Almost half of Australians take dietary supplements and vitamins, but experts have warned it may be doing you more harm than good – especially if you’re self-medicating with products bought without a doctor’s oversight.

If you ingest too many Vitamin A capsules, for example, you may experience skin peeling, liver impairment and loss of vision.

But you won’t read that on the packaging.

Unlike prescription medicine, dietary supplements that you can buy of your own accord aren’t required to tell you about their potential side effects, what could happen if you take them with other drugs and supplements, or the risk of overdosing.

This is the warning from Geraldine Moses, whose paper about the potential harms of vitamins and minerals was released on Monday.

“Risk often comes from cumulative toxicity from multiple products that people take,” said Dr Moses, from the University of Queensland’s School of Pharmacy.

Even if you have a small dose of one product, the cumulative dose from taking many different supplements can be “gigantic”, Dr Moses told The New Daily.

“Multivitamins contribute as much to potential harm as any product.”

She often sees cancer patients taking up to nine multivitamins because they think each one is having a different effect.

“They haven’t paid a whole lot of attention to the ingredients, not realising that it’s all the same stuff, just rejigged,” Dr Moses said.

About 47 per cent of Australians take dietary supplements. One of the reasons they are so popular is because of the false belief they are harmless.

“What many people don’t realise is that high doses of some supplements can be dangerous,” Dr Moses said.

“The same vitamin or mineral can be in multiple different products, so a person can accidentally overdose if those products are all taken together.”

Dr Moses listed six potential harms of dietary supplements:

• You can experience adverse effects from short or long-term use and taking a high or low dose
• The supplement can make other drugs more toxic or less effective
• Supplements can be expensive. Your money could be better spent on other treatments or essential items that may be more effective
• The time you spend taking ineffective products may delay more effective interventions, waste valuable time, and allow for a disease or illness you might have to progress
• They can give you false hope and leave you feeling disappointed if they don’t work
• You may be unnecessarily adding to the number of medicines you are taking and therefore, increasing the risk of a medication error, and drug interactions, which can result in adverse effects.

Dr Moses also listed some potential adverse effects of these commonly used vitamins and minerals:

• Vitamin A: Skin desquamation, liver impairment, loss of vision and severe intracranial hypertension
• Vitamin B3: Skin flushing, burning sensation, pruritus, hypotension and vasodilation in the eye resulting in toxic cystoid macular oedema
• Vitamin B6: Severe sensory peripheral neuropathies
• Vitamin C: Kidney stones
• Vitamin D: Hypercalcaemia, increased risk of falls and fracture in the elderly, with symptoms from thirst and polyuria to seizures, coma and death
• Vitamin E: Haemorrhagic stroke
• Calcium: Gastric reflux, constipation, vascular and soft tissue calcification, hypercalciuria, kidney stones and secondary hypoparathyroidism
• Magnesium: Diarrhoea, nausea, abdominal cramping
• Zinc: Altered or impaired taste and smell, anosmia
• Selenium: Hair and nail loss or brittleness, lesions of the skin and nervous system, nausea, diarrhoea, skin rashes, mottled teeth, fatigue and mood irritability.

There’s a common belief that if it is a vitamin or mineral, “the body will somehow know what the maximum dose is that it needs and it will just magically excrete what it doesn’t need”, Dr Moses said.

However, that is incorrect.

Dr Moses said they can still be toxic, even if they’re water-soluble.

Nothing is better than food

Dietitian Stephanie Pirotta, a research fellow at Monash University and owner of Womanly Nutrition and Dietetics, said it’s important to tell your GP if you are taking any supplements.

“Even in some multivitamins, there could be nutrients that actually compete with each other,” Dr Pirotta told The New Daily.

Our body metabolises and absorbs food the best.

“Supplements are made in the lab. Whether they’re scientifically proven or not, food is always best,” she said.

“And then if supplements are needed, for whatever reason … always check again with the GP, but also your dietitian, because there are some supplements that are more evidence-based than others.”

Ultimately, there are few benefits to taking dietary supplements and a range of potential risks, Dr Moses said.

“Consumers should be aware that there is no case for vitamin or other supplements in normal healthy people, who are not pregnant or breastfeeding and are consuming a healthy diet,” she wrote in her paper.