Taking several supplements at once: is too much harmful?

Taking several supplements at once has become an everyday habit in Estonia and elsewhere in the world. Studies show that a significant share of adults use four or more supplements at the same time (Bailey et al., 2011). Whether such combining is safe is a perfectly fair question – and the answer depends on which substances end up together and in what amounts.

How does taking several supplements at once affect the body?

Supplements fall into two main groups: water-soluble (vitamin C, B vitamins) and fat-soluble (vitamins A, D, E and K). This distinction is key when assessing safety.

Water-soluble vitamins do not accumulate in the body to any great extent – the excess is excreted in urine relatively quickly. Fat-soluble vitamins, on the other hand, are stored in adipose tissue and the liver. Long-term overdosing on them can lead to toxic concentrations. In vitamin D poisoning (hypervitaminosis D), for example, blood calcium rises to dangerous levels, which can cause nausea, weakness and kidney damage (Marcinowska-Suchowierska et al., 2018).

Much like with eating habits – as the article Why we sometimes eat too much explains – more does not automatically mean better. The body processes nutrients at a set pace, and the excess has to go somewhere: it is excreted, stored, or interacts with other substances.

Which supplements don’t go well together?

One of the best-documented mineral interactions is the relationship between iron and calcium. Hallberg et al. (1991) showed that 300–600 mg of calcium (whether from milk or a supplement) reduces the absorption of both heme and non-heme iron by roughly 30–50%. Practical advice: don’t take an iron supplement and a calcium supplement at the same time – allow a gap of at least one to two hours.

Another well-known problematic pair is zinc and copper. Long-term use of high doses of zinc (over 50 mg a day) interferes with copper absorption, which over time can end in copper deficiency (Fosmire, 1990). Typical supplement doses (10–25 mg of zinc a day) do not usually pose this risk, but when you add up zinc from several sources, it’s worth checking the totals.

With fat-soluble vitamins, there is an added risk that several products contain the same substances. A multivitamin combined with a separate vitamin D product and fish oil easily gives you three sources of vitamin D, whose sum can exceed the recommended daily upper limit.

When do too many supplements become dangerous?

The European Food Safety Authority (EFSA) has set a tolerable upper intake level (UL) for most vitamins and minerals – the amount that can be consumed daily without a documented risk of adverse health effects. For example, the UL for vitamin A is 3000 µg retinol equivalents (RE) a day for adults; for vitamin D it is 100 µg (4000 IU). These limits can be found on the EFSA website.

Interactions with sunlight are also worth considering. As the article Is sunbathing harmful explains, the skin produces vitamin D under ultraviolet radiation – during the active summer season this can reduce the need for supplements. On the other hand, people who take a full dose of a vitamin D supplement without taking the effects of sunbathing into account can exceed the amount considered safe.

Sport and an active lifestyle often set the stage for using several supplements at once – protein supplements, creatine, vitamins and minerals can all end up in your diet together. The experience of athletes – such as Happy birthday, Ott from our community – shows that being well informed is the basis of success. The NIH (US National Institutes of Health) stresses that checking interactions is especially important when prescription medications are taken at the same time – for example, vitamin K and anticoagulants, or iron and thyroid medications.

How to take several supplements at once safely?

The following practical steps help minimize the risk:

1. Add up the amounts – check the label of each product, find the daily amount of each nutrient and add up the amounts of the same nutrient from all sources.
2. Account for absorption interactions – take iron and calcium at different times; fat-soluble vitamins (D, K, E, A) are absorbed better with a meal that contains fat.
3. Don’t exceed the EFSA upper limits – these are specific numerical thresholds, and staying below them is a safety net.
4. Consult a doctor if you take prescription medications or if the list of products you use is long – a pharmacist’s advice is free and quick here.
5. Do a periodic review – every six months it’s worth checking whether all the supplements you started are still needed.

In summary: taking several supplements at once is generally safe as long as the amounts stay within the recommended range and the main combinations that interfere with absorption are taken into account.

References

• Bailey RL, Gahche JJ, Lentino CV, et al. (2011). Dietary Supplement Use in the United States, 2003–2006. J Nutr. 141(2):261–266. PMID: 21865568
• Hallberg L, Brune M, Erlandsson M, et al. (1991). Calcium: Effect of different amounts on nonheme- and heme-iron absorption in humans. Am J Clin Nutr. 53(1):112–119. PMID: 1985404
• Fosmire GJ (1990). Zinc toxicity. Am J Clin Nutr. 51(2):225–227. PMID: 2407097
• Marcinowska-Suchowierska E, Kupisz-Urbańska M, Łukaszkiewicz J, et al. (2018). Vitamin D Toxicity–A Clinical Perspective. Front Endocrinol (Lausanne). 9:550. DOI: 10.3389/fendo.2018.00550
• EFSA Panel on Dietetic Products, Nutrition and Allergies (2006). Tolerable Upper Intake Levels for Vitamins and Minerals. European Food Safety Authority. ISBN: 92-9199-014-0

Come and train! ArtGym