The less well-off you are financially, the higher your risk of having heart problems, stats show. A new study provides compelling evidence for a key reason behind this phenomenon: poorer people just don't get as much sleep.
A tighter budget usually means people are more reliant on shift work, or have to hold down multiple jobs, or have no option but to work in noisy and demanding conditions – and none of those scenarios is helpful if you want to get a good night's sleep.
Then there's the extra stress and strain of living from payday to payday, which can easily lead to plenty of worried tossing and turning in bed at night. It seems that at least some of the association between economic status and heart health can be put down to how much quality shut-eye is involved.
This latest research pooled data on 111,205 individuals from eight previous studies across Europe, and found that 13.4 percent of the association between occupation and coronary heart disease could be attributed to a lack of sleep – though this factor only showed up significantly in men.
Study after study has linked sleep with all kinds of areas of wellbeing, such as our risk of depression and lapses in memory. Adequate rest is essential for restoring and recharging the body, and if we don't get enough sleep, we quickly start to feel it.
As for cardiovascular health, its association with sleep is now well established. At the height of the economic boom in 1980s Japan, for example, most of the deaths attributed to overworking were caused by heart problems.
The new study joins up some of these dots for the first time – the relationship between sleep, income, and cardiovascular disorders (CVD) isn't very well understood.
When it comes to the stronger demonstrated association between sleep, economic status, and CVD in men rather than women, the researchers suggest that women are generally more likely to already be under stress and strain from household responsibilities – so the burden of a manual, low-income job might be a smaller part of the picture for women than for men.
It's not difficult to think of other ways a wealthier lifestyle could lead to a more rested routine: it may mean you can afford a bigger house in a quieter neighbourhood, or might not have to travel so far to work, or could allow you to hire extra help around the house.
The study authors acknowledge the difficulty of pooling data across several different studies – which included a mix of self-reported and scientifically measured sleep, for example – so it's too early to say this link is definitively confirmed.
Still, it's an impressively large sample to have collated, and it certainly hints at how society could seek to lower the risk of heart disease in the poorest parts of our community: by finding ways to prioritise people having a good night's sleep.
"Structural reforms are needed at every level of society to enable people to get more sleep," says epidemiologist Dusan Petrovic from the University Centre of General Medicine and Public Health in Switzerland.
"For example, attempting to reduce noise, which is an important source of sleep disturbances, with double glazed windows, limiting traffic, and not building houses next to airports or highways."
The research has been published in Cardiovascular Research.