Naomi O’leary and

Yet these data come with their own health warning – most of them are collected from media reports of high-profile sporting deaths.

There are no proper registries to collect numbers, either within a specific sport or country, or cross-border and cross-discipline.

For the best clues, experts point to one of the largest studies on SCD conducted in the United States between 2004 and 2008 in the National Collegiate Athletic Association (NCAA).

It found SCD is over three times more common in African-americans than Caucasians. This varied greatly across sports.

In American Football, SCD rates are four times higher in Caucasians than AfricanAmericans. In soccer there were no cardiac events recorded during the five-year period.

Having searched this and other scientific literature on sudden deaths in sport, experts writing in the BJSM – including sports scientists from the English Football Association, the London-based Royal Ballet and world soccer governing body Fifa’s Medical Assessment and Research Centre in Switzerland – say there are far too many questions unanswered.

“There’s so much we don’t know,” Weiler said in a telephone interview. “We don’t know what triggers sudden cardiac death. We don’t understand the risks in different sports, we don’t understand whether race and genetics have an impact, and we don’t know why many cases of sudden cardiac death remain unexplained.”

Though these deaths are sudden and unexpected, Sharma, who is also a consultant cardiologist at St George’s Hospital in London, says most heart specialists have tools to diagnose the conditions that cause them, pinpointing those most at risk.

They are usually caused by hereditary electrical or structural faults of the heart that show up in heart scans or in family history, he says.

This leads some sports scientists to say more widespread screening may be the answer.

Fifa recommends cardiac screening and sets it as a requirement for players in teams taking part in its tournaments, but there are no set rules across sports or borders.

Sharma cites data from the Veneto region of Italy, which suggest a programme that screens athletes every year and bans people with worrying conditions from taking part in competitive sport has cut the number of sudden cardiac deaths in athletes by 90% – from 3.6 per 100 000 person-years in 1979-1980 to 0.4 per 100 000 person-years in 2003-2004.

But the Italian programme disqualified 2% of all athletes, leading critics to say that for every one death prevented, around 1 000 athletes are needlessly banned from competing in a sport they love.

“We don’t really understand what we’re looking for yet,” said Weiler. — Reuters