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Vitamin D: Can I have too much?

Dr Roger Henderson
Reviewed by Roger HendersonReviewed on 29.04.2024 | 4 minutes read

So we got the message we need vitamin D for healthy bones and teeth and heaps of other good things, and we know we need to take supplements through the dreary dark winter. But can we have too much of a good thing? Well, in a word, yes. The clinicians here at Healthwords will tell you how much is too much, what to look out for and how to protect yourself.

What can cause too much vitamin D?

Vitamin D comes from sunshine, the diet and supplements. Starting with the sunshine, your body is programmed to only convert as much vitamin D as it needs from the sun, and no more, therefore you can’t "overdose" from sunshine. However, this source only provides adequate levels of vitamin D in the winter months, hence why we need to obtain the vitamin from other sources.

Diet can provide vitamin D. Good sources include oily fish, such as salmon and mackerel, red meat, liver, eggs and dairy products. It may also be added by companies in breakfast cereals, margarine and milk – lookout for the "fortified with" label.

Supplements are recommended by the UK government for everyone throughout the dark winter months, and for others at risk of deficiency, such as those with darker skin or who are housebound. Therefore the risk of taking too much vitamin D usually comes from taking too many supplements.

How much vitamin D should I take?

The maintenance dose refers to keeping levels topped up, rather than if a blood test has shown a deficiency. The maintenance dose is 400 IU (international units) for adults, children aged 1 year and over, or those who are pregnant or breastfeeding. The label on your supplement may be expressed in micrograms, in which case 10 mcg is the equivalent dose.

Infants from birth to 12 months who are all or partially breastfed should be given supplements containing 300 to 400 IU (8.5 to 10 mcg). Formula milk is fortified with vitamin D, so these infants would only need supplements if they are taking less than 500ml (a pint) or formula per day.

Tips for avoiding taking too much

Have a look at your medicine cabinet. You may be trying to do the best for your body and are on several vitamin supplements, including multivitamins. Check whether these contain vitamin D – multivitamins and calcium supplements are the likely culprits, or those branded as "for bone health". The label will tell you whether you’re already getting your recommended daily amount (RDA)- it’s usually given as a percentage – if the answer is yes, you don’t need to add extra vitamin D supplements.

Check the label of your vitamin D supplements. If you are aiming to just keep vitamin D levels topped up – maintenance dose as we call it – this should be 400 IU (international units) per day, or 10 micrograms.

Finally, check the label for how often to take supplements – daily or weekly. If you’ve ever been prescribed supplements by your doctor, they may have issued a regimen that includes high daily doses (the "loading" dose) for a couple of weeks, then weekly doses.

Pharmacists and other retailers are more likely to sell you daily supplements. If you’ve been taking too much, hold back for a few days. You could discuss this with your doctor or pharmacist if you have been on a high dose without guidance for a few weeks or more.

As mentioned, a note of caution if you are bottle-feeding your child. It’s likely the manufacturer has added enough vitamin D to meet their daily requirements. Formula-fed infants only need supplements if they are taking less than 500ml (a pint) of formula per day.

Signs of too much vitamin D

If you have worked out you’ve accidentally been taking too much, don’t panic. Vitamin D toxicity is rare and only usually occurs if you’ve taken a very large amount of vitamin D (more than 5000 IU daily) over a long period of time. Symptoms include feeling sick, vomiting and needing to urinate more. Long term risks occur from too much circulating calcium putting pressure on the kidneys and heart, or stress on the liver, where it is stored. If you are experiencing these symptoms or have concerns, it’s important to seek medical attention via an urgent visit with your doctor or NHS’s 111 service.

Depending on your symptoms and how much additional vitamin D you have taken, they may wish to examine you and send you for other investigations, such as blood tests. They can correct other abnormalities, but they may suggest avoiding vitamin D supplements until your body has worked through its existing stores.

Adults can safely take up to 4000 IU of vitamin D a day (100 micrograms), although it is best to speak with your pharmacist or doctor if you are planning to take more than the recommended maintenance dose. This maximum dose also applies to children aged 11 and over and women who are pregnant or breastfeeding. Children aged 1 to 10 years should have no more than 2000 IU (or 50 mcg), and those less than 1-year-old have a maximal dose of 100 IU (25 mcg) per day.

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Dr Roger Henderson
Reviewed by Roger Henderson
Reviewed on 29.04.2024
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