Indeed, while you can get some vitamin D from your diet, many of the main sources of the vitamin – such as oily fish, eggs and fortified dairy products – are animal-based, meaning those on plant-based diets may be at greater risk of deficiency. The same is true for people from Black, Asian and mixed-race backgrounds, adds Toral Shah, a nutritional scientist and functional medicine practitioner. “Melanin makes it harder for you to make vitamin D,” she says. “The recommended levels are also set according to the needs of white people, so there aren’t enough studies to show much vitamin D people of colour need.”

The clocks going back at the end of last month could also be taking a toll on our ability to stay well. Not only is the hour’s shift enough to mess with our body clock, but the dark evenings and reduced daylight hours can also lead to circadian rhythm disruption, a condition where our body’s internal time is out of sync with the environment. “If your circadian rhythm is off, your body may not function at its best,” explains Theresa Schnorbach, Emma’s sleep scientist. “The quality of your sleep may also be reduced, meaning you wake in the night and have shallower sleep overall.”

These consequences of circadian rhythm disruption can affect our immunity in several ways – including when it comes to how well our immune system functions. You see, while our circadian rhythm is best known for impacting the sleep/wake cycle, it also plays a vital role in regulating our immune system. This is why disruptions to our body clock – whether driven by jet lag, shift work or the clocks changing – can put us at greater risk of falling ill.

Reductions in sleep quality and duration are also bad news for our immune system. “During sleep, your body secretes hormones involved in fighting disease,” explains Dr Sarah Brewer, a GP and author. “People who sleep for seven to eight hours have better immunity than those who are sleep deprived.” This link has been proven time and time again, with a famous study published in 2009 showing that those who chronically get less than seven hours of sleep a night are three times as likely to develop a common cold than those who routinely get more.

With this in mind, it’s hardly surprising that so many of us are feeling rubbish at the moment. Our bodies are dealing with a lot right now – and that’s not considering the added mental pressure many of us are feeling as seasonal affective disorder sets in. The reluctance to take sick days while working from home is also making it harder for us to recover; previous research found that remote working leads to an increase in ‘presenteeism’ – when people work more hours than required, for example, when they should be taking sick leave.

But here’s the thing – if we want to get better, now’s the time to prioritise rest, including taking sick days (and that means real sick days, not ‘I’ll just be working from home’ days) when they’re needed. If the pandemic taught us anything, it’s that the importance of protecting our health should never be underestimated. If staying in bed all day and watching Gilmore Girls is what your body needs right now, then that’s exactly what you should do. Doctor’s orders.

Need a tissue? The science behind why this is the snottiest week of the year