When vitamins turn toxic: Why more is not always better

Published on 7 October 2025

Supplements are often seen as a safe way to boost health, but fat-soluble vitamins and minerals can build up to toxic levels in the body. We explore how much is too much, what the risks look like, and how to avoid crossing the line.

From pharmacy shelves to online stores, the sheer variety of supplements shows how firmly they have become part of many people’s daily routines. 

Supplements like multivitamins, vitamin C, and fish oil are often taken to “boost” health, and have become increasingly popular, particularly among those with busy lifestyles who struggle to maintain a balanced diet. 

For most people, a standard daily multivitamin taken at the recommended dose is unlikely to cause harm. The real concern comes when people take high doses of multivitamins for long periods or combine several different products without medical advice.

There is a crucial reality to keep in mind. “Taking supplements unnecessarily can lead to toxicity,” said Ms Rachel Tok, Dietitian, Department of Dietetics, National University Hospital (NUH).

The problem is not usually with water-soluble vitamins such as vitamin C and the vitamin B group, which are typically flushed out in urine when taken in excess. Rather, the greater risk lies with fat-soluble vitamins – A, D, E and K – and certain minerals. As these are stored in the liver and fatty tissues, they can accumulate to harmful levels if taken beyond the body’s needs, Ms Tok explained.

When ‘more’ backfires 

For instance, vitamin A toxicity can present with symptoms that range from nausea and vomiting to liver damage, Ms Tok said. “Additionally, excessive calcium may result in calcification of our soft tissues, kidney stones, as well as interference in the absorption of other nutrients such as iron,” she added.

These risks are not confined to prescription products. Over-the-counter options can also pose problems when people combine multiple preparations or take mega-doses. “If needed, taking daily vitamins according to recommended doses on the packaging is a generally safer option as they tend to contain lower doses,” she added. 

“In general, people should take caution when taking supplements especially without the advice of a healthcare professional,” Ms Tok said.

A mindful approach

The safest and most effective way to prevent deficiencies is still through eating well. “Ensuring a healthy balanced diet with varying food sources from the different food groups, including wholegrains, protein, fruits and vegetables, and dairy and calcium-rich sources can help to provide nutritional adequacy without the need for supplementation,” said Ms Tok.

Small lifestyle tweaks can also help. “Spending five to 30 minutes in the sun between 10am and 3pm, twice a week, helps the body produce vitamin D,” Ms Tok said. “Pairing meat with vitamin C-rich fruits increases iron absorption. And separating dairy from iron-rich meals by at least one to two hours allows both nutrients to be better absorbed.” 

Still, supplements may be necessary in certain groups. For instance, nutrient absorption can begin to decline from around age 40, and usually becomes more pronounced after 70. This raises the risk of deficiencies in vitamins D and B12, calcium, and iron. 

Pregnant women and those with chronic conditions may also have higher requirements. In such cases, supplements can help, but the approach should be targeted and guided by a healthcare professional, not self-prescribing from the pharmacy aisle. 

In general, supplements are useful when prescribed for a specific need but are not necessary as a daily habit in healthy persons. If in doubt, ask your doctor rather than guessing at the pharmacy shelf.

In consultation with Ms Rachel Tok, Dietitian, Department of Dietetics, NUH.