Expert reveals how to spot the hidden ‘gunk’ in vitamin pills: ‘Can cause laxative effects or stop absorption’

There has never been more supplements lining supermarket shelves, packed into bathroom cabinets and stacked on night stands as millions endeavour to boost their health through a daily pill or powder. 

Over half of adults in the UK take some form of supplement regularly—the equivalent of 81 million supplements a day. 

Made by isolating essential minerals and vitamins from plant and animal compounds, it’s easy to assume that all supplements are good for us—whether we’re looking for a better night’s sleep, more energy or an immunity boost. 

But, experts warn that they can be packed full of additives, e-numbers and emulsifiers, known as ‘filler ingredients’, that could be wreaking havoc on your health—with research linking them to bowel disease, heart disease and even cancer. 

And these fillers can also be really bad for our gut microbe, the friendly community of bacteria vital for our physical and mental health, experts warn. 

In the UK, food supplements are regulated under the Food Supplements Regulations Act 2003, which mandates compliance with general food safety legislation, meaning that supplement companies cannot make misleading health claims. 

But, unlike medicines which are routinely tested for any unwanted side-effects, supplements are not held to the same gold standard—meaning that they don’t always do what they say on the tin. 

‘The reason additives are used in supplements so often is to bulk up powders,’ Matt Jarosay, registered nutritionist and founder of ELIVIDE supplements explained. 

‘Filler reduces the cost per capsule, which stretches the yield, but this comes at a cost to your health. Remember, whilst synthetic forms of vitamins might be 10 times cheaper, they are much harder to absorb.’

The warning comes as  popular supplements sold on Britain’s high streets were found to contain more than double the safe upper limit of vitamins and minerals recommended by UK health officials. 

Some were even more than 12 times permitted levels.  

So, which ‘fillers’ should we be concerned about and how do we know which supplements are safe? 

Artificial sweeteners and colourings 

Artificial sweeteners, like aspartame, are among the most common additives in the world. Calorie-free, they’re used in thousands of ultra processed foods and even supplements to enhance taste and flavour. 

But experts have tirelessly raised concerns about their safety, with aspartame listed by the International Agency for Research on Cancer (IARC) as ‘possibly carcinogenic’. 

Supplements including Tesco’s chewable vitamin C, Morrison’s orange flavour chewable vitamin C and Boot’s vitamin C orange flavour chewable tablets have previously listed the artificial sweetener in their ingredients. 

Other studies have even implicated the sweetener in the buildup of fat in the arteries, which increases the risk of heart attack and stroke.

This collection of fat deposits, called atherosclerosis, leads to the arteries narrowing, restricting the flow of blood to and from the heart, damaging the organ over time.

Parts of the fatty plaque can break off triggering dangerous blockages in blood vessels, risking heart attack and stroke. 

‘Titanium dioxide is among the worst additives out there,’ Mr Jasory added. 

‘It’s being phased out, but is still used; it gives supplements a bright appearance, but disrupts gut barrier integrity.’ 

Emerging evidence suggests aspartame may also disrupt the gut microbiome, the collection of healthy bacteria in the body that play a key role in digestion, immunity and even mood.

This disruption can negatively affect digestive health and immune function, potentially increasing the risk of other health issues with experts increasingly making a connection between the gut microbiome and colon cancer, saying an unbalanced microbiome may increase the risk of the disease. 

Anti-caking agents 

Look out for names like maltodextrin, guar gum, and magnesium stearate, a ‘flow’ agent which in high quantities can have laxative effects and impact nutrient absorption, Mr Jarosy advised. 

Magnesium stearate is often used in the manufacturing process to prevent ingredients from sticking to equipment and machinery. 

And whilst the Food Standards Agency (FSA) considers it safe for use in supplements, experts say it could interfere with absorption of nutrients—rendering your supplements useless. 

‘All of these can cause some level of irritation in the gastrointestinal system’, the nutritionist cautioned. 

‘The issue isn’t usually one single small dose, but the ‘cocktail cumulative’ effect over a lifetime. 

‘Most people are already suffering from a significant amount of gut irritation, which is why gut issues are the number one problem we address as nutritional therapists, so not adding more burden is something to be mindful of,’ he added.  

Reduced bio-availability: the capsule shell 

One of the main issues with using additives in supplements is that they can actually block the absorption of key nutrients. 

For example magnesium stearate is hydrophobic, Mr Jarosy explained. 

‘This ultimately means it can delay disintegration, potentially causing reduced absorption. Dicalcium phosphate can also reduce the bioavailability of some minerals, like zinc, by forming complexes or competing for transport pathways.’ 

Another thing most people forget about is that the vitamins are what is actually inside the capsule, and not the supplement as a whole, Mr Jarosay says. 

‘Most supplements use  Hydroxypropyl Methylcellulose (HPMC), otherwise known as vegetable cellulose which is actually semi-synthetic and typically derived from wood pulp. 

‘Whilst it doesn’t always cause issues it can cause some gut upset, especially if you’re taking multiple capsules,’ he said.  

What to look out for

The first thing to look out for is a transparent and detailed ingredient list when it comes to buying clean supplements, Mr Jarosy explained. 

It should include the specific form of the vitamins included—for example whether its vitamin D2 or vitamin D3, which is  considered slightly more effective—as well as the amount. 

This is particularly important as most adults will be able to get most of the essential vitamins and minerals they need from their diet—with the exception of vitamin D in the winter months—meaning that heavy supplementation could lead to an overdose. 

‘You can also look at what nutrient forms the manufacturer is using, which is a bit of a telltale for their manufacturing quality,’ Mr Jarosy said. 

‘For example, if a company is using citrate mineral forms, like zinc citrate, or Pyridoxine Hydrochloride instead of Pyridoxal-5-Phosphate, the active form, for vitamin B6, then you know they are cutting corners.’