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“One blind spot is that many people who take multivitamins aren’t taking them for any symptoms or illnesses that are associated with mortality. Many take them to improve their overall health or for short-term symptoms like the flu, which of course doesn’t translate to reduced mortality in the long term.”
Meanwhile, “many people undergoing cancer treatment will do anything to improve their chances of survival, and many of them will take multivitamins. And, of course, they’re at much higher risk of dying.”
Who needs a multivitamin?
Professor Lauren Ball, director of community health and wellbeing at the University of Queensland, said most people didn’t need to take a multivitamin if they had a balanced diet.
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“Multivitamins don’t do much good unless you’re someone who really can’t consume food, like older people with oral issues or picky young children. Because vitamins in pill form are so abundant in our food supply, I think that’s the only situation in which a general multivitamin would be recommended.”
She says that not only those who are trying to conceive, but also those who are pregnant, are advised to take a multivitamin.
Are there any benefits other than longevity?
Modest studies have shown a link between multivitamin use and things unrelated to longevity, like improved cognitive performance.
Despite this, Wheat is sceptical: “It’s important to remember that many multivitamins, despite their claims, have not actually been tested to see if they work for any condition. Most multivitamins in Australia are registered medicines, which means they are only proven to be safe, not necessarily effective.”
He added that it’s important to consider causation when looking at these studies.
“Many people who take vitamins to improve their health are also doing other things to improve their health, and if they have better cognitive function or live longer, it may be due to other factors that have nothing to do with vitamins.”
Ultimately, the only people who benefit from a multivitamin are those with known nutritional deficiencies, especially those on restrictive diets like vegetarians and vegans, Wheat says.
What are the risks?
Ball says the risks associated with taking vitamins are low: Most vitamins and minerals are water-soluble, so in most cases, the body just flushes out the excess nutrients, he says.
There are small risks for certain populations when it comes to vitamins that aren’t water-soluble, such as A, D, E and K. Too much vitamin A, for example, can be harmful to infants, and too much vitamin K can be problematic for people with certain blood-clotting disorders, she says.
“But we’re talking about a very small percentage of the population, and they have very low levels of multivitamin intake, so the risk is quite low,” she says.
Wheat says that while it’s possible to take too many vitamins, “a bigger concern is that vitamins can interact with common medications — making them less effective or increasing their side effects.”
He says it’s important to always check with your doctor or pharmacist if you’re taking a multivitamin while also taking other medications.
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