Supplements are everywhere right now. A quick trip to the chemist or a few minutes on social media is enough to bring up claims that vitamins can improve skin, increase energy levels and even help hold back the signs of ageing.
Health professionals, however, say there is a downside to this growing obsession. Taking more than your body actually needs can create real medical problems, with possible effects including nerve issues, heart complications and even hair loss.
Dr Tina Ghela from Medichecks says this is not a rare problem.
“Over supplementing can absolutely have negative health effects,” she explains.
“This can be anything from nausea, diarrhea, difficulty sleeping to even mild nerve damage, amongst other things.”
She stresses that for many people, extra tablets are unnecessary in the first place.
“There are 13 essential vitamins that we should all be getting into our diet on a regular basis, but most people will get all the vitamins and minerals they need through eating a healthy, balanced diet.”
That broadly matches public health advice. The CDC says vitamins and minerals are essential for health, but also notes that healthy eating patterns built around nutrient-dense foods are the foundation of good nutrition. In the US, federal survey data published by the CDC and NIH found that dietary supplement use is common, with nearly three in five adults reporting use in 2017 through March 2020, which helps explain why experts are increasingly concerned about people unknowingly stacking several products at once.
Dr Ghela also notes that a lot of common foods are already fortified with added nutrients. That means some people may be consuming more vitamins and minerals than they realise, even before adding supplements into the mix.
Another issue, she says, is the constant pressure from skincare trends, wellness marketing and anti-ageing advice online. This can encourage people to combine multiple products without thinking about how much of each ingredient they are taking overall.
“Most people don’t realize that they are even overdosing,” she says.
“We are so wired to believe that we need to get our daily vitamin and mineral intake that the thought of over supplementing doesn’t cross our minds.”
Her guidance is simple: avoid doubling up.
“If you are taking a multivitamin, do not take any other ‘wellbeing’ supplements,” she warns, adding that anyone considering vitamins should speak to a medical professional first rather than self-prescribing based on social media recommendations.
One of the biggest problems is that “too much” does not just mean one huge dose. It can also mean repeatedly going over the tolerable upper intake level, the maximum average daily intake that is unlikely to pose a risk for most healthy people. Those limits include nutrients from supplements, fortified foods and, in some cases, the rest of the diet too.
When someone takes too many supplements over a prolonged period, the consequences can show up in several areas of the body.
Possible warning signs include nausea, vomiting, tiredness, dizziness, rashes, muscle weakness and hair loss, although the exact symptoms depend on which vitamin is being consumed in excess.
Dr Ghela highlights five vitamins and minerals that can be especially problematic when intake gets too high. Vitamin C, despite its harmless reputation, may lead to nausea and diarrhea if overused. The NIH lists 2,000 mg a day as the upper limit for adults, and stomach upset is one of the better-known signs of going overboard.
Selenium, which appears in many general health supplements, can cause fatigue, stomach upset, hair loss and in some cases nerve damage. According to the NIH, too much selenium over time can also cause garlic-smelling breath, a metallic taste, brittle hair or nails, skin rashes and irritability. In very high amounts, it has been linked to tremors, kidney failure, heart attack and heart failure. The adult upper limit is 400 micrograms a day.
Vitamin D is more complicated. Many people, especially during winter, do not get enough of it, so supplementation can be useful and sometimes recommended.
Even so, Dr Ghela says it is one of the more worrying nutrients to overdo. Going beyond the safe upper daily amount may contribute to serious heart issues and a calcium build-up that can damage the kidneys and bones. The NIH says vitamin D toxicity is almost always caused by excessive supplement use rather than sun exposure, and in adults the upper limit is 100 micrograms or 4,000 IU a day unless a clinician recommends otherwise. Very high blood levels can trigger nausea, vomiting, confusion, excessive thirst and urination, kidney stones, irregular heartbeat and, in extreme cases, kidney failure.
Vitamin A and beta-carotene come with a particularly unusual effect, too much can make the skin take on an orange tone. More specifically, long-term excess beta-carotene can cause carotenodermia, a yellow-orange discolouration of the skin that is usually harmless and reversible. Preformed vitamin A is the more serious concern because high long-term intakes have been associated with liver abnormalities and other toxic effects. For adults, the upper limit for preformed vitamin A is 3,000 micrograms RAE a day.
Meanwhile, too much Vitamin K, although deficiency is uncommon, may affect blood clotting and increase the risk of bleeding.
There is an important nuance here, though. The NIH has not set a formal upper limit for vitamin K because toxicity from food or supplements appears to be low in healthy people. The bigger issue is interaction with medication. Vitamin K can have a serious effect on anticoagulants such as warfarin, and sudden changes in intake can make those medicines work less well or too strongly. For people on blood thinners, consistency matters more than taking extra.
The CDC advises people to think about whether their normal diet is already covering their nutritional requirements before starting any supplement. Reading labels carefully also matters, because a multivitamin, an immunity powder and a hair or skin supplement can all contain the same nutrients in overlapping doses.
Experts generally recommend getting most nutrients from food first and using supplements to fill a proven gap rather than as a catch-all wellness habit. Anyone with persistent symptoms such as nausea, unexplained hair loss, weakness, confusion, excessive thirst or tingling should stop guessing and speak to a pharmacist or doctor, especially if they are taking more than one product or also use prescription medication.
Medichecks offers a Health and Lifestyle blood test for people who want to check whether their diet is already meeting their needs before adding another supplement.