Investors in US corporate bonds had little reason to think they were in for difficult start to 2018. At the end of last year, there were few signs of incoming storm clouds for the US economy, as President Trump’s tax overhaul was poised to give a shot in the arm to corporate earnings.

But fund managers who make their living investing in the debt of America’s largest companies had underestimated the impact from two very different buyers of US bonds: Japanese insurance companies and the iPhone maker Apple.

Japanese institutional investors in search of higher yields have poured money into US investment-grade corporate bonds, because of the favourable arbitrage from swapping the dollar debt back into yen. At the same time, top-tier tech companies such as Apple, Alphabet and Microsoft became a big beast in the US bond market, as they invested their cash that was held overseas for tax reasons into the debt of other companies.