The vitamin boom: Do supplements really work?

Nowhere are New Zealanders’ conflicted attitudes to vitamin supplements better illustrated than in the Dunedin home of Dr Lisa Houghton, a professor of nutrition at the University of Otago, and her accountant husband Brett Dailey.

Ask Houghton whether it's a good idea to take multivitamins and she'll tell you the people who need them least are those who take them most; that we get the critical nutrients we need from our food. Apart from taking iron when she was younger, she doesn't use them. Then she laughs and adds, "But my husband loves them." Dailey, she says, has given each of their three daughters, now in their teens and early twenties, a multivitamin tablet each day since they were preschoolers.

All five have been vegetarians for several years and oldest daughter Erin is trying veganism, but Houghton, who does most of the cooking, ensures they get healthy, balanced meals. But Dailey says even before they moved to a plant-based diet, he offered multivitamins as a kind of dietary insurance policy. "From a young age, they had the chewable tablets and we just kept up with it the whole time. I always felt diet can't be perfect every day, that's for sure." He says Houghton "doesn't tell me not to do it, but sometimes she rolls her eyes at the supermarket when I'm buying them. I'm just trying to fill a gap." He says although healthy meals are always available, the girls "don't always eat everything they should".

Dailey accepts that his attitudes are based more on his heart than his head, but he’s not alone. In New Zealand, research by market analysts IRI shows the vitamin and supplements market is worth $473 million a year – up 65 per cent on 2015 – with multivitamins the largest sector at about $40 million. Research in the US suggests supplement users are typically older, healthier, wealthier and Caucasian – a demographic that’s unlikely to be very different here. “It still stands that the people who take them the most need them the least,” says Houghton.

Sales increased further during Covid. In the six months to August 2020, sales of vitamins in the “cold and flu” category rose 8.9 per cent, when compared with the same period the year before, and sales of cold and flu products suggesting they could boost immunity were up nearly 6 per cent. And that’s with zero evidence that over-the-counter medicines make any difference.

Despite that, and the staggering cumulative cost, we rationalise that if they won’t hurt us, only our pocket, what’s wrong with a top-up just in case we go off the dietary rails from time to time. In December 2018, New Scientist magazine identified three groups for whom some supplements may be useful: women who are pregnant or trying to conceive should consider taking folic acid , which has been estimated to more than halve the risk of neural tube defects such as spina bifida; infants who are exclusively or partially breastfed may benefit from supplemental vitamin D, which is present at very low levels in breast milk; and adults over the age of 50 who may absorb less of certain nutrients, including vitamin D, because they produce less stomach acid.

Vitamin D and calcium supplements can increase bone strength and calcium supplements can reduce the risk of fractures. It’s also common practice for vegans to require supplementation with vitamin B12, which is not found in plants, although nut milks are often fortified.

Houghton says although physiological changes as we age can increase the need for some supplements, "Mother Nature does a lovely job of making sure we don't need as much as we used to of some things, including iron".

But at the University of Canterbury’s School of Psychology, Speech and Hearing, researcher Professor Julia Rucklidge is frustrated our laws mean that even when there is evidence that some supplements – such as a micronutrient combination she uses in her clinical trials – have a therapeutic effect, they can’t be sold in sufficient strength because they would then be categorised as medicines, which would require them to be regulated under the Medicines Act. It’s the reason dietary-supplement manufacturers are deliberately vague when they promote their products and avoid therapeutic claims, mostly resorting to the nebulous suggestion of “supporting” or “promoting” a bodily function such as sleep, joint, brain or digestive health. At present, dietary supplements are regulated as “foods”, so are not tested for efficacy or toxicity.