I barely thought about sleep in my 20s; whether I got four or eight hours didn’t seem to make much difference to how I felt the next day. A couple of decades later and it’s a different story: a night spent tossing and turning leaves me headachey and prone to travel sickness and brain fog.

These hangover-style symptoms that worsen with age are our body’s way of telling us we’re missing out on something important. Research shows that sleep is no less fundamental to physical and mental wellbeing than diet and exercise. It is driven by two biological rhythms: sleep/wake homeostasis, which is determined by when we last slept, and circadian rhythm, the body’s internal 24-hour clock which is triggered by light and dark, and controlled by the part of our brain that regulates hormone levels that affect body temperature, appetite and sleepiness.

While scientists don’t yet fully understand the process of sleep, it is thought to be linked to regeneration and renewal of the body and brain. Studies have shown that, in the shorter term, not enough sleep is linked to higher infection risk, a poorer response to vaccination and worsened brain function. Remaining awake for 24 hours causes effects equivalent to being above the legal blood alcohol limit for driving in England, and road traffic accidents are linked to human circadian rhythms, peaking in the mid-afternoon and the early hours of the morning. In the longer term, poor sleep is associated with high blood pressure, cardiovascular disease, obesity and type 2 diabetes.

And now scientists have coined a term – “social jetlag” – to capture the effects of keeping irregular sleep patterns throughout the week. A new King’s College London study involving nearly 1,000 adults has found that one of the pathways by which erratic sleep habits might affect our health is via the gut. They found that even a 90-minute alteration in the midpoint of a night’s sleep during the course of a week correlated with lower levels of healthy bacteria in people’s digestive tracts, as a result of poorer dietary habits. Based on these findings, the researchers recommend people strive for consistent sleep patterns across the working week and weekend.

These insights about the importance of sleep have an intuitive ring, though there’s something wearying about adding yet another canon to entreaties to work out more, eat better and drink less. Sleep is very much a burgeoning part of the wellness industry and you could easily become as obsessed about sleep health as some people are about diet and exercise – think calculators that claim to work out when you should wake up based on the optimal point in your sleep cycle. As with so much public health advice, a rough rule of thumb feels like the healthiest approach; in light of evidence that many people are under-sleeping by an hour a night, the Royal Society for Public Health recommends adults aged 18-64 should be aiming for seven to nine hours a night.

But the wellness social gradient that runs through diet and fitness is particularly acute when it comes to sleep. It is true that exercising and eating healthily comes more easily the more cash you have; not just because they can be resource intensive, but because they take precious time. But if you’re a worker tied into shift work with very little choice over your night-time hours, it’s virtually impossible to achieve a healthy sleep pattern.

Some people may choose shift work because it suits them better. But many people work nights because they have little choice, it’s part and parcel of their job. Unsurprisingly, unsocial working hours outside the standard 9-5 are disproportionately shouldered by low-paid workers: the TUC estimates that seven in 10 night workers earn less than the median wage. Two of the biggest night-time sectors are health and social care, and the accommodation and food service industries.

Shift work comes with all the health disbenefits that the research on sleep would imply: people who work nights over the long term are at risk of poorer physical and mental health, and international health agencies have classed night work as “probably carcinogenic” after studies show elevated cancer risk for people working night shifts over several years. It can also be socially isolating; it is very difficult to maintain a family life or see friends when you’re spending days off trying to catch up on sleep. The Health and Safety Executive’s advice for people working shifts is a grim read that makes clear just how much we’re asking of people who work through the night.

Some of that work is vital: we will need growing numbers of people to do overnight care work as the population ages. But some is simply the flip side of what’s glibly termed the “night-time economy”. The convenience of food delivered any time and drinking until the small hours comes at a health and social cost to those who do that work, for which there is absolutely no pay premium.

This lack of control over your time is a feature of low-paid, insecure work more broadly. Financial compensation is not the only indication of where power lies in the workplace; so are working conditions, including workers’ ability to shape how they fit their work round their life. A lack of understanding of that power dynamic leads people to see the same type of work very differently. The government minister, Mel Stride, regards a firm such as Deliveroo as a flexible nirvana for over-50s out of work. Speak to workers in the gig economy and the story is one of hours dictated by the big platforms responding to consumer demand and struggles over what constitutes paid time.

I’m a big fan of the four-day week and the idea that we should all work fewer hours. But you can see why that would feel ridiculously aspirational to someone locked into an exhausting schedule of working five night shifts, week in, week out, for little pay, in a way they can feel is bad for their health. It is a sobering reminder that workplace inequality is about more than how much someone is paid, and that we aren’t always prepared to pay the true cost of the convenience we demand.

• Sonia Sodha is an Observer columnist