Vitamins, minerals at high doses can be toxic
IF YOU were to open your medicine cabinet right now, there’s a fair chance you’d find a bottle of vitamins alongside the painkillers, plasters and cough syrup.
In 2020, the global market for complementary and alternative medicines, which includes multivitamin supplements, was estimated at $82.27 billion.
Multivitamins and mineral supplements are often marketed for their health benefits. There is a perception that supplements are harmless. But they can be dangerous at incorrect dosages.
Warning bells
Most consumers use multivitamins. But others take large doses of single nutrients, especially vitamin C, iron and calcium. As lecturers in pharmacy practice, we highlight the potential adverse effects of vitamins and minerals:
Vitamin A/retinol is beneficial for good eye health. But it can cause toxicity if more than 300 000IU (units) is ingested. Chronic toxicity (hypervitaminosis) has been associated with doses higher than 10 000IU a day. Symptoms include liver impairment, loss of vision and intracranial hypertension. It can cause birth defects in pregnant women.
Vitamin B3 is beneficial for nervous and digestive system health. At moderate to high doses it can cause peripheral vasodilation (widening or dilating of the blood vessels at the extremities, such as the legs and arms), resulting in skin flushing, burning sensation, pruritis (itchiness of the skin) and hypotension (low blood pressure). Vitamin B6 is essential for brain development and in ensuring that the immune system remains
healthy. But it can result in damage to the peripheral nerves of the hands and feet (causing a sensation of numbness or pins and needles) at doses over 200mg/daily. Vitamin C is an antioxidant and assists in the repair of body tissue. Taken in high doses it can cause kidney stones and interactions with oncology drugs.
Vitamin D is essential for bone and teeth development. At high doses it can cause hypercalcaemia (calcium
level in the blood is above normal) that results in thirst, excessive urination, seizures, coma and death. Calcium is essential for bone health, but can cause constipation and gastric reflux. High doses can cause hypercalciuria (increased calcium in the urine), kidney stones and secondary hypoparathyroidism (underactive parathyroid gland). Magnesium is important for muscle and nerve functioning. At high doses it can cause diarrhoea, nausea and abdominal cramping, and can interact with antibiotics.
Zinc can impair taste and smell, and doses over 80mg daily have adverse prostate effects.
Selenium can cause hair and nail loss or brittleness, lesions of the skin and nervous system, skin rashes, fatigue and mood irritability at high doses.
Iron at 100–200mg/day can cause constipation, black faeces, black discolouration of teeth and abdominal pain.
Recommendations
Make informed decisions based on evidence. Regular exercise and a well-balanced diet are more likely to do us good.
Seeking professional advice before consuming supplements can reduce the risk of adverse effects. Seek professional guidance if you have symptoms.
Padayachee is a senior lecturer in the Department of Pharmacy and Pharmacology at the University of the Witwatersrand. Bangalee is an associate professor of Pharmaceutical Sciences at the University of KwaZulu-Natal.
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