Nutrient supplements do no good, may do harm


Vitamins from food and pills have different effects, study finds. Samantha Page reports.


At best, a waste of money. Diet supplements are implicated in mortality risk.

Blend Images - Tanya Constantine/Getty Images

The only vitamins that help are the ones you get from food, a new study suggests.

Researchers at Tufts University in the US find that vitamin and mineral supplements are at best a waste of money, and at worst are correlated with increased mortality rates.

The study, led by nutrition specialist Fang Fang Zhang and published in the journal Annals of Internal Medicine, finds that adequate intakes of vitamin K and magnesium are associated with lower all-cause mortality rates, but the findings hold true only for intake from food sources, not from vitamin supplements.

On the other hand, excess calcium intake, including from supplements, was linked to a higher rate of cancer mortality.

Vitamin D supplement intake for individuals with no vitamin D deficiency was linked to higher all-cause mortality rates.

“As potential benefits and harms of supplement use continue to be studied, some studies have found associations between excess nutrient intake and adverse outcomes, including increased risk of certain cancers,” Zhang says.

“It is important to understand the role that the nutrient and its source might play in health outcomes, particularly if the effect might not be beneficial.”

The study is based on data from 27,725 adults who had answered a range of health and nutrition questions and completed at least one 24-hour food log for the US National Health and Nutrition Examination Survey between 2006 and 2011.

More than half of the participants had used at least one dietary supplement within the previous 30 days, with over 38% using a multivitamin or mineral product.

Supplement users were more likely than the rest of the population to get nutrients through their food. They were also disproportionately older, wealthier, whiter, more educated, physically active, and female.

They were less likely to smoke, drink heavily, or be obese. In other words, they were people with the resources and inclination to take care of their bodies.

"Our results support the idea that, while supplement use contributes to an increased level of total nutrient intake, there are beneficial associations with nutrients from foods that aren't seen with supplements," said Zhang.

"This study also confirms the importance of identifying the nutrient source when evaluating mortality outcomes."

  1. http://dx.doi.org/10.7326/M18-2478
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