Mixing vitamins? UAE doctors explain risky supplement combinations

The morning routine may look like a picture of health: A multivitamin with breakfast, vitamin D because 'everyone needs it', iron because of tiredness, calcium for stronger bones, zinc for immunity and perhaps a beauty supplement for the hair and nails.

Each bottle appears to have a clear purpose, and each promises to fill a gap. However, doctors warn that the problem often begins when supplements are treated as harmless additions to daily life. When multiple products are combined, nutrients can overlap, compete for absorption, interfere with medicines or push certain vitamins and minerals beyond what the body needs.

The danger, experts say, is not always obvious. A person may believe they are supporting their health, while unknowingly reducing the effectiveness of medication or creating new problems.

As Dr. Jaspreet Kaur, Specialist Internal Medicine at RAK Hospital explains, taking supplements without knowing what your body needs, can actually be dangerous at times, because sometimes they can mask the symptoms. "The root cause can go undetected and unaddressed for long,” says Dr. Jaspreet Kaur.

If a person is taking medication, supplements may interfere with how those medicines work, which can dilute their impact. That is why it is important to consult a doctor and address the underlying cause before starting any supplement blindly.

Unlike food, which contains nutrients in complex combinations, supplements often deliver concentrated doses of individual vitamins and minerals. This can lead to unexpected interactions.

As Dr Kaur explains, dietary supplements are biologically active compounds which can alter how prescription drugs are cleared from the body and they can block the absorption of other vital nutrients. Furthermore, these supplements should not be viewed as harmless, just because they're available without prescription.

They can interfere with prescription medicines, worsen medical conditions, block the absorption of other nutrients, as vitamins and minerals can act like potent drugs. When all of them combine, without medical guidance, it alters the medication potency and trigger severe side effects, or cause deficiencies.

Iron and calcium are essential: But taking them together, might just reduce the iron absorption. And that's particularly relevant for people taking iron supplements for a confirmed deficiency, as Dr Kaur explains.

The timing of supplements can therefore matter as much as the supplement itself.

People taking thyroid medication should also be particularly careful. “Thyroid medications - ( levothyroxine ) and iron tablets if taken together can reduce the absorption of thyroxine leading to u controlled hypothyroidism,” elaborates Dr Kaur.

For patients managing chronic conditions, adding supplements without discussing them with a healthcare professional can unintentionally affect treatment.

Research has found that taking calcium and iron together can reduce iron absorption. A 2021 systematic review and meta-analysis published in The Journal of Nutrition found that higher calcium intake was linked to reduced iron absorption in short-term studies. However, researchers noted that the long-term impact on measures such as haemoglobin levels was less clear.

This does not mean everyone taking calcium and iron together will develop iron deficiency. Rather, it highlights why timing and dosage matter, particularly for people taking iron supplements to correct a confirmed deficiency.

Vitamin K is important for normal blood clotting, but it can interact with medicines designed to prevent clots. People taking blood thinners such as warfarin need to be particularly cautious before adding vitamin K supplements.

"They both act the opposite making one prone to increased clots if take in the same person,” says Dr Kaur.

The concern is not that Vitamin K is harmful, it is that changing Vitamin K intake without medical guidance can affect how certain medicines work.

Vitamin E is often marketed for its antioxidant and beauty benefits, but high doses may not be suitable for everyone. People taking antiplatelet medications should also exercise caution with vitamin E supplements. Dr Kaur notes that taking vitamin E alongside such medicines without medical guidance may increase the risk of bleeding.

Hence, experts advise people taking medication that affects bleeding or clotting to check before adding supplements marketed for wellness or skin health.

Zinc has become a popular ingredient in immunity supplements, especially during cold and flu season. However, taking high doses of the mineral might affect the body's balance. As Dr Kaur warns, iron should not be combined with calcium, and neither should Vitamin C, and Vitamin b12, as well as Vitamin E and K, or zinc with copper.

Jamie Richards, Valeo Health Chief Wellbeing Officer and Clinical Psychoneuroimmunologist, explains why balance matters. “Where is the balance? Our body likes to live in harmony. Too much of certain supplements, especially minerals, can block and interfere with other equally important nutrients.”

When multiple supplements with overlapping ingredients are combined, paired with a daily multivitamin, it can result in high toxicity levels, which impact the kidneys. The person could be prone to kidney stones, weak bones, and more prone to fractures, gut issues and oxidative stress in the body, explains Dr Kaur.

Many people assume that if a vitamin is good for the body, taking more of it must be even better. But as experts warn that vitamins and minerals only work within a certain range, and excess amounts can cause harm.

Excess of anything is harmful, as Dr Kaur adds, and that applies to vitamin and minerals. "Each and every vitamin and mineral needs to be in a specific range in our body to let the homeostasis of the body be maintained,” says Dr Kaur.

Taking too much of certain nutrients can affect vital organs, including the liver, kidneys, brain, bones and gut.

Experts also caution that fat-soluble vitamins, including vitamins A, D, E and K, require particular care because they are stored in the body instead of being easily eliminated. "Too much of any of these, can increase the level of toxicity, overworking the kidneys and livers, when it comes to filtering waste,” says Richards.

Why it matters: Unlike water-soluble vitamins, which the body can generally remove through urine when consumed in excess, fat-soluble vitamins can accumulate over time and increase the risk of toxicity.

Fatigue is one of the most common reasons people begin taking supplements. Many people self-prescribe vitamin B12, iron, vitamin D, CoQ10 or herbal products hoping for more energy.

But experts warn that tiredness is not always caused by a vitamin deficiency. If the person does not have a documented deficiency, taking extra vitamins will not provide an energy boost. The unabsorbed water-soluble vitamins will be excreted in the urine, and the excess of the fat-soluble vitamins accumulate and risk toxicity.

Instead, supplements may delay finding the actual cause. “Rather taking them over the counter, can mask serious conditions like hypothyroidism, obstructive sleep apnea, or chronic conditions.”

Richards describes how people can accidentally create a new problem while trying to solve an old one: “Imagine you have a genuine nutrient deficiency; it’s causing you to feel unwell. You take a supplement to correct the deficiency and feel better. You like feeling better so you continue to take it. Before too long you begin to feel unwell, except this time it’s because you now have too much and you’ve inadvertently created a new problem. But it can’t be the supplement, because you trust the supplement, after all it made you feel better.”

Dr Kaur says supplementation should begin with understanding why it is needed.

She advises: Before adding any dietary supplement to your daily routine, consult a doctor and take it only if a deficiency has been confirmed. Ensure you follow the recommended dosage, especially if you are taking long-term medications, as some supplements may need to be spaced out to prevent interactions and side effects. It is also important to choose certified, reliable products.