Dietary supplements vs food: What’s really the best way to get nutrients?

Question:

I try to make my diet as nutrient-dense as possible every day. I’m bombarded with information about the goodness of so many foods, and I’m anxious to include them all. But how much is too much?

Answer:

The excessive consumption of certain vitamins and minerals can have unintended adverse effects on the health of children and adults. But where exactly is the line between a healthy, nutritious diet and one that contains excessive nutrients that could cause harm? The answer has a lot to do with the source of the nutrients: dietary supplements versus food.

National health organisations worldwide have put considerable research into determining the optimal nutrient intake to guide the general population. For most, but not all, nutrients, there is a threshold between intake levels that are known to be safe and those that are potentially unsafe – the boundary between the two is called the “upper limit of nutrient intake”.

For instance, the World Health Organisation’s food and agriculture agency defines the upper tolerable nutrient intake levels (ULs) as the maximum amount of chronic intake “unlikely to pose a risk of adverse health effects from excess in almost all (97.5 per cent) apparently healthy individuals in an age- and sex-specific population group”.

Nutrient intakes at or near the UL can be tolerated by most people over the long term. But as your intake rises above the defined UL, there is a greater likelihood of adverse effects. And the longer your intake stays above the limit, the greater the risk of harm. So, yes, you can have too much of a good thing.

However, it is rare for people to exceed the UL for nutrients from food alone. Indeed, for most nutrients required by our body, there are no anticipated adverse effects when consumed as foods because our metabolism will sort out the details by altering absorption and excretion to regulate our balance of those critical nutrients.

Instead, excessive intake of nutrients is more likely to occur when people add high-dose micronutrient supplements to their diet. An observational study published in the Annals of Internal Medicine in 2019 assessed the dietary habits and supplement use of nearly 31,000 American adults. It found evidence that adequate intake of some nutrients (eg, vitamin A and K, magnesium and zinc) were associated with increased lifespan, but only when people sourced those nutrients from food. In contrast, it concluded that excessive intake of some nutrients from dietary supplements may have an adverse effect on mortality risk.