What’s actually inside your multivitamin?

A 2017 study published in The American Journal of Clinical Nutrition analysed adult multivitamin/mineral supplements sold in the US to compare their actual nutrient content with their labels.

Researchers found that, for 12 of the 18 nutrients studied, most products contained amounts at or above recommended dietary allowances. The actual measured amount of most ingredients was also higher than the amount listed on the label.

For some nutrients, the difference was relatively small. But the measured amounts of selenium and iodine were, on average, around 25% higher than their labelled amounts.

The study also found that multivitamins can already contain significant amounts of some nutrients. If people take them alongside a regular diet and other supplements, they may end up consuming more than they need.

The researchers did not say that multivitamins could harm a person. Instead, the findings show why it is important to look at a person’s total vitamin and mineral intake — from food and all their supplements — rather than considering each product separately.

When wellness becomes too much of a good thing

The danger with supplements often begins with a seemingly harmless assumption: if a little is good for you, more must be better.

But the body does not necessarily work that way. A vitamin or mineral that is essential in the right amount can become harmful when taken unnecessarily or in excessive doses.

As Dr. Giovanni Leonetti, General Surgeon at Cornerstone Clinic explains, taking supplements blindly without a confirmed biological need poses severe health risks, including organ damage, dangerous prescription drug interactions, and hidden toxicities. “As the body already gets most required nutrients from a balanced diet, adding unneeded concentrated doses often forces organs to work under extreme stress to filter out the excess,” he says.

The effects of taking too much, can push the organs responsible for processing and filtering excess nutrients. Jamie Richards, Valeo Health Chief Wellbeing Officer and Clinical Psychoneuroimmunologist, notes the potential impact on the liver, kidneys, nervous system and digestive tract.

The problem with taking several supplements at once

The morning routine can quickly become a small pharmacy of its own: A multivitamin with breakfast, a beauty supplement for hair and nails, an immunity booster during flu season, and perhaps a separate vitamin D or iron tablet.

As each product is sold for a different purpose, it is easy to assume they are all adding something different to the body. But the labels may tell another story.

The same vitamins and minerals can appear across multiple products, sometimes under different names. In other words, people can unknowingly take overlapping ingredients throughout the day.

This, can culminate in an accidental toxic overdose from cumulative doses and impaired nutrient absorption caused by chemical competition in the digestive tract. As many products, like multivitamins, immune boosters, and hair, nail blends, hide the same vitamins and minerals under different names, ‘supplement stacking’ often pushes intake past safe daily limits,” says Leonetti.

The consequences may not always be immediately obvious. Instead, the body may begin sending out symptoms that can easily be blamed on stress, poor sleep or an entirely different health issue.

It can cause symptoms such as:

The supplements people may be taking unnecessarily

Here are some of the supplements they say deserve particular caution:

1. Iron

Iron is often associated with fatigue, which can make it tempting for people to start taking it after a quick Google search. But supplementation without confirming a deficiency can cause problems.

As Leonetti explains, “For example, magnesium can cause diarrhea at doses above 400 mg/d; phosphorus can cause diarrhea at doses above 750 mg/d, and mild nausea and vomiting at lower doses, and iron can cause constipation, nausea and vomiting.”

Leonetti also warns that high doses of iron can be toxic for individuals with liver disease or hemochromatosis.

2. Vitamin A

Vitamin A is essential, but excessive intake can create toxicity risks.

“Iron, vitamin A, and vitamin B6 all make my list, iron and vitamin A for the toxicity risks already covered, and B6 for the nerve-related symptoms that can come with high usage over time,” says Richards.

3. Calcium

Calcium is perhaps the most surprising supplement on Richards’ list. It is strongly associated with bone health, which can make it tempting to assume that taking more must offer greater protection.

Richards says the issue is not simply whether someone is consuming enough calcium, but also how effectively the body can process and use it.

“Calcium is indeed a very vital nutrient for a host of health reasons, not least for your bones and teeth. However, true calcium deficiency is very rare. What is way more common is a reduced ability to metabolise calcium, for your body to process and use it efficiently.”

He argues that the focus on calcium intake can sometimes overlook the factors that affect how the mineral is absorbed. “Somewhere along the way the message was confused. People with bone issues were given increasingly higher amount of calcium, the very thing we already had enough of but couldn’t use.”

There are multiple factors influencing calcium absorption from sunlight and vitamin D, low stomach acid caused by the inappropriate use of acid lowering drugs and even the common use of cheap forms of calcium that the body simply doesn’t recognise.

The evidence on calcium supplements and potential harms is not entirely straightforward. The US Preventive Services Task Force has found that vitamin D and calcium supplementation can increase the incidence of kidney stones, although it assessed the magnitude of the harm as small. Meanwhile, the broader evidence on calcium supplements and cardiovascular disease remains mixed, meaning claims that supplementation generally causes hardened arteries should be treated cautiously.

So what should people do instead?

Blood tests or urinalysis are the main way to diagnose vitamin deficiencies. Healthcare providers, especially primary care providers, may recommend these tests based on symptoms you have. Routine blood work during an annual checkup or physical exam can also catch many deficiencies before you have symptoms, as the experts say.

 Five questions to ask before buying another supplement

 Before reaching for another bottle, Leonetti suggests consumers ask themselves five questions:

 Has the product triggered any health warnings or sanctions?

 Has the product been tested by independent labs?

 Is the product too good to be true? .

 Is there evidence that the supplement does what it promises?

 Do I really need supplements?

 The takeaway is not that every supplement is unnecessary, or that people should stop taking supplements prescribed or recommended for a genuine deficiency. Instead, a brightly coloured bottle on a pharmacy shelf, or a convincing search result online, cannot tell you what your body actually needs.

 Before adding another pill, powder or capsule to your daily routine, the more important question may be the simplest one: Do you know why you are taking it?

Lakshana is an entertainment and lifestyle journalist with over a decade of experience. She covers a wide range of stories—from community and health to mental health and inspiring people features.

A passionate K-pop enthusiast, she also enjoys exploring the cultural impact of music and fandoms through her writing.