Popping a daily multivitamin pill could be a waste of time and money, says consumer watchdog Choice.
Healthy individuals who already eat a balanced diet but also take multivitamins could be spending money unnecessarily, an investigation by Choice found.
Although there is sometimes clinical evidence to support taking a supplement, the doses can often be way below levels required to have a significant impact, the organisation said.
"If you have a healthy diet and you're not a person with specific nutritional requirements, there's a good chance you're wasting your money," Choice spokeswoman Ingrid Just said.
"At 20 to 70 cents per day for multivitamin products we priced, the 'worried well' can spend several-hundred dollars a year simply by taking a daily pill.
"Marketing messages, often backed up by high-profile sporting celebrities, give the impression that we all need multivitamins to be fit and healthy."
People taking a range of multivitamins without checking the recommended daily intake (RDI) requirements could be exceeding the RDI for some vitamins and potentially putting their health at risk, because not all vitamins are safe in high doses.
But most multivitamins contain lower doses of ingredients so it's harder for them to be overconsumed, the investigation found.
Vitamin labelling could also confuse consumers, with some labels stating the vitamin name such as B3, while others using the chemical name, niacin.
"An untrained person probably wouldn't know that the two things are one and the same," Ms Just said.
Manufacturers of products sold in Australia are not required to list how each ingredient amount relates to RDI.
"We want manufacturers to list vitamin and mineral values according to the percentage of an appropriate RDI in each dose to help consumers compare apples with apples," Choice's investigation found.
Multivitamins are big business, with Choice identifying eight multivitamin products marketed by both Blackmores and Nature's Own, 11 by Nature's Way and 16 by Swisse.
But some groups definitely benefit from supplements, including pregnant women taking folate before and after conception, the study pointed out.
Choice recommends individuals consult a dietician or GP about their nutritional needs before opting for multivitamin or other supplements.
SUPPLEMENTS: WHO NEEDS THEM?
* FOLATE: Pregnant women and those trying to conceive.
* VITAMIN D: People with limited exposure to sunlight such as institutionalised or bedbound elderly, dark-skinned people and veiled women.
* VITAMIN B12: People on a strict vegan diet and the frail aged who may be eating poorly and/or absorbing less from their food.
* OTHERS: People on restrictive diets (including those with eating disorders, food allergies or intolerances and those on low-kilojoule weight-loss diets). Supplement depends on the diet.