Some multivitamins provide only a fraction of the full range of vitamins and minerals needed, and at levels that may be well below the recommended doses – so they may provide very little benefit.
Over-consumption of certain vitamins or minerals can be dangerous. But with a multivitamin, ingredients are generally present at a lower dose than in individual supplements so it’s harder for them to be over-consumed and cause damage.
“There’s only so much of each nutrient you can pack into a multivitamin pill – in that way they’re self-limiting – and often it’s not even close to the RDI,” says Crowe. “Taken as directed there’s little chance of harm as a dose is unlikely to contain levels of nutrients above the recommended upper level of intake.”
The downside of this is that some multivitamins provide only a fraction of the full range of vitamins and minerals needed, and at levels that may be well below the recommended doses – so they may provide very little benefit. The cost of some popular multivitamins that we priced ranged from 20-70c per day. When taken daily over weeks, months and years, this can really add up.
To complicate matters, it’s very difficult for a lay-person to know what they’re getting in a multivitamin and compare products.
- Names Vitamins are listed under their vitamin name on some bottles (e.g. vitamin B3) and their chemical name (e.g. niacin) on others. Different brands produce the same basic supplement from different compounds, any of which may appear on the bottle. For instance, calcium can be derived from calcium phosphate, calcium pantothenate, calcium ascorbate, calcium carbonate or calcium orotate (amongst others).
- Quantities With quantities, some companies list the weight of the ingredient (which could be a compound), while others state the vitamin or mineral equivalent of that ingredient. And manufacturers of products sold in Australia don’t need to list how much of each ingredient relates to an RDI.
Too much of a good thing
According to Dr Trent Watson, “the law of toxicology suggests that anything in the right doses can be toxic. There’s an increasing body of evidence that suggests large doses of vitamin A increases the risk of lung cancer, for example.”
There are situations when multivitamins might not always be safe. There’s some evidence that high levels of iron supplements prescribed to pregnant and lactating women may decrease zinc absorption. “A leading cause of poisoning in children is iron poisoning,” says Tim Crowe.
“While the quantity in one multivitamin tablet is perfectly safe, if a kid thinks they’re lollies and eats the whole packet then there’s the potential for harm.”
If you're taking vitamin or mineral supplements or natural or herbal remedies along with prescribed medicine, it's important to be aware of possible interactive effects.