problems, fatigue and other symptoms. Taken before and during pregnancy, it can cause serious birth defects.
• High doses of vitamin D can result in calcium deposits in the heart and blood vessels, upset calcium metabolism and lead to bone loss. Taken over an extended period, very large amounts of both vitamins can be fatal.
• Excessive zinc and several trace minerals have effects ranging from nausea and diarrhea to death if taken in doses that allow build-up in body tissues.

• Drugs and nutrients share the same route of absorption and metabolism in our bodies, which creates the potential for interacitons. For example, calcium can bind to certain antibiotics, interfering with their absorption.
• So if you are taking, or plan on taking, therapeutic doses of nutrients in supplement form, be sure to check for the possibility of these types of interactions.

Caution: Smokers who take high-dose beta-carotene supplements actually increase their chances of developing lung cancer, say the results of two large medical trials.

• Ongoing studies continue to stress that everyone should get beneficial antioxidants the old-fashioned way — by eating their fruits and vegetables.