Many people take multiple supplements daily, often combining multivitamins with single-ingredient products. According to Prof Dr Chee, Professor in Nutrition and Dietetics, the concern is that excessive vitamin or mineral intake can pose health risks, particularly with fat-soluble vitamins like A, D, E, and K, which tend to be stored in the body rather than excreted.

“Consumers should first be aware of the recommended intake levels for vitamins and minerals, which can usually be found on government health education platforms or clarified by dietitians and nutritionists. If you choose to take a supplement, don’t exceed the recommended intake levels or the upper limit. Ideally, a dietitian or nutritionist should assess whether your diet is truly lacking before you decide to supplement,” says Prof Dr Chee.

Excessive intakes of water-soluble vitamins such as vitamin C are generally excreted in urine, but fat-soluble vitamins are more likely to build up in the body. Too much vitamin A may be harmful during pregnancy, vitamin E can increase bleeding risks when combined with anticoagulants, and vitamin K may reduce the effectiveness of warfarin in people with heart disease.

It’s also important to pay attention to the Tolerable Upper Intake Levels, which are about 3,000 mcg for vitamin A, 100 mcg for vitamin D, and 1,000 mg for vitamin E. Sticking to the Recommended Daily Allowance (RDA) and consulting a physician if you’re on medication or have underlying health conditions is strongly advised.

Many people believe that “more is better” when it comes to vitamins, but chronic over-supplementation can have serious and often overlooked consequences, particularly for individuals with long-term health conditions such as kidney disease, heart problems, or diabetes.

Chronic kidney disease (CKD)

• Vitamin A: When kidney function is reduced, vitamin A builds up more easily in the body. This can lead to liver toxicity, bone loss, and intracranial hypertension (raised pressure in the brain causing headaches and vision changes), even at moderate doses.
• Vitamin C: Excess vitamin C may convert to oxalate, which increases the risk of kidney stones. CKD patients are especially vulnerable to this effect.
• Magnesium and potassium: Often marketed as natural laxatives or electrolyte supplements, but in CKD they can accumulate. This may cause hypermagnesaemia (too much magnesium leading to weakness, low blood pressure, and heart block) or hyperkalaemia (too much potassium, which can lead to dangerous heart rhythm disturbances).
• Chromium picolinate: High doses have been linked to both kidney and liver injury, making it a particular concern for people with CKD.

Heart disease or arrhythmia

• Vitamin E: High-dose use (≥400 IU/day) has been linked to haemorrhagic stroke (bleeding in the brain), worsening heart failure, and increased bleeding when combined with blood-thinning medicines such as warfarin or antiplatelets.
• Vitamin K: Can interfere with warfarin, destabilising INR (a measure of blood clotting) if intake is inconsistent.
• Calcium (supplements, not food sources): Linked to possible heart attack and vascular calcification (hardening of blood vessels). Excess may also trigger arrhythmias (irregular heartbeats).
• Fish oil/omega-3: While generally beneficial at moderate doses, very high intakes can increase atrial fibrillation risk (irregular rapid heartbeat) and bleeding tendency.

Diabetes and metabolic disease

• Niacin (vitamin B3): Can worsen insulin resistance, raise glucose and uric acid levels, trigger gout, and cause liver toxicity, particularly with sustained-release forms.
• Vitamin C (high dose): May distort blood glucose readings and increase oxalate, raising kidney stone risk.
• Selenium: Chronic excess linked to brittle hair and nails, gastrointestinal upset, and possibly an increased risk of type 2 diabetes.
• Chromium: Marketed for blood sugar control but, at high doses, may harm the kidneys and liver without proven benefit.
• Cinnamon and “natural” blends: Some contain coumarins (compounds that can damage the liver), which can be especially problematic for people on statins or with existing liver disease.

General long-term risks

• Vitamin B6 (pyridoxine): Chronic high intakes (50–100 mg/day) can cause nerve damage, leading to numbness, burning, and problems with walking.
• Folate (B9): High doses may mask vitamin B12 deficiency, delaying diagnosis and risking irreversible nerve damage.
• Vitamin A: Excess can cause liver toxicity, hair loss, dry skin, headaches, bone weakness, and is particularly dangerous during pregnancy.
• Vitamin D: High intakes can lead to hypercalcaemia (too much calcium in the blood), with symptoms such as constipation, frequent urination, kidney stones, confusion, and arrhythmias.
• Iron: May cause oxidative stress, gastrointestinal injury, infections, and iron overload (excess iron storage in the body), particularly in people with certain conditions such as haemochromatosis.
• Zinc :Can deplete copper, leading to anaemia (low red blood cell count), immune suppression, and nerve damage; may also reduce HDL cholesterol (the “good” cholesterol) at high doses.
• Iodine: Both deficiency and excess can trigger hypo- or hyperthyroidism (under- or overactive thyroid), especially in those with autoimmune thyroid disease.

Supplements are often seen as harmless, but their long-term and cumulative effects can be significant. People with chronic conditions are especially at risk, and the safest approach is to consult a healthcare professional before adding or combining them.

Many people assume supplements are harmless, but from a clinical perspective it’s possible to recognise when the body is getting too much. Prof Dr Chee explains that nutrient-specific warning signs often emerge when supplementation is excessive, though they can easily be mistaken for other health issues.

For vitamins, some of the clearer red flags include:

• Vitamin A (fat soluble): Dry skin and lips, hair loss, headaches, blurred vision, bone pain, and raised liver enzymes. In pregnancy, excess vitamin A can increase the risk of birth defects.
• Vitamin D: Symptoms of hypercalcaemia, such as constipation, abdominal pain, kidney stones, confusion, weakness, or abnormal heart rhythm.
• Vitamin E: Easy bruising and bleeding, which may worsen if taken alongside anticoagulant medicines.
• Vitamin K: Very high intakes can reduce the effectiveness of warfarin, leading to unstable blood clotting.
• Vitamin B6 (pyridoxine): Tingling or numbness in the hands and feet, often symmetrical, and balance problems even with moderate long-term use.
• Niacin (B3): Flushing, itching, liver injury, and worsening of glucose or uric acid levels.
• Vitamin C: Gastrointestinal upset, and in susceptible individuals, kidney stones.
• Biotin: While not known to cause toxicity, it can interfere with thyroid laboratory tests.

Minerals may also give rise to distinct signs of excess:

• Iron: Stomach pain, constipation, dark stools, and in chronic excess, elevated ferritin and liver damage.
• Calcium: Constipation, kidney stones, calcium deposits in tissues, and irregular heart rhythms.
• Magnesium: Diarrhoea, and at very high levels, low blood pressure and lethargy.
• Zinc: Nausea and a metallic taste in the mouth.
• Selenium: Hair loss, brittle nails, skin rash, fatigue, and garlic-like breath.
• Iodine: Thyroid swelling or symptoms of under- or overactive thyroid (fatigue, palpitations, heat or cold intolerance).
• Potassium: Weakness, tingling, and dangerous arrhythmias, particularly in people with kidney disease or those on certain blood pressure medicines such as ACE inhibitors or ARBs.

“Many of these symptoms can be subtle and overlap with other conditions, which is why supplement toxicity is often overlooked,” notes Prof Dr Chee. “Anyone noticing persistent or unexplained changes while taking supplements should seek professional advice rather than assuming these products are risk-free.”

From collagen powders to immunity boosters, wellness culture often encourages people to layer on health products in the name of self-care. The challenge, as Prof Dr Chee explains, is knowing when this shifts from beneficial to excessive and whether we’re chasing ideals that the body may not actually need.

Scientific evidence for many of these supplements, such as collagen, remains weak. What people should understand is that vitamins and minerals are micronutrients, meaning the body only requires them in milligrams or micrograms, in very small amounts that in most cases can be obtained through a balanced diet. Consistently, research has shown little to no significant benefit of vitamin or mineral supplements in improving long-term health outcomes. By contrast, the evidence for eating a healthy diet is strong, with repeated findings that it’s linked to longevity, disease prevention, and overall better health.

“For example, higher intake of fish, fruits, and vegetables has been associated with lower risk of heart disease,” notes Prof Dr Chee. “This is the kind of reflection people should have before spending large sums of money on supplements that are not well proven.”

Before adding new supplements to their routine, consumers should first consider whether they truly need them. It’s especially important for those already taking multiple products or managing a chronic condition to seek medical advice rather than self-prescribing.

It’s always best to check with a doctor or dietitian before starting any additional supplements. In many cases, the nutrients people are looking for can already be met through a healthy diet. Professional evaluation helps to avoid unnecessary products, interactions with existing medicines, and potential harm.