Your immune system is the first line of defence against infections and illness. When you're unwell, it produces antibodies designed to attack viruses, bacteria or toxins making you sick.
It's a complex system involving many different functions - and lots of things can affect how it's working and, in turn, how you feel. That's why it's always a good idea to look after your immune system, especially when the weather starts to get cold and wet.
Here experts explain some of the signs your immune system is run down, and what you can do about it…
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Tiredness
"When your immune system is busy fighting a low-grade infection, this often drains your energy reserves," said Susie Perry, food scientist and nutritionist from sisterlylab.com. "So, if you are feeling more fatigued than normal or feeling constantly under the weather, this is a sign that your immune system is busier than it would like to be."
Ms Perry added that if you suffer from recurrent cold sores, cystitis, an autoimmune condition, food allergies or intolerances, then your immune system could be working its socks off and may be running low on zinc and vitamins A, C and D3, leaving you vulnerable to common winter infections.
Digestion issues
Problems with digestion could also be a sign of a run down immune system. According to Dr Peter Abel, senior lecturer in biomedical sciences at the University of Central Lancashire, '70% of immune cells are in the gastrointestinal tract in the lining of the gut, and they normally fight toxins that may have been ingested'.
"They also regulate nutrients going in, so a weakened immune system can lead to stomach cramps and diarrhoea," he added.
Recurrent colds and flu
Often find you keep getting sick with cold and flu type symptoms? Dr Abel said: "A person with a run-down immune system may experience frequent colds.
"This is due to not making enough lymphocytes, which produce antibodies that fight viral infections. This can be caused by factors such as a poor diet.
"Vitamins such as B12, folic acid or zinc in the diet contribute to the production of these cells. If these vitamins are lacking, or over utilised, you may catch colds more frequently. It can also increase recovery time.
"Usually, you may expect two to three colds per year. More than four in a year is a possible sign of a weakened immune system."
Frequent infections
Infections are often obvious, with acute symptoms you can't fail to notice. Low-grade infections, however, can linger in the background, causing symptoms that aren't necessarily severe but still indicate something's not quite right.
"Low-grade infections aren't always obvious to spot, but bleeding gums might mean that you have a bacterial infection in your gums, athlete's foot is a skin fungus that your immune system may be struggling to get on top of, and having an upset tummy could actually be down to a gut or microbiome infection," said Ms Perry. "These infections constantly need your immune system’s attention and the immune cells in charge of clearing infections from the body are activated and supported by nutrients like zinc, vitamins C and D3.
"Over time, and if you don't have enough immune hero nutrients in your diet, these low-grade infections start winning and the immune system sends out another signal to alert you to the upscaled situation – chills, low-grade fever, runny nose and inflammation are your body's next level response. You may start noticing some pain and inflammation and other signs that your immune system is getting run down, like mouth ulcers or wounds that take longer to heal, because the immune system is busy elsewhere."
What can you do about it?
If you suspect your immune system is run-down or compromised, it's always a good idea to check in with your GP, so they can check for any possible underlying issues that need to be addressed. In addition to that, there are several simple diet and lifestyle steps London wellness coach Lauren Johnson Reynolds encourages, to help support normal immune function.
"Focus on a whole-food balanced diet rich in fruits, vegetables, protein, healthy fats and whole grains. Nutrients like vitamins C, D, and zinc play a crucial role in immune function,” Ms Reynolds said. "Engaging in regular physical activity can help improve immune function and reduce the risk of chronic diseases. Even 30 minutes three to four times per week is enough to have an impact.
"High levels of stress can weaken the immune system so practicing stress-reduction techniques like mindfulness, yoga or meditation can be beneficial."
Sleep is also essential for a healthy immune system. "So it's important to aim for seven to nine hours of sleep per night – if sleep is an issue, doing things to help regulate the circadian rhythm such as morning light exposure and wearing blue light blocking glasses at night make a huge difference," she added.
"Both smoking and excessive alcohol consumption can weaken the immune system. Quitting smoking and limiting alcohol intake are hugely beneficial."
Vitamins are also another great place to start when trying to build up your immune system. "Supplementing with vitamin D at this time of year is a must as we cannot absorb the sun between approximately October to April in the UK – it's a good idea to get levels tested and to supplement with a good quality, food based vitamin D," Ms Reynolds said.
"Remember that maintaining a healthy lifestyle is crucial for overall immune system function. If you experience persistent symptoms of immune system dysfunction, consult a healthcare professional for a proper diagnosis and treatment."
