Supplements are no cottage industry: an estimated third to nearly half of Australians regularly take vitamins or minerals.

Hawked by the likes of the Kardashian-Jenner clan, vitamin gummies have in recent years found popularity among millennials and zoomers, who are more receptive to supplements in the form of “powders, liquids and gummies” than older generations. Gwyneth Paltrow’s Goop – no stranger to dubious health trends – sells its own line of such supplements.

On TikTok, influencers who shill multivitamin gummies – and more recently, vitamin patches resembling cutesy, colourful stickers or fine line tattoos – promise glowing skin, lush locks, energy boosts and better sleep. But if it’s real health benefits you’re after, you’re better off saving your pennies.

What does the evidence say about multivitamins?

The average person can get their recommended intake of vitamins (which have a plant or animal origin, such as vitamin C and vitamin B12) and minerals (elements such as iron, zinc and iodine) from food alone.

“A person who is healthy and has access to a balanced diet, particularly whole foods, generally does not need vitamin supplements,” says Barbara Mintzes, professor of evidence-based pharmaceutical policy at the University of Sydney.

“In almost all cases, people are paying a lot of money for things that are not providing them any benefit at all,” agrees Prof Nial Wheate, director of academic excellence and a medicines researcher at Macquarie University.

Multivitamins contain a variety of vitamins and minerals – experts often quip that they make for very expensive urine. “A lot of vitamins are water soluble. So once you’ve saturated your body stores, you just wee them out,” says Clare Collins, a professor of nutrition and dietetics at the University of Newcastle.

While specific supplements are important for conditions linked to nutrient deficiencies (more on this later), for the general population there is scant evidence multivitamins have any health benefits.

Numerous meta-analyses – which analyse results from multiple studies – have found multivitamins do not improve heart health, reduce the risk of certain cancers or make people live longer. An Australian meta-analysis of trials in older adults found multivitamins made no difference to mortality risk.

Collins suspects multivitamins are so popular because they are taken as an insurance policy of sorts. “I think it’s because people know they probably don’t eat as healthily as they should.

“Unfortunately, you’re not necessarily getting everything you need [from multivitamins] like dietary fibres and other items … such as phytonutrients, plant-based chemicals that occur naturally in a range of foods.”

In some cases, supplements can do more harm than good. Some fat-soluble vitamins, such as vitamin A, are stored in the liver and can accumulate to dangerous levels if overconsumed, though Collins says this is unlikely to occur from multivitamins. “Harm tends to come when [people] isolate out just one and take megadoses of that.”

For supplements that purport to have specific benefits – such as hair, skin and nail formulations – Dr Helen Macpherson, a senior research fellow at Deakin University’s Institute for Physical Activity and Nutrition, advises wariness about health claims being made. “Often the ingredients are [in concentrations] just too low to have any physiological benefit,” she says.

Vitamins marketed specifically for hair, skin and nail health often contain biotin, a B vitamin that one review found had “no proven efficacy in hair and nail growth of healthy individuals”. A US study of 176 products marketed as hair, skin and nail supplements found they contained 255 distinct ingredients, including biotin at doses ranging between 100% and 33,333% of the recommended daily intake. US regulators have repeatedly issued warnings that biotin can interfere with lab tests, giving false results for troponin, a biomarker used to diagnose heart attacks.

In Australia, most multivitamins are regulated by the Therapeutic Goods Administration as “listed” medicines, which have less stringent rules than those classified as “registered” medicines, such as prescription drugs. “When someone starts a vitamin company, the only thing they have to prove to the government is that it’s safe. They do not have to prove that it works,” Wheate says.

According to Wheate, vitamin patches contain very low concentrations of ingredients, and there’s no guarantee they even work because not all drugs can be delivered through the skin. There are no vitamin patches currently listed on the Australian Register of Therapeutic Goods, meaning they cannot be legally supplied in Australia.

And what of gummies sold by Kourtney Kardashian, which supposedly support “vaginal health, freshness and odour”? They “do not add any health benefits for women”, one expert found in a thorough but civil rubbishing.

Who are vitamin supplements good for?

In certain cases, there are clear benefits to taking supplements. Vegans, for example, are at higher risk of vitamin B12 deficiency, because it is the only vitamin that humans get exclusively from animal sources – though Collins says it is often added to plant-based milk products.

Iron supplements may be required to prevent or treat iron-deficiency anaemia. Likewise, people at higher risk of osteoporosis, such as postmenopausal women, may be advised to take calcium and vitamin D to supplement dietary intake.

Folate, iodine and vitamin D supplements are recommended for pregnant women because they are required for a foetus to develop normally. Vitamin D supplements may also be required for people with darker skin or who don’t get much sun.

And for people with age-related macular degeneration, a combination of zinc and antioxidants known as AREDS2 supplements can reduce the risk of the condition worsening.

“Absolutely there is a place for taking vitamin supplements,” says Macpherson. “Individuals really need to work with their healthcare provider to address those [nutrient deficiencies]. Taking a multivitamin in those cases isn’t going to be sufficient anyway.”

• Donna Lu is Guardian Australia’s science writer

• Antiviral is a fortnightly column that interrogates the evidence behind the health headlines and factchecks popular wellness claims.