We're often told about ways to help strengthen our immune systems - but what about the things that might be doing it no favours at all?
Just as healthy lifestyle habits can play a key role in supporting our immune system, there may be certain things we're doing that possibly hinder it too - no matter how many oranges you've got piled up in your fruit bowl.
Here's seven things that could be negatively impacting your immune system...
1. Too many late nights
Sleep might not come as easily during anxious times like right now. In fact, the hashtag #cantsleep has recently been trending, as people share their frustrations with their off-kilter sleeping patterns.
Getting enough sleep not only feels great but it's also an essential function for the body, explains Dr Emer MacSweeney, medical director at Re:Cognition Health.
"As well as helping to maintain a healthy brain function, physical health, executive function and emotional wellbeing, it promotes a healthy immune system too," she says.
"It's all down to cytokines - a type of protein which is made and released during sleep. Cytokines target infection and inflammation in the body and create an immune response - so without sufficient sleep, our body produces fewer of these essential proteins, which can result in weaker immunity."
She recommends aiming for seven to nine hours of quality sleep each night and adds that naps are also a great way to top up, particularly if you're struggling with a bout of insomnia during lockdown.
The health risks of smoking have long been documented, and cigarettes can harm your immune system, as well as increasing your risk of developing respiratory illnesses and other major diseases, including many cancers and heart disease.
"The nicotine in cigarettes increases cortisol levels, reduces cell antibody formation and damages the lungs, which makes them more susceptible to infection," explains MacSweeney.
If you do smoke, why not try to use the lockdown as a prompt to cut down or quit entirely? Stopping smoking isn't easy but there's lots of support and online resources to help - and the rewards will be so worth it.
3. Not getting enough vitamin D
As well as strong bones and healthy blood cells, vitamin D is really important for keeping your immune system in good nick.
"We can only make vitamin D in our skin on exposure to sunlight when the UV index is greater than three," explains Dr Sarah Brewer, medical director at Healthspan.
"As a result, vitamin D deficiency is increasingly likely during autumn and winter in the UK, as there isn't enough sun for us to produce enough of it."
Even in springtime though, many people still fail to make enough vitamin D (and remember - it's always important to protect your skin from sun damage). Lockdown means many of us are spending more time indoors than usual too, so our vitamin D levels might be even lower.
"Vitamin D helps to activate macrophages - our hunter-killer immune cells that engulf and destroy viruses and bacteria, and stimulates the production of antibiotic-like proteins (defensins) within the lining of the respiratory tract," explains Brewer. "In fact, our immune cells, including B and T lymphocytes, all carry specific vitamin D receptors that help to regulate their activity."
As vitamin D deficiency is fairly widespread, Brewer recommends taking a daily supplement. Try Healthspan super strength vitamin D3 spray (£5.95 for 100 daily doses, healthspan.co.uk).
4. Not looking after your gut bacteria
As well as promoting digestion, 'friendly', lactic acid-producing bacteria in the lower part of the gut can help stimulate our resistance to infection - including viruses that may cause upper respiratory tract infections.
"Research involving 3,720 adults and children concluded that, compared with a placebo, taking a probiotic supplement can reduce the chance of experiencing at least one to three acute upper respiratory tract infections by 47%," says Brewer. "It also shortened the length of a cold, reduced antibiotic prescription rates and meant children took less time off school."
Gut-boosting supplements are not all created equally though. Plus, it's important to remember that your actual diet - the food you eat - is the most crucial factor, and a varied, balanced diet with plenty of fibre is essential for promoting healthy gut bacteria.
If you do want to consider a supplement too, Brewer advises: "When selecting a supplement, look for those that provide a known quantity of digestive bacteria, such as 10 billion to 50 billion colony forming units (CFU) per dose, and which provide at least three different strains for optimum benefit."
Try Vita Bright's bio cultures advanced multi strain complex (£15.99 for 60 capsules, vitabright.co.uk).
5. Not exercising enough
Regular movement is a key component of a healthy lifestyle. The NHS recommends everyone should do a minimum of 150 minutes a week of moderate-intensity aerobic exercise per week. Being fit and regularly physically active supports our health overall - including immune function.
"Exercise can help promote sleep and reduces the stress hormone cortisol, which can impair the functioning of cells that fight infection," notes MacSweeney.
"It also improves metabolic health, has anti-inflammatory influence on the body and helps delay the onset of ageing."
If you don't fancy the idea of gruelling bootcamp workouts, MacSweeney suggests dancing as an ideal way to keep active. Not only is it a heart-healthy cardio burn, but learning new routines is also an active workout for the brain.
6. Drinking too much
When you're feeling tired or anxious, it can be tempting to crack open a bottle of wine to soothe your worries, but MacSweeney warns that alcohol can weaken the immune system and make the body more susceptible to infections.
"Drinking in excess impairs (the) ciliary function of the lungs, which works to keep the airways clear of dirt and irritation," she says.
"It also reduces the immune system's response to bad bacteria, increasing the risk of infection," she adds - which is why heavy drinkers might notice they catch colds and other illnesses more.
If you do want to enjoy a drink, stick to the intake guidelines.
Studies have also found that people who are lonely or isolated may have less healthy immune function than those who feel more socially connected.
There might be a number of factors associated with exactly how loneliness and isolation impact our health.
However, MacSweeney also notes: "The increased anxiety associated with loneliness can be detrimental to the immune system. This is why it's important to keep socially active, even during lockdown."
If you live alone, stay in touch with friends, loved ones and colleagues through video chats, phone calls and messages.
"Virtual group gatherings through apps such as Zoom can also be arranged," she adds. "It's a great way to stay connected with friends and family throughout the challenging times we are currently living in."