These are the worst things you can do for your immune system

The good news, according to South Yorkshire GP Dr Samar Mahmood, is that you can take steps to better protect yourself against bugs and infections this winter.

Here are the top five bad habits you might want to break to safeguard your seasonal health.

Smoking

Everyone knows that cigarettes damage your lungs, but smoking could be especially harmful during autumn and winter as your defences are weakened.

"Tobacco smoke irritates the airways and impairs the exchange of impure air for healthy air in and out of the lungs," explains Dr Mahmood. "This double whammy leaves you susceptible to respiratory infections including coughs, colds and chest infections."

Rather than waiting until the New Year to quit, it's a good idea to make it a winter resolution to stop smoking to stay fit and well. You're four times more likely to succeed in your quit attempt with expert support. You can book an appointment for smoking cessation support with your pharmacist through Patient Access.

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Poor diet

It can be all too easy to fill up on processed foods and snacks high in fat, salt and sugar, especially during Christmas and New Year festivities. Many of us also tend to drink more than we might normally.

Poor nutrition directly impairs the immune system, while being overweight or obese is also linked with low resistance to infection.

A balanced diet, conversely, keeps things ticking over. "Fresh fruit, vegetables and nuts - all easy to snack on - are rich in antioxidants and vitamins A, C and E, and these vital nutrients help maintain the integrity of the immune system," explains Dr Mahmood.

"Alcohol in large quantities - either binge drinking or frequent smaller amounts - compromises the cellular lining of the lungs, called the epithelium, making pathogens more likely to get in and cause infection," he adds.

Getting at least five portions of fruit and veg each day as part of a balanced diet and drinking plenty of water are vital to maintain your winter well-being.

Not getting enough sleep

Good-quality sleep helps to maintain your stores of bug-fighting components in your blood, which makes a decent night's rest particularly important when your defences are low. Late nights and early starts, therefore, are not conducive to keeping well in the winter months.

Dr Mahmood explains: "Among other important functions, sleep enables the release of more T cells and cytokines in the bloodstream, both of which are vital parts of our immune system. Less sleep therefore equals fewer immune cells, which means more chance of infection."

Sleep deprivation can also make it harder to manage stress, which triggers the release of cortisol. This hormone can itself weaken your immunity and leave you prone to picking up bugs.

It's crucial, then, to get enough quality sleep. Everybody needs different amounts of sleep to function optimally, but adults should aim for between seven and nine hours per day to stave off illness.

Not having the flu jab

Seasonal flu starts to take hold in autumn but is particularly virulent between December and March, and it can be serious.

"Influenza can kill," Dr Mahmood bluntly points out. "If you’ve been told you are eligible for the flu vaccination, it means that something about your health or your age group - or both – makes you more susceptible to the adverse effects of flu."

These factors include taking certain medication or having an illness that compromises your immunity to disease; having a long-term condition like asthma or diabetes; being pregnant; and being over 65.

However, fewer than half of people who are entitled to the free NHS vaccination take up the offer and, in turn, put themselves in danger of serious illness.

"The flu vaccine will not give you the flu - but it could just save your life!" Dr Mahmood adds. His advice is to make sure you're immunised every year to give yourself full protection.

You can check your eligibility and book your flu jab through Patient Access.

Poor hand hygiene

Following a healthy lifestyle can only do so much to prevent winter ailments. All your good work can be easily undone if you don't practise good hand hygiene.

Shockingly, four fifths of people globally don't wash their hands with soap and water after they've been to the toilet, leaving a hotbed of bacteria free to spread rapidly.

Everyone should wash their hands frequently (and properly) through the day, especially after using the toilet, changing a nappy or being in contact with animals, and before cooking, handling food, eating, and treating a cut or wound.

But it's also important to wash them after coughing, sneezing or blowing your nose - meaning reaching for the hand soap even more often during cold and flu season.

"Many infections can be spread through touch," says Dr Mahmood, "and this is particularly relevant in winter, wherein many of us are coughing or sneezing and might use our hands to cover our mouths."

It's recommended that you wash your hands using soap and water for around 20 seconds, and rinse and dry them thoroughly, to protect yourself and others.