An unfounded belief Covid vaccines are leading to a rise in heart problems, especially in young athletes, has been amplified by Twitter owner Elon Musk.

Bronny James – son of basketball legend LeBron James – suffered a cardiac arrest on Monday while practising.

In a tweet about the incident, Mr Musk said that “we cannot ascribe everything to the Covid vaccine, but by the same token we cannot ascribe nothing”.

But there is no evidence to support the implication vaccines were involved.

Mr James’ family has thanked the doctors who helped him, and asked for privacy.

Twitter – which is in the process of rebranding itself as X – allows its users to produce “community notes”. These notes add further information to any Tweet considered misleading.

A community note contextualising Mr Musk’s comments initially appeared under his tweet, but it was removed overnight.

It’s not clear whether the note was removed by Twitter or because it was “downvoted” by other users.

Twitter has not yet responded to our request for comment.

In his tweet, Mr Musk also wrote that, “myocarditis is a known side effect,” in response to a post detailing Mr James’ hospital admission.

We have no information to suggest Mr James’s cardiac arrest was linked to myocarditis – inflammation of the heart muscle – or to the vaccine.

Pfizer and Moderna’s Covid vaccines have been linked to relatively rare cases of myocarditis, but crucially, studies suggest this does not lead to have a higher risk of having a cardiac arrest.

Myocarditis is more common and serious after Covid infections than after a vaccine.

However, there is evidence cardiac arrests are more common in athletes than in the general population.

Young athletes are more likely to experience a cardiac arrest than others their age.

There is also evidence that among US athletes, African American players are at the highest risk.

Mr Musk says, “We cannot ascribe everything to the Covid vaccine, but by the same token we cannot ascribe nothing”.

Yet it isn’t the case that nothing is being ascribed to Covid vaccines.

Health conditions, including myocarditis, have indeed been linked to some Covid vaccines – but only after careful medical examination.

A number of people have taken to Twitter to suggest seemingly speculating someone’s health condition has been caused by Covid vaccines without any evidence is unhelpful.

Mr Musk’s tweet has been taken as part of a wider trend of baselessly linking reports of illness and death to Covid vaccines before there are any facts available to support it.

BBC Verify has been investigating this trend and who has been spreading it.

Those caught in its crosshairs told the BBC of the additional distress that being trolled with conspiracy theories causes.

And experts have raised concerns that the spreading of unfounded links between illness and Covid vaccines sows distrust in public health information.

Glen Pyle, a professor who researches heart disease, said sudden cardiac incidents in athletes were not new, and had not increased following Covid vaccine rollouts.

He said speculating on this issue was, “irresponsible for anyone, but high profile people in particular”.

He added that linking Covid vaccines and cardiac arrest might “instil fear of a non-existent problem” that could discourage vaccination and therefore actually increase the risk of heart issues, which are “well-known to be linked to Covid”.

Additional reporting by Shayan Sardarizadeh.

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