People taking vitamins and other nutritional supplements may be unaware of "upper intake levels" and as a result consume too much of certain nutrients, according to the results of a new survey conducted in Canada.
Tolerable Upper Levels (ULs) for adults--above which there is increased risk of side effects with regular use-were exceeded for the B vitamin niacin by nearly half of all people who reported taking nutritional supplements, say researchers from McGill University in Quebec.
To investigate the role dietary supplements play in a person's overall nutritional intake, the research team surveyed 1,530 Canadian adults between the ages of 19 and 65. The men and women were asked about the foods they ate and dietary supplements, if any, that they consumed during the 24 hours prior to the interview. The researchers also recorded supplement types, brand names and doses.
Although supplements enhanced dietary intakes of some nutrients, supplements were also shown to have excessive amounts of nutrients in relation to dietary requirements. Specifically, the researchers found excessive intakes of niacin, vitamin A and vitamin B6.
The UL for niacin (35 mg), which in excess can cause flushing and heart palpitations, was exceeded by 47% of nutritive supplement users. Eight women reported taking levels of vitamin A that could lead to liver damage, and could also result in birth defects if they became pregnant (the UL for vitamin A is 3000 micrograms). In addition, 17 people were taking vitamin B6 at levels linked to irreversible neurological damage. The UL for B6 is 100 milligrams per day.
Although not every person exceeding ULs will experience adverse health (ULs are set with a margin of error and at a level to prevent any adverse effect), it is impossible to identify those persons who are at greatest risk.
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