Doctor issues warning over popular supplement that could trigger organ damage

Daily Mail​

09-05-2025

A GP has urged those who plan to take vitamin D to have a blood test to check their levels beforehand—as overdosing could result in heart and kidney damage.
Speaking in a video that has so far been watched over 52,000 times, Dr Asif Ahmed, revealed that he has seen far too many people taking a 'crazy' high dose of vitamin D, which can cause abnormal heart rhythms, kidney failure and bone pain.
It is currently estimated that around one in six adults in the UK do not get enough vitamin D—while some people, according to Dr Ahmed are overdosing on it.
Also known as the 'sunshine vitamin', the main source is exposure to sunlight, as well as from foods like oily fish, red meant and egg yolks.
NHS guidelines suggest taking a vitamin D supplement throughout the winter months, when there is less sunshine, but Dr Ahmed said taking too much of the vitamin could be dangerous.
'Taking vitamin D at high doses long term is actually very dangerous, because it can cause hypercalcemia', Dr Ahmed explained.
This is where excess calcium is deposited into the bloodstream, increasing the risk of heart and kidney disease.
Dr Ahmed explained that, unlikely other supplements that are difficult to overdose on, as excess comes out in your urine, vitamin D is fat soluble, which means it hangs around in the body.
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A post shared by Dr Asif Ahmed (MBBS, MRCGP, BSc) (@dra_says)
'A lot of the time when you take a high dose of vitamins, its not that dangerous because their water soluble and you just pee it out,' the GP explained.
'With fat soluble vitamins, like vitamin D however, we can't get rid of excess vitamins therefore it just accumulates in the body,' he added.
This can weaken the bones, and damage the kidneys and the heart.
'When it comes to dosage, I've seen people taking crazy high doses of something they've bought online, like 10,000 international units, which is a dose I wouldn't recommend for anyone,' the GP warned.
The NHS advises not to take more than 4,000 units of vitamin D a day. This applies to adults, including pregnant and breastfeeding women, the elderly, and children aged 11 to 17.
According to Dr Ahmed, most people only need around 10 micrograms, which is equivalent to 400 units.
While Dr Ahmed agreed with NHS guidelines that recommend a supplement dose of no more than 100 micrograms units a day, he said some people do need a much higher dose.
'These are patients who have very low vitamin D on their blood tests', he said.
In the US, the minimum threshold of vitamin D, set out by the institute of medicine, is 20ng/ml.
However, the UK's threshold for deficiency is much lower, at 12ng/ml, a level that has long been criticised by international health experts.
'The amount you need as a supplement depends on your symptoms, your ethnicity, your skin colour, but also your blood test result', Dr Ahmed cautioned.
This is why the doctor, who has over 95,500 followers on Instagram, urged anyone who takes vitamin D supplements to get a blood test to see if they are taking too much of the so-called sunshine vitamin.
He said: 'I urge most people taking vitamin D supplements to get their levels checked regularly.
You have to take it carefully and responsibly and not take too much of a high dose.'
Dr Ahmed is not the first medic to warn against megadoses of vitamin D.
NHS surgeon Doctor Karan Rajan previously suggested looking for vitamin D supplements that contain vitamin K2, which helps reduce the risk of calcium being deposited in the blood stream.
While supplements can help to boost vitamin D levels, experts say adequate sunlight exposure and a healthy diet that includes things like oily fish, red meat and fortified foods, are the best sources.