We’ve been told for a long time about how people who wake up at silly o’clock in the morning achieve more than the rest of us – but perhaps it’s not about what time we wake up, so much as the amount of sleep we have.

Because, apparently, the more hours we sleep, the more money we are likely to earn.

A study by researchers in the US, has found that in locations where the days are shorter: ie where the sun sets earlier, people sleep for longer hours and also earn higher salaries.

So, although we might like to think that we are more perky and awake during the summer months, this might not be the case. Because later sunset time reduces worker sleep time and, resultantly, their wages.

The study found that sleeping for just one hour extra a week results in salary increases of 1.5% in the short term and by 4.9% long term (not to be sniffed at).

While workaholics may gasp at this information, arguing that if they’re awake for an hour longer then, surely, they can do an hour more of work than the sleepyheads – giving them a head start – study author, Jeffrey Shrader says that, in fact, the reason for this correlation is increased productivity resulting from getting a good night's sleep:

“The biggest effects come through employees who work on commission,” he tells The Guardian.

“If you go to work well rested, you are livelier and happier, and can sell more to increase your earnings.”

Interestingly, the areas in which people are likely to sleep longer – where it gets dark earlier – are also the areas with the most expensive house prices. So before we all start to relocate – it might be better just to invest in a sleep mask or some black-out blinds.

Struggling to sleep? Here are 10 proven ways to sleep like a baby.