Stock markets set a curious record last year — Apple gained more in equity value than any other company in history. But rather than gawp at the rise, equity investors need to consider whether the size of the company, and that of its brethren among the top five in the US — Microsoft, Amazon, Facebook and Google’s parent Alphabet — presents a growing risk to portfolios.

Apple’s stock surged 86 per cent in 2019, sending the iPhone maker’s market capitalisation to $1.3tn — a gain of $556bn. That in itself is bigger than all but the top four S&P 500 companies and is roughly equal to adding the entire Spanish or Italian stock market.

The gains owe much to the peculiarities of the calendar. Shares in Apple faded toward the end of 2018 when it revealed weak sales forecasts in China and then slid further during a general December sell-off that year. So the rise came from a low base. Yet keep in mind that 2019 was no banner year for Apple product launches and the market was not wild about the streaming service unveiled in March.