Do you need to worry about fillers and bulkers in supplements?

If you take a vitamin or supplement, you might not have given much thought to what is actually inside the pill you swallow. 

But, it's hard to ignore the marketing claims as a swathe of new supplement brands position themselves as the additive-free alternative to traditional tablets. So does it make a difference and should you care?

We explain what extras you might find in vitamin and mineral supplements, why they're used, and whether you need to worry about them.

Eat well, live better, stay healthy – sign up for our free monthly Food & Health newsletter for the latest insights delivered straight to your inbox

What are bulkers and fillers and why are they used?

Bulkiers, fillers and additives are generally harmless and often fulfil a useful role in helping deliver active ingredients safely and effectively, much like they do for medicines.

This may be delivering the active ingredient to you in the best possible state, in a form that is easy to swallow or has a decent shelf life. 

Bulking agents may be used because the active ingredient in a pill or tablet is minuscule. In order to make up a pill that is a practical, helpful size for you to take, bulkers are used. Otherwise you could be attempting to take something the size of a few grains of sand, and taking the correct dosage would be very difficult.

Fillers and binders are ingredients used to amend or improve the consistency of the final product. Some supplements may require ‘binders’ that hold the various ingredients together in a stable form, without which your tablet would crumble and fall apart. Others are used to prolong the shelf life of the product.

Finally, additives are used to add colour, flavour or texture. For example, gummy vitamins may have fruity flavours to make them taste more appealing.

So, bulkers and fillers are inactive ingredients that may be added to a product for a variety of legitimate reasons. However, some supplements may use more than necessary. 

This can mean there is less space for the ingredients you actually want, or that you're ingesting more extras than you bargained for, particularly if you take multiple supplements.

Shefalee Loth, Which? nutritionist and principal researcher, says:

'Some fillers have valid roles in supplements - they can create a time-release effect to ensure you get the best from the supplement, and preserve the nutrients so that you get what you're paying for. In some cases, when nutrients are present in small amounts, fillers can bulk the product so that it's a reasonable size.

'However, in some cases this is taken too far. We found supplements that contained significantly more fillers than active ingredients. None of the additives we've seen so far are harmful but some, such as PVA and talc, aren't things that most people would knowingly choose to ingest.'

In the UK, all ingredients used in both pharmaceutical products and food are subject to regulation and must be safe for consumption and not misleadingly labelled. 

However, some supplements may contain products you'd prefer to avoid. For example, some could contain ingredients that might not be suitable for dietary or health reasons, such as pork gelatin.

Best multivitamin reviews and best magnesium supplements - see our independent expert reviews, which rate each product for the amount of fillers and additives, as well as dose and bioavailability

Common supplement bulkers, fillers and additives explained

These are some of the most common fillers, bulkers and additives used in supplements, why they are used and what you need to know about them:

Bulking agents

• Magnesium silicate, or talcum powder - as a bulking agent, talcum powder - made from magnesium, silicon and oxygen - is unlikely to cause you serious harm, but it’s also not something you might choose to ingest knowingly. Food-grade talc, however, is strictly controlled and purified to remove any potential contaminants.
• Starch/rice flour Both are cheap and harmless bulking agents derived from and commonly used in a wide variety of foods.
• Lactose Lactose is a milk sugar, which when used as an inactive ingredient in medicines is generally considered safe, even for those with lactose intolerance, as the amount is so small. Lactose is naturally present in dairy products and widely used in pharmaceuticals and other foods.
• Salts Common salts used in supplements include calcium carbonate and magnesium stearate. These have several uses that include anti-caking, emulsifying and lubrication as well as being a firming agent.

Binding agents

These help to hold ingredients together.

• Guar gum/arabic gum/acacia gum These are all plant-derived and generally considered harmless in small doses, such as those found in supplements. However, they may cause digestive issues in some people, especially at a higher dose. 
• Cellulose A natural carbohydrate that makes up the walls of plant cells and is harmless. Humans cannot digest cellulose, so it largely passes through the body, althrough it can also be important in the diet as fibre. Also used as a coating agent.
• Gelatine Gelatine is derived from animals (most commonly cow or pig bones, cartilage and skin) and, while it is harmless, vegetarians and vegans may want to avoid it for dietary reasons. Depending on its source, gelatine may also not be appropriate for those following either a halal or kosher diet. Also used as a coating agent.

Anti-caking agents

These help prevent ingredients from clumping and sticking to machinery in the manufacturing process. Common ingredients include:

• Stearic acid A naturally occurring fatty acid found in meats, eggs, butter and other foods. We all consume stearic acid in our everyday diets, and it is generally considered safe. It's commonly derived from palm oil for supplements, but strict vegans may want to double check. 
• Magnesium stearate A type of salt made from combining magnesium with stearic acid, used as an anti-caking or 'flow' agent. In large doses it may have a laxative effect, but not at the level found in supplements. The Food Standards Agency (FSA) and the European Food Safety Authority (EFSA) both consider magnesium stearate safe for use in food and supplements. It may however interfere with absorption of some nutrients.
• Silicone dioxide Found in sand and, although it probably sounds like something you don’t want in your body, it’s not been shown to be harmful. As with talc, the food-grade version is highly purified and a different format to the industrial version (which is problematic if inhaled). It's also found naturally in some plant foods, including oats, potatoes and apples.
• Nu-Flow, or rice-based flow agents These are flow agents that have been derived from natural products such as rice husks or hulls and are considered safe and effective.

Colourings, coatings and flavourings

These are used to enhance the appearance or taste of supplements.

• Carrageenan (E407) Derived from seaweed and used for texture in supplements and some foods. It's often used as a vegan substitute for gelatine. The Food Standards Agency (FSA) considers it safe for use in food, but some research suggests a link to potential gastrointestinal issues, particularly inflammation, in some people.
• Titanium dioxide (E171) Used as whitening agent and colour enhancer but has been linked to potential health concerns. The EU banned its use in food in 2022, including in supplements. In the UK it's still permitted in food supplements, although this is under review. 
• Maltitol, erythritol, pectin, inulin (sweeteners) These sweeteners are all 'non-nutritive', meaning that they're designed to add sweetness to products without adding calories. They are often found in 'gummy' or chewable supplements. Although they're generally considered safe (and some, such as pectin are naturally derived), they can cause digestive discomfort such as bloating or cramping.
• Sugar Often added as a sweetener in the form of glucose, sucrose or corn syrup to improve palatability. 

Healthy living

Use our expert advice and recommendations to live your best life every day.

Get started

What to look for when buying supplements

Don't feel like you have to buy the priciest supplements around because they claim to be more pure than rivals. Most inactive ingredients are harmless, particularly in the small quantities ingested as part of a daily pill or supplement. 

However, we've found that some products do contain substantially more than others, which may mean you're paying for cheap fillers over active ingredients, and you may want to avoid certain extras - particularly if you're following specific dietary guidelines or have allergies. 

• Always check ingredient labels for any ingredients you're concerned about, whether for health or lifestyle reasons
• Be wary of overblown or scaremongering claims about ingredients. 'The dose makes the poison' is worth remembering - just because something is potentially harmful in one context doesn't mean it is when used as a food-grade ingredient in tiny amounts in a supplement.

We recommend exercising caution buying from social media, online marketplaces or unknown brands. Opt for established retailers and brands, and do additional checks on brands you aren't familiar with. 

Check the dose against NHS guidance to see whether or not it's excessive. Companies love to market 'high strength' products as a benefit, but more is not always better or indeed necessary when it comes to supplements, and in some cases it can be potentially harmful.

Supplement prices can vary considerably, with some formats such as sprays and gummies generally costing more than tablets. 

Make sure you compare the cost per dose, because if it advises taking, say, two - or in some cases as many as four tablets - per day this will mean the cost per daily dose is much more than you might expect.

How to supplement safely - more insight into the pitfalls to be aware of