Why your daily multivitamin won’t help you live longer

Over 8.2 million Australians buy some form of vitamin, supplement or mineral every six months, in what is estimated to be a five billion-dollar industry. But how much are they doing for our health?

A new study, released on Thursday in the US, found that multivitamins do not increase longevity.

Multivitamins have not been shown to increase longevity.

What does the study say?

Published in JAMA, researchers surveyed almost 400,000 generally healthy US adults over two decades. They concluded that “people who take daily multivitamins are no less likely to die from any cause than those who don’t.”

Interestingly, they also found people who take a daily multivitamin were associated with a four per cent higher mortality risk, but this could be because those with existing health conditions are more likely to take a supplement.

The findings add to existing research that shows multivitamins do little to make those without vitamin deficiencies healthier.

‘A lot of people who are undergoing treatment for cancer … will take multivitamins. And of course, they’re at a much higher risk of death.’

Dr Nial Wheate from Macquarie University

Dr Nial Wheate, a professor and Director of Academic Excellence at Macquarie University, is not surprised by the results. “This confirms what we’ve thought for a long time: that a lot of people who are taking multivitamins are doing so without a need to do it.”

Wheate echoes a sentiment expressed by the authors of the study on potential positive or negative associations with multivitamin use, saying those who take supplements are either more likely to be health conscious in other areas of their lives or are taking them as a form of disease management.

“One of the blind spots is that quite a few people who are taking multivitamins are not doing it for conditions or diseases associated with mortality. A lot of people are doing it to improve overall health or for short-term things like the flu, which of course would not result in reduced mortality in the long run.”

On the other hand, “a lot of people who are undergoing treatment for cancer will do everything they can to try and improve their chances. And a lot of them will take multivitamins. And of course, they’re at a much higher risk of death.”

Who needs a multivitamin?

Professor Lauren Ball, Chair of Community Health and Wellbeing at The University of Queensland, says most people do not need to take a multivitamin as long as they’re eating a balanced diet.

“Unless someone is really unable to consume foods, older adults for example because of mouth issues, or young children who are fussy eaters, they’re not going to do much. They’re really the only situations when I would think that a general multivitamin would be advised because the vitamins in tablets are so abundant in our food supply.”

She says pregnant people are advised to take a multivitamin, as well as those trying to conceive.

Are there any benefits besides longevity?

Modest studies have shown an association between multivitamin use and things not linked to longevity, like improved cognition.

Despite this, Wheate is sceptical. “It’s important to remember that a lot of multivitamins, despite their claims, haven’t been tested to actually show they’re efficacious for the conditions that they’re talking about. Most multivitamins in Australia are listed medicines, which means they’ve only been proven to be safe but not necessarily effective.”

He adds that it’s important to consider cause and effect when looking at these studies.

“A lot of people who take vitamins to improve their health are also the same types of people who are doing other things to improve their health. And if they have better brain cognition or tend to live longer, it could be because of other factors that aren’t to do with the vitamins.”

Ultimately, Wheate says the only people who would benefit from a multivitamin are those who have been shown to be nutrient-deficient, particularly those with restricted diets like vegetarians or vegans.

What are the risks?

Ball says the risks associated with taking vitamins are low. In most cases, she says our body will simply excrete the excess nutrients, since most vitamins and minerals are water-soluble.

When it comes to vitamins that are not water-soluble, like vitamins A, D, E and K, there is a small risk for certain segments of the population. High levels of vitamin A, for instance, can be harmful for infants. And too much vitamin K, she says, can be problematic for those with certain blood clotting illnesses.

“But we’re talking really small parts of the population, and they’re in really low doses in multivitamins anyway, so it’s a pretty low risk,” she says.

Wheate says it is possible to overdose on a vitamin, but “what’s more concerning is vitamins have the ability to have drug interactions with regular medicines, which means they could reduce the effectiveness of medicines or increase the side effects of those medicines.”

He says it’s always important to consult with a doctor or pharmacist if you’re taking a multivitamin while on other medications.

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Key points

Over 8.2 million Australians buy some form of vitamin, supplement or mineral.

Existing research shows multivitamins do little to make those without vitamin deficiencies healthier.

Experts emphasise the importance of nutrition and a balanced diet for longevity.